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Sökning: WFRF:(Bäck Sven)

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1.
  • Adrian, Gabriel, et al. (författare)
  • The FLASH effect depends on oxygen concentration
  • 2019
  • Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 1748-880X .- 0007-1285. ; 93:1106
  • Tidskriftsartikel (refereegranskat)abstract
    • OBJECTIVE: Recent in vivo results have shown prominent tissue sparing effect of radiotherapy with ultra-high dose rates (FLASH) compared to conventional dose rates (CONV). Oxygen depletion has been proposed as the underlying mechanism, but in vitro data to support this have been lacking. The aim of the current study was to compare FLASH to CONV irradiation under different oxygen concentrations in vitro. METHODS: Prostate cancer cells were irradiated at different oxygen concentrations (relative partial pressure ranging between 1.6 and 20%) with a 10 MeV electron beam at a dose rate of either 600 Gy/s (FLASH) or 14 Gy/min (CONV), using a modified clinical linear accelerator. We evaluated the surviving fraction of cells using clonogenic assays after irradiation with doses ranging from 0 to 25 Gy. RESULTS: Under normoxic conditions, no differences between FLASH and CONV irradiation were found. For hypoxic cells (1.6%), the radiation response was similar up to a dose of about 5-10 Gy, above which increased survival was shown for FLASH compared to CONV irradiation. The increased survival was shown to be significant at 18 Gy, and the effect was shown to depend on oxygen concentration. CONCLUSION: The in vitro FLASH effect depends on oxygen concentration. Further studies to characterize and optimize the use of FLASH in order to widen the therapeutic window are indicated. ADVANCES IN KNOWLEDGE: This paper shows in vitro evidence for the role of oxygen concentration underlying the difference between FLASH and CONV irradiation.
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2.
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3.
  • Aznar, MC, et al. (författare)
  • Real-time optical-fibre luminescence dosimetry for radiotherapy: physical characteristics and applications in photon beams
  • 2004
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 49:9, s. 1655-1669
  • Tidskriftsartikel (refereegranskat)abstract
    • A new optical-fibre radiation dosimeter system, based on radioluminescence and optically stimulated luminescence from carbon-doped aluminium oxide, was developed and tested in clinical photon beams. This prototype offers several features, such as a small detector (1 x 1 x 2 mm), high sensitivity, real-time read-out and the ability to measure both dose rate and absorbed dose. The measurements describing reproducibility and output dependence on dose rate, field size and energy all had standard deviations smaller than 1%. The signal variation with the angle of incidence was smaller than 2% (1 SD). Measurements performed in clinical situations suggest the potential of using this real-time system for in vivo dosimetry in radiotherapy.
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4.
  • Baldoc, C, et al. (författare)
  • Dose resolution in radiotherapy polymer gel dosimetry: effect of echo spacing in MRI pulse sequence
  • 2001
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 46:2, s. 449-460
  • Tidskriftsartikel (refereegranskat)abstract
    • In polymer gel dosimetry using magnetic resonance imaging, the uncertainty in absorbed dose is dependent on the experimental determination of T2. The concept of dose resolution (Dpdelta) of polymer gel dosimeters is developed and applied to the uncertainty in dose related to the uncertainty in T2 from a range of T4 encountered in polymer gel dosimetry. Dpdelta is defined as the minimal separation between two absorbed doses such that they may be distinguished with a given level of confidence, p. The minimum detectable dose (MDD) is Dpdelta as the dose approaches zero. Dpdelta and the minimum detectable dose both give a quantifiable indication of the likely practical limitations and usefulness of the dosimeter. Dpdelta of a polyacrylamide polymer gel dosimeter is presented for customized 32-echo and standard multiple-spin-echo sequences on a clinical MRI scanner. In evaluating uncertainties in T2, a parameter of particular significance in the pulse sequence is the echo spacing (ES). For optimal results, ES should be selected to minimize Dpdelta over a range of doses of interest in polymer gel dosimetry.
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5.
  • Bjoreland, Anders, et al. (författare)
  • Liquid ionization chamber calibrated gel dosimetry in conformal stereotactic radiotherapy of brain lesions
  • 2008
  • Ingår i: Acta Oncologica. - : Informa UK Limited. - 1651-226X .- 0284-186X. ; 47:6, s. 1099-1109
  • Tidskriftsartikel (refereegranskat)abstract
    • Hypofractionated conformal stereotactic radiotherapy (HCSRT) is an established method of treating brain lesions such as arteriovenous malformations (AVMs) and brain metastases. The aim of this study was to investigate the reliability of treatment plans in the terms of dose distribution and absorbed dose for HCSRT. Methods and materials. Treatment plans for three different clinical intracerebral targets, AVMs, were transferred to a CT study of a spherical water filled phantom simulating the human head and recalculated for the phantom geometry using a standard treatment planning system utilizing a pencil beam algorithm for dose calculation. The calculated absorbed dose, relative three dimensional (3D) dose distribution and dose conformity were investigated using gel dosimetry normalized to liquid ionization chamber (LIC) measurements. Results. The measured absorbed dose to the dose reference point was found to be within 2% of the calculated dose for all three targets. The measured dose distribution was found to be within 3% and 2 mm of the calculated dose for more than 93% of all points in the target volume for all three targets. Conclusions. The results show that the investigated standard treatment planning system can correctly predict the absorbed dose and dose distribution in different types of intracerebral targets and that the treatment can be delivered according to the plan.
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6.
  • Bäck-Pettersson, Siv, 1946, et al. (författare)
  • FOU-kompetensförsörjningsprogram för sjuksköterskor i Fyrbodal
  • 2012
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Sammanfattning Betydelsen av FoU-kompetensförsörjningsprogrammet som varit en medveten och strategisk satsning inom FoU-området kan sammanfattas på följande sätt: Deltagarnas behållning och föreskriven akademisk utveckling har haft en närmast hundraprocentig måluppfyllelse och gett kliniskt verksamma sjuksköterskor en bra start på sin akademiska karriär. Programmet illustrerar ett effektivt sätt att stimulera sjuksköterskors livslånga lärande genom att bygga upp förmågan att genomföra och tillämpa omvårdnadsforskning i klinisk praktik. Programmet har också bidragit till utvecklingen av kompetenta handledare för studenter under utbildning. Flertalet av deltagarna har utvecklat både en önskan om och kompetens för att ta på sig ledande uppdrag såväl inom den egna verksamheten som i gränsöverskridande projekt både inom Fyrbodal och nationellt. Programmet har medverkat till att bryta revirtänkande och kan bidra till en mer öppen och gränsöverskridande kultur inom Fyrbodalområdets hälso- och sjukvård. Det har även medverkat till att deltagarna skaffat sig en helhetssyn på och förståelse för olika vårdverksamheter. Programmets design kan användas för att utveckla såväl professionell som vetenskaplig kompetens och kan med fördel användas inom andra yrkesgrupper med medellång vårdutbildning, eller för en tvärprofessionell grupp.
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7.
  • Bäck-Pettersson, Siv, 1946, et al. (författare)
  • Nurses´Experiences of participation in a research and development programme
  • 2013
  • Ingår i: Journal of Clinical Nursing. - : Wiley. - 0962-1067 .- 1365-2702. ; 22:7-8, s. 1103-1111
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims and objectives. To describe clinical nurses’ experience of participating in a Research and Development (R&D) programme and its influence on their research interest and ability to conduct and apply nursing research. Background. To stimulate nurses’ research interest and to overcome barriers for building research capacity in nursing, there is a need for sustainable research programmes. A two-year programme was designed for nurses, to take part in both an academic education for master and research seminars and workshops to conduct a research project from idea to publication. Design. A qualitative approach using using focus group interviews. Methods. Registered nurses (n = 12) with a bachelor’s degree in nursing, participated. Data were collected in focus group interviews, after one year and when the programme ended. Content analysis was used to analyse the data. Results. The findings consist of two themes: being a traveller in the world of nursing research, which included three categories, and experiencing professional growth as a result of nursing research training, in both cases focusing on the experience of students involved in a cohesive programme which included four categories: discovering new dimensions of clinical nursing practice; selected and confirmed; supported by professional others; development of professional self-concept. Conclusions. To support early career researchers, there is a need for strong leadership, an organisational and supportive infrastructure underpinning research capability building in nurses. In this context, research strategies, programmes and collaboration between leaders of academia and clinical institutions appear to be essential. Relevance to clinical practice. The R&D programme illustrates an effective way of stimulating nurses’ lifelong learning by building the capacity to conduct and apply nursing research in clinical practice. The structure of the programme can be used as a model in other contexts.
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8.
  • Bäck, Sven, et al. (författare)
  • Ferrous sulphate gel dosimetry and MRI for proton beam dose measurements
  • 1999
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 44:8, s. 1983-1996
  • Tidskriftsartikel (refereegranskat)abstract
    • Ferrous sulphate gel dosimetry has the potential for measurement of absorbed dose distributions in proton therapy. The chemical properties of the gel are altered according to the radiation dose and these changes can be evaluated in three dimensions using MRI. The purpose of this work was to investigate the properties of a ferrous gel used with clinical proton beams. The gel was irradiated with both monoenergetic and range-modulated proton beams. It was then evaluated using MRI. The depth dose by means of the 1/T1 distribution was studied and compared with data from a plane-parallel plate ionization chamber. 1/T1 was shown to be proportional to the dose at a mean proton energy of approximately 90 MeV. The dose response was no different from that obtained using photon beams. However, on normalization at the entrance, the relative 1/T1 at the Bragg peak was 15-20% lower than the corresponding ionization chamber data for the monoenergetic proton beam. Better agreement was found for the modulated beam, but with significant differences close to the distal edge of the 1/T1 distribution. The change in sensitivity with depth was explained by means of a linear energy transfer dependence. This property was further studied using Monte Carlo methods.
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9.
  • Bäck, Sven (författare)
  • Implementation of MRI gel dosimetry in radiation therapy
  • 1998
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Gel dosimetry was used together with magnetic resonance imaging (MRI) to measure three-dimensional absorbed dose distributions in radiation therapy. Two different dosimeters were studied: ferrous- and monomer gel, based on the principles of radiation-induced oxidation and polymerisation, respectively. Single clinical electron and photon beams were evaluated and gel dose distributions were mainly within 2% of conventional detector results. The ferrous-gel was also used for clinical proton beams. A decrease in signal per absorbed dose was found close to the end of the range of the protons (15-20%). This effect was explained as a linear energy transfer dependence, further supported with Monte Carlo simulations. A method for analysing and comparing data from treatment planning system (TPS) and gel measurements was developed. The method enables a new pixel by pixel evaluation, isodose comparison and dose volume histogram verification. Two standard clinical radiation therapy procedures were examined using the developed TPS verification method. The treatment regimes included several beams of different radiation qualities. The TPS calculated data were in very good agreement with the dose distribution measured by the ferrous-gel. However, in a beam abutment region, larger dose difference was found. Beam adjustment errors and a minor TPS underestimation of the lateral scatter contribution outside the primary electron beam may explain the discrepancy. The overall uncertainty in the ferrous-gel dose determination was considerably reduced using an optimised MRI acquisition protocol and a new MRI scanner. The relative dose uncertainty was found to be better than 3.3% for all dose levels (95% confidence level). Using the method developed for comparing measured gel data with calculated treatment plans, the gel dosimetry method was proven to be a useful tool for radiation treatment planning verification.
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10.
  • Bäck, Sven, et al. (författare)
  • Improvements in absorbed dose measurements for external radiation therapy using ferrous dosimeter gel and MR imaging (FeMRI)
  • 1998
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 43, s. 261-
  • Tidskriftsartikel (refereegranskat)abstract
    • A ferrous gel, based on ferrous (Fe) sulphate and agarose, was used with a clinical magnetic resonance imaging (MRI) scanner to obtain relative dose distribution data from therapeutic photon and electron beams. The FeMRI gel was scanned using a new MRI acquisition protocol optimized for T1 measurements. Thorough comparisons with silicon semiconductor detector and ionization chamber measurements, as well as with Monte Carlo calculations, were performed in order to quantify the improvements obtained using FeMRI for dose estimations. Most of the relative doses measured with FeMRI were within 2% of the doses measured with other methods. The larger discrepancies (2-4%) found at shallow depths are discussed. The uncertainty in relative dose measurements using FeMRI was significantly improved compared with previously reported results (5-10%, one standard deviation, 1 SD), and is today between 1.6% and 3.3% (depending on dose level, 2 SD). This corresponds to an improvement in the minimum detectable dose (3 SD above background) from approximately 2 Gy to better than 0.6 Gy. The results obtained in this study emphasize the importance of obtaining basic FeMRI dose data before the method is extended to complicated treatment regimes.
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11.
  • Bäck, Sven, et al. (författare)
  • Investigation of the NMR relaxation rate dose-response of a ceric sulphate dosimeter
  • 2002
  • Ingår i: Applied Radiation and Isotopes. - 0969-8043. ; 56:6, s. 895-899
  • Tidskriftsartikel (refereegranskat)abstract
    • The relationship between the radiation absorbed dose and the NMR longitudinal and transversal relaxation rates, R-1 and R-2, respectively, of a ceric sulphate dosimeter was examined. By adding copper sulphate, the R-1 and R-2 dose-responses were found to be linear up to 60 kGy with dose sensitivities of 13 x 10(-6) and 15 x 10(-6) s(-1) Gy-1, respectively. There is thus the potential for a three-dimensional ceric dosimeter for high dose applications. provided a suitable gelling substance is used.
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12.
  • Børresen, Betina, et al. (författare)
  • Evaluation of single-fraction high dose FLASH radiotherapy in a cohort of canine oral cancer patients
  • 2023
  • Ingår i: Frontiers in Oncology. - 2234-943X. ; 13, s. 1-10
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: FLASH radiotherapy (RT) is a novel method for delivering ionizingradiation, which has been shown in preclinical studies to have a normal tissuesparing effect and to maintain anticancer efficacy as compared to conventionalRT. Treatment of head and neck tumors with conventional RT is commonlyassociated with severe toxicity, hence the normal tissue sparing effect of FLASHRT potentially makes it especially advantageous for treating oral tumors. In thiswork, the objective was to study the adverse effects of dogs with spontaneousoral tumors treated with FLASH RT.Methods: Privately-owned dogs with macroscopic malignant tumors of the oralcavity were treated with a single fraction of ≥30Gy electron FLASH RT andsubsequently followed for 12 months. A modified conventional linear acceleratorwas used to deliver the FLASH RT.Results: Eleven dogs were enrolled in this prospective study. High grade adverseeffects were common, especially if bone was included in the treatment field. Fourout of six dogs, who had bone in their treatment field and lived at least 5 monthsafter RT, developed osteoradionecrosis at 3-12 months post treatment. Thetreatment was overall effective with 8/11 complete clinical responses and 3/11partial responses.Conclusion: This study shows that single-fraction high dose FLASH RT wasgenerally effective in this mixed group of malignant oral tumors, but the risk ofosteoradionecrosis is a serious clinical concern. It is possible that the risk ofosteonecrosis can be mitigated through fractionation and improved doseconformity, which needs to be addressed before moving forward with clinicaltrials in human cancer patients.
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13.
  • Ceberg, Sofie, et al. (författare)
  • Dosimetric verification of breathing adapted radiotherapy using polymer gel
  • 2006
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 56:1, s. 300-303
  • Konferensbidrag (refereegranskat)abstract
    • In radiation therapy patient movement caused by respiration can be a major challenge to the ambition to deliver a high absorbed dose to the target volume while minimizing the dose to normal tissues. Large respiratory motion requires increased margins, which implies an increased risk of morbidity from late toxicity. It is therefore important to take respiratory motion into account when treating targets in the thorax region. The aim of this study was to investigate the feasibility of using a 3D gel dosimeter for dose verification of breathing adapted radiotherapy
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14.
  • Ceberg, Sofie, et al. (författare)
  • Evaluation of breathing interplay effects during VMAT by using 3D gel measurements
  • 2013
  • Ingår i: 7th International Conference on 3D Radiation Dosimetry (IC3DDose). - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 444, s. 012098-012098
  • Konferensbidrag (refereegranskat)abstract
    • Respiratory motion during dynamic radiotherapy may affect the absorbed dose distribution both by dose-reducing smoothing and by more complicated interplay effects. In this study we present a novel method to determine the relative importance of these two effects. For the two dynamic deliveries studied in this work, the expected target dose reduction due to the smoothing effect was estimated by measurements convolved by the motion function. Remaining absorbed dose differences were attributed to interplay effects between the motion of the gel phantom and the movement of the modulating MLC leaves during modulated arc radiotherapy. The total dosimetric effect due to breathing motion and dynamic MLC motion during VMAT delivery resulted in an average of about 4% target dose reduction. Comparing with only the smoothing effect, the average difference was decreased to around 1%, and the remaining distribution was attributed to interplay effects. Although the interplay effects were small compared to the smoothing effect, the standard deviations of 1.4-2.3% (1SD) were larger than the narrow distribution for repeated stationary measurement with a standard deviation between 0.5-0.9% (1SD).
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15.
  • Ceberg, Sofie, et al. (författare)
  • Modelling the dynamic dose response of an nMAG polymer gel dosimeter.
  • 2012
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 57:15, s. 4845-4853
  • Tidskriftsartikel (refereegranskat)abstract
    • Gel dosimetry measures the absorbed radiation dose with high spatial resolution in 3D. However, recently published data show that the response of metacrylic-based polymer gels depends on the segmented delivery pattern, which could potentially be a considerable disadvantage for measurements of modern dynamic radiotherapy techniques. The aim of this study is to design a dynamic compartment model for the response of a gel dosimeter, exposed to an arbitrary irradiation pattern (segmented delivery and intensity modulation), in order to evaluate the associated effects on absorbed dose measurements. The model is based on the separation of the protons affecting the magnetic resonance signal (i.e. the R2 value) into six compartments, described by a set of differential equations. The model is used to calculate R2 values for a number of different segmented delivery patterns between 0-4 Gy over 1-33 fractions. Very good agreement is found between calculated and measured R2 values, with an average difference of 0.3 ± 1.1% (1 SD). The model is also used to predict the behaviour of a gel dosimeter exposed to irradiation according to typical IMRT, VMAT and respiratory gating scenarios. The calculated R2 values are approximately independent of the segmented delivery, given that the same total dose is delivered during the same total time. It is concluded that this study helps to improve the theoretical understanding of the dependence of metacrylic-based polymer gel response to segmented radiation delivery.
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16.
  • Ceberg, Sofie, et al. (författare)
  • Radiotherapy delivery during motion
  • 2010
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 250
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper discusses the 3D dosimetric consequences of radiotherapy delivery during two kinds of motion, (i) the respiratory motion by the patient and (ii) the motion by the gantry while rotating around the patient. Respiratory motion primarily compromises treatments in the thorax and abdomen regions. Several strategies to reduce respiratory motion effects have been developed or are under development. The organ motion could for instance be measured and incorporated in the treatment planning, or adapted to by using respiratory gating and tumour-tracking delivery techniques. Gantry motion is involved in various forms of intensity-modulated arc-therapy techniques. The purpose is to increase the modulation by simultaneously varying the MLC positions, the rotation speed of the gantry, and the dose rate during the treatment. The advantage of these techniques is the increased possibility to deliver a high absorbed dose to the target volume while minimizing the dose to normal tissues. However, the dosimetric uncertainties associated with motion, small fields and steep dose gradients, has to be evaluated in detail, and this requires adequate true 3D dose-verification tools.
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17.
  • Ceberg, Sofie, et al. (författare)
  • RapidArc treatment verification in 3D using polymer gel dosimetry and Monte Carlo simulation.
  • 2010
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 55:17, s. 4885-4898
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study was to verify the advanced inhomogeneous dose distribution produced by a volumetric arc therapy technique (RapidArc) using 3D gel measurements and Monte Carlo (MC) simulations. The TPS (treatment planning system)-calculated dose distribution was compared with gel measurements and MC simulations, thus investigating any discrepancy between the planned dose delivery and the actual delivery. Additionally, the reproducibility of the delivery was investigated using repeated gel measurements. A prostate treatment plan was delivered to a 1.3 liter nPAG gel phantom using one single arc rotation and a target dose of 3.3 Gy. Magnetic resonance imaging of the gel was carried out using a 1.5 T scanner. The MC dose distributions were calculated using the VIMC-Arc code. The relative absorbed dose differences were calculated voxel-by-voxel, within the volume enclosed by the 90% isodose surface (VOI(90)), for the TPS versus gel and TPS versus MC. The differences between the verification methods, MC versus gel, and between two repeated gel measurements were investigated in the same way. For all volume comparisons, the mean value was within 1% and the standard deviation of the differences was within 2.5% (1SD). A 3D gamma analysis between the dose matrices were carried out using gamma criteria 3%/3 mm and 5%/5 mm (% dose difference and mm distance to agreement) within the volume enclosed by the 50% isodose surface (VOI(50)) and the 90% isodose surface (VOI(90)), respectively. All comparisons resulted in very high pass rates. More than 95% of the TPS points were within 3%/3 mm of both the gel measurement and MC simulation, both inside VOI(50) and VOI(90). Additionally, the repeated gel measurements showed excellent consistency, indicating reproducible delivery. Using MC simulations and gel measurements, this verification study successfully demonstrated that the RapidArc plan was both accurately calculated and delivered as planned.
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18.
  • Ceberg, Sofie, et al. (författare)
  • RapidArc™ treatment verification using polymer gel dosimetry
  • 2009
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 164:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study was to verify a novel volumetric arc therapy technique, RapidArc". Polymer gel dosimetry system was used to measure the advanced inhomogeneous 3D dose distribution produced using the technique RapidArc". A preclinical installation of the novel beam delivery approach was set up on a linear accelerator at Rigshospitalet in Copenhagen. A prostate treatment plan was delivered to a 1.3 l nPAG gel phantom using one single arc rotation from 200 to 160 degrees, and a target dose of 3.3 Gy. Magnetic resonance imaging of the gel was carried out using the 1.5 T scanner and MATLAB was used for image processing and 3D rendering. The difference in relative absorbed dose between the treatment planning system (TPS) and gel measurement was calculated voxel by voxel within the 80% and the 95% isodose volume, respectively. Measurements agreed well with the TPS within the treated volume. Within both isodose volumes 90% of the voxels showed a deviation less or equal to 5%. This study shows that the 3D gel dosimetry system is a useful tool for dose verification of advanced treatment delivery techniques.
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19.
  • Ceberg, Sofie, et al. (författare)
  • Tumor-tracking radiotherapy of moving targets; verification using 3D polymer gel, 2D ion-chamber array and biplanar diode array
  • 2010
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 250:1, s. 235-239
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study was to carry out a dosimetric verification of a dynamic multileaf collimator (DMLC)-based tumor-tracking delivery during respiratory-like motion. The advantage of tumor-tracking radiation delivery is the ability to allow a tighter margin around the target by continuously following and adapting the dose delivery to its motion. However, there are geometric and dosimetric uncertainties associated with beam delivery system constraints and output variations, and several investigations have to be accomplished before a clinical integration of this tracking technique. Two types of delivery were investigated in this study I) a single beam perpendicular to a target with a one dimensional motion parallel to the MLC moving direction, and II) an intensity modulated arc delivery (RapidArc®) with a target motion diagonal to the MLC moving direction. The feasibility study (I) was made using an 2D ionisation chamber array and a true 3D polymer gel. The arc delivery (II) was verified using polymer gel and a biplanar diode array. Good agreement in absorbed dose was found between delivery to a static target and to a moving target with DMLC tracking using all three detector systems. However, due to the limited spatial resolution of the 2D array a detailed comparison was not possible. The RapidArc® plan delivery was successfully verified using the biplanar diode array and true 3D polymer gel, and both detector systems could verify that the DMLC-based tumor-tracking delivery system has a very good ability to account for respiratory target motion.
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20.
  • Ceberg, Sofie, et al. (författare)
  • Verification of dynamic radiotherapy: the potential for 3D dosimetry under respiratory-like motion using polymer gel.
  • 2008
  • Ingår i: Physics in Medicine and Biology. - 1361-6560. ; 53:20, s. 387-396
  • Tidskriftsartikel (refereegranskat)abstract
    • Following the implementation of advanced treatment procedures in radiotherapy, there is a need for dynamic dose verification in 3D. Gel dosimetry could potentially be used for such measurements. However, recently published data show that certain types of gels have a dose rate and fractionation dependence. The aim of this study was to investigate the feasibility of using a polymer gel dosimeter for dose verification of dynamic radiotherapy. To investigate the influence of dose rate dependence during respiratory-like motion in and out of the beam, a respiration robot together with two types of gel systems (normoxic methacrylic acid gel (nMAG) and normoxic polyacrylamide gel (nPAG)) were used. Reference measurements were obtained using a linear diode array (LDA). Expected results, if there was no influence of the dose rate variation, were calculated by convolving the static irradiated gel data with the motion function controlling the robot. To investigate the fractionation dependence, the gels were irradiated using gated and ungated deliveries. Magnetic resonance imaging was used to evaluate the absorbed dose response of the gel. The measured gel data coincided well with the LDA data. Also, the calculated data agreed well with the measured dynamic gel data, i.e. no dose rate dependence due to motion was observed. The difference in the R2 response for the gels receiving ungated and gated, i.e. fractionated, deliveries was less than 1% for the nPAG and 4% for the nMAG, for absorbed doses up to 2 Gy. The maximum difference was 1.2% for the nPAG and 9% for the nMAG, which occurred at the highest given dose (4 Gy). The investigated gels were found to be feasible detectors for dose measurements under respiratory-like motion. For dose verification of dynamic RT involving gated delivery, e.g. breathing-adapted radiotherapy, relative absorbed dose evaluation should be used in order to minimize the effects of fractionated irradiation.
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21.
  • Fransson, Kristin, et al. (författare)
  • Miljöhandbokför upphandlare
  • 2015
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Hållbar utveckling innefattar såväl social, ekonomisk som miljömässig hållbar utveckling.I Miljöhandboken kommer dessa tre aspekter av hållbar utveckling att behandlas,dock ligger störst fokus på miljöaspekterna.Miljöhandboken ska hjälpa upphandlare att ställa relevanta miljökrav vid upphandlingoch är ett komplement till exempelvis Konkurrensverkets (f.d. Miljöstyrningsrådets)upphandlingskriterier och ska bidra med fakta kring hur miljökrav kan ställas.Miljökrav vid upphandling kan innefatta bl. a. energianvändning, livslängd, skadligaämnen, strålning, återvinning och miljöledningssystem. Kravens betydelse påverkasbl. a. av upphandlingens omfattning och miljömognaden inom produktsegmentet. Imiljöhandboken presenteras inga specifika kriterier eller gränsvärden för olika miljöaspekter,i stället ges länkar till exempelvis lagstiftning, myndigheter och miljömärkningar.Detta för att kriterier och gränsvärden uppdateras kontinuerligt som en följdav teknikutveckling men också för att den samlade kunskapen om vad som är miljöproblemständigt växer och kan ge upphov till nya kriterier och gränsvärden. Tyngdpunkteni denna handbok ligger på miljöpåverkan ur ett livscykelperspektiv, vilket innebäratt hänsyn tas till miljöpåverkan från utvinning av råmaterial till resthantering aven produkt.
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22.
  • Guldbrandsson, Karin, et al. (författare)
  • The significance of policy documents in municipal child health promotion
  • 2008
  • Ingår i: Scandinavian Journal of Public Health. - : SAGE Publications. - 1403-4948 .- 1651-1905. ; 36:3, s. 228-234
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims: To investigate municipal utilization of policy documents in child health-promoting activities with reference to document types, substance in the documents and timing in the policy process. Methods: Fifty semi-structured interviews were performed using the snowball method, and content analyses of written documentation were made. Data were categorized by means of a policy process matrix, and nine case studies were written. Triangulation was used as a validating method, and the coding reliability was assessed. Statements related to various policy documents were categorized according to document types, substance in the documents, and timing in the policy process. Results: Various policy documents were spontaneously mentioned by 33 of 50 interviewees, in eight of nine case studies, and in all stages of the policy process. Well-defined statements concerning which content in the policy documents that actually impacted on the policy process development were uncommon. Conclusions: This study shows that policy documents are present in policy processes related to child health-promoting activities in Swedish municipalities. As Swedish municipalities are autonomous and not forced to pursue governmental recommendations, this probably demonstrates that policy documents are significant in the development of such processes.
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23.
  • Guldbrandsson, Karin, 1956, et al. (författare)
  • What makes things happen? : An analysis of the development of nine health-promoting measures aimed at children and adolescents in three Swedish municipalities
  • 2005
  • Ingår i: Social Science & Medicine. - 0277-9536. ; 61:11, dec, s. 2331-2344
  • Tidskriftsartikel (refereegranskat)abstract
    • The Swedish municipalities offer important environments for health promotion. However, national actors need increased knowledge on how to support the development of public health measures in the municipalities. The aims of this study were to describe the development of municipal health-promoting measures directed at children and adolescents and to identify factors that might explain the development of such measures. Fifty semi-structured interviews and written documentation gathered from three municipalities in Stockholm County resulted in nine case studies. A policy process matrix, based on the actor-structural approach, was constructed to categorise the data. Five aspects contributing to the trajectory of municipal health-promoting measures aimed at children and adolescents were often mentioned in the data set. These are financial problems, perceived local needs, access to external funding, statements in national and international policy documents and the presence of a local public health sector. Politicians, public officials, and non-governmental organisations were the most mentioned actors, with heavy commitment, professional skills, and powerful position referred to as prevalent characteristics. Public health core concepts such as epidemiological statistics and evidence-based measures were rarely mentioned. The health care sector did not seem to have had any direct influence on municipal health-promoting measures. The dissemination of knowledge about public health related international and national policy documents and support for the institutionalisation of a local public health sector might be useful ways to support municipal public health measures.
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24.
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25.
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26.
  • Gustafsson, Helen, et al. (författare)
  • MAGIC-type polymer gel for three-dimensional dosimetry: intensity-modulated radiation therapy verification.
  • 2003
  • Ingår i: Medical Physics. - : Wiley. - 0094-2405. ; 30:6, s. 1264-1271
  • Tidskriftsartikel (refereegranskat)abstract
    • A new type of polymer gel dosimeter, which responds well to absorbed dose even when manufactured in the presence of normal levels of oxygen, was recently described by Fong et al. [Phys. Med. Biol. 46, 3105-3113 (2001)] and referred to by the acronym MAGIC. The aim of this study was to investigate the feasibility of using this new type of gel for intensity-modulated radiation therapy (IMRT) verification. Gel manufacturing was carried out in room atmosphere under normal levels of oxygen. IMRT inverse treatment planning was performed using the Helios software. The gel was irradiated using a linear accelerator equipped with a dynamic multileaf collimator, and intensity modulation was achieved using sliding window technique. The response to absorbed dose was evaluated using magnetic resonance imaging. Measured and calculated dose distributions were compared with regard to in-plane isodoses and dose volume histograms. In addition, the spatial and dosimetric accuracy was evaluated using the gamma formalism. Good agreement between calculated and measured data was obtained. In the isocenter plane, the 70% and 90% isodoses acquired using the different methods are mostly within 2 mm, with up to 3 mm disagreement at isolated points. For the planning target volume (PTV), the calculated mean relative dose was 96.8 +/- 2.5% (1 SD) and the measured relative mean dose was 98.6 +/- 2.2%. Corresponding data for an organ at risk was 34.4 +/- 0.9% and 32.7 +/- 0.7%, respectively. The gamma criterion (3 mm spatial/3% dose deviation) was fulfilled for 94% of the pixels in the target region. Discrepancies were found in hot spots the upper and lower parts of the PTV, where the measured dose was up to 11% higher than calculated. This was attributed to sub optimal scatter kernels used in the treatment planning system dose calculations. Our results indicate great potential for IMRT verification using MAGIC-type polymer gel.
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27.
  • Haraldsson, André, et al. (författare)
  • A Helical tomotherapy as a robust low-dose treatment alternative for total skin irradiation
  • 2019
  • Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 20:5, s. 44-54
  • Tidskriftsartikel (refereegranskat)abstract
    • Mycosis fungoides is a disease with manifestation of the skin that has traditionally been treated with electron therapy. In this paper, we present a method of treating the entire skin with megavoltage photons using helical tomotherapy (HT), verified through a phantom study and clinical dosimetric data from our first two treated patients. A whole body phantom was fitted with a wetsuit as bolus, and scanned with computer tomography. We accounted for variations in daily setup using virtual bolus in the treatment plan optimization. Positioning robustness was tested by moving the phantom, and recalculating the dose at different positions. Patient treatments were verified with in vivo film dosimetry and dose reconstruction from daily imaging. Reconstruction of the actual delivered dose to the patients showed similar target dose as the robustness test of the phantom shifted 10 mm in all directions, indicating an appropriate approximation of the anticipated setup variation. In vivo film measurements agreed well with the calculated dose confirming the choice of both virtual and physical bolus parameters. Despite the complexity of the treatment, HT was shown to be a robust and feasible technique for total skin irradiation. We believe that this technique can provide a viable option for Tomotherapy centers without electron beam capability.
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28.
  • Haraldsson, André, et al. (författare)
  • Implementing safe and robust Total Marrow Irradiation using Helical Tomotherapy – A practical guide
  • 2019
  • Ingår i: Physica Medica. - : Elsevier BV. - 1120-1797. ; 60, s. 162-167
  • Tidskriftsartikel (refereegranskat)abstract
    • Total Marrow Irradiation (TMI) with Helical Tomotherapy is a radiotherapy treatment technique that targets bone marrow and sanctuary sites prior to stem cell or bone marrow transplantation (SCT/BMT). TMI is a complex procedure that involves several critical steps that all need to be carefully addressed for a successful implementation, such as dose homogeneity in field junctions, choice of target margins, integrity of treatment and back-up planning. In this work we present our solution for a robust and reproducible workflow throughout the treatment chain and data for twenty-three patients treated to date. Material & Methods: Patients were immobilized in a whole body vacuum cushion and thermoplastic mask. CT-scanning and treatment were performed in two parts with field matching at the upper thigh. Target consisted of marrow containing bone and sanctuary sites. Lungs, kidneys, bowel, heart and liver were defined as organs at risk (OAR). A fast surface scanning system was used to position parts of the body not covered by the imaging system (MVCT) as well as to reduce treatment time. Results: All patients completed their treatment and could proceed with SCT/BMT. Doses to OARs were significantly reduced and target dose homogeneity was improved compared to TBI. Robustness tests performed on field matching and patient positioning support that the field junction technique is adequate. Replacing MVCT with optical surface scanning reduced the treatment time by 25 min per fraction. Conclusion: The methodology presented here has shown to provide a safe, robust and reproducible treatment for Total Marrow Irradiation using Tomotherapy.
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29.
  • Haraldsson, André, et al. (författare)
  • Organ sparing total marrow irradiation compared to total body irradiation prior to allogeneic stem cell transplantation
  • 2021
  • Ingår i: European Journal of Haematology. - : Wiley. - 0902-4441 .- 1600-0609. ; 107:4, s. 393-407
  • Tidskriftsartikel (refereegranskat)abstract
    • Objectives: Total body irradiation (TBI) is commonly used prior to hematopoietic stem cell transplantation (HSCT) in myeloablative conditioning regimens. However, TBI may be replaced by total marrow irradiation (TMI) at centres with access to Helical TomoTherapy, a modality that has the advantage of delivering intensity-modulated radiotherapy to long targets such as the entire bone marrow compartment. Toxicity after organ sparing TMI prior to HSCT has not previously been reported compared to TBI or with regard to engraftment data. Methods: We conducted a prospective observational study on 37 patients that received organ sparing TMI prior to HSCT and compared this cohort to retrospective data on 33 patients that received TBI prior to HSCT. Results: The 1-year graft-versus-host disease-free, relapse-free survival (GRFS) was 67.5% for all patients treated with TMI and 80.5% for patients with matched unrelated donor and treated with TMI, which was a significant difference from historical data on TBI patients with a hazard ratio of 0.45 (P =.03) and 0.24 (P <.01). Engraftment with a platelet count over 20 [K/µL] and 50 [K/µL] was significantly shorter for the TMI group, and neutrophil recovery was satisfactory in both treatment cohorts. There was generally a low occurrence of other treatment-related toxicities. Conclusions: Despite small cohorts, some significant differences were found; TMI as part of the myeloablative conditioning yields a high 1-year GRFS, fast and robust engraftment, and low occurrence of acute toxicity.
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30.
  • Haraldsson, André, et al. (författare)
  • Surface-guided tomotherapy improves positioning and reduces treatment time : A retrospective analysis of 16 835 treatment fractions
  • 2020
  • Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 21:8, s. 139-148
  • Tidskriftsartikel (refereegranskat)abstract
    • Purpose: In this study, we have quantified the setup deviation and time gain when using fast surface scanning for daily setup/positioning with weekly megavoltage computed tomography (MVCT) and compared it to daily MVCT. Methods: A total of 16 835 treatment fractions were analyzed, treated, and positioned using our TomoTherapy HD (Accuray Inc., Madison, USA) installed with a Sentinel optical surface scanning system (C-RAD Positioning AB, Uppsala, Sweden). Patients were positioned using in-room lasers, surface scanning and MVCT for the first three fractions. For the remaining fractions, in-room laser was used for setup followed by daily surface scanning with MVCT once weekly. The three-dimensional (3D) setup correction for surface scanning was evaluated from the registration between MVCT and the planning CT. The setup correction vector for the in-room lasers was assessed from the surface scanning and the MVCT to planning CT registration. The imaging time was evaluated as the time from imaging start to beam-on. Results: We analyzed 894 TomoTherapy treatment plans from 2012 to 2018. Of all the treatment fractions performed with surface scanning, 90 % of the residual errors were within 2.3 mm for CNS (N = 284), 2.9 mm for H&N (N = 254), 8.7 mm for thorax (N = 144) and 10.9 for abdomen (N = 134) patients. The difference in residual error between surface scanning and positioning with in-room lasers was significant (P < 0.005) for all sites. The imaging time was assessed as total imaging time per treatment plan, modality, and treatment site and found that surface scanning significantly reduced patient on-couch time compared to MVCT for all treatment sites (P < 0.005). Conclusions: The results indicate that daily surface scanning with weekly MVCT can be used with the current target margins for H&N, CNS, and thorax, with reduced imaging time.
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31.
  • Hill, Brendan, et al. (författare)
  • Investigation and analysis of ferrous sulfate polyvinyl alcohol (PVA) gel dosimeter
  • 2002
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 47:23, s. 4233-4246
  • Tidskriftsartikel (refereegranskat)abstract
    • Ferrous sulfate (Fe(SO4)2) PVA gels were investigated for a range of absorbed doses up to 20 Gy using both magnetic resonance imaging (MRI) and spectrophotometry to determine R1 and optical density (OD) dose responses and G values. It was found that R1- and OD-dose sensitivities increased with O2 saturation or by the introduction of a freeze-thaw cycle during preparation of the PVA gel. The storage temperature of the Fe(SO4)2 PVA gel at -18 degrees C increased R1-dose sensitivity above that of gels stored at 5 degrees C. The addition of sucrose to the formulation was found to result in the largest increase in both R1- and OD-dose sensitivities. Fe(SO4)2 PVA gel with and without the addition of xylenol orange was demonstrated to have a G value of approximately 20 ions/100 eV and with sucrose approximately 24 ions/100 eV.
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32.
  • Ilkhanizadeh, Shirin, et al. (författare)
  • Live Detection of Neural Progenitors and Glioblastoma Cells by an Oligothiophene Derivative
  • 2023
  • Ingår i: ACS Applied Bio Materials. - : American Chemical Society (ACS). - 2576-6422. ; 6:9, s. 3790-3797
  • Tidskriftsartikel (refereegranskat)abstract
    • There is an urgent need for simple and non-invasive identification of live neural stem/progenitor cells (NSPCs) in the developing and adult brain as well as in disease, such as in brain tumors, due to the potential clinical importance in prognosis, diagnosis, and treatment of diseases of the nervous system. Here, we report a luminescent conjugated oligothiophene (LCO), named p-HTMI, for non-invasive and non-amplified real-time detection of live human patient-derived glioblastoma (GBM) stem cell-like cells and NSPCs. While p-HTMI stained only a small fraction of other cell types investigated, the mere addition of p-HTMI to the cell culture resulted in efficient detection of NSPCs or GBM cells from rodents and humans within minutes. p-HTMI is functionalized with a methylated imidazole moiety resembling the side chain of histidine/histamine, and non-methylated analogues were not functional. Cell sorting experiments of human GBM cells demonstrated that p-HTMI labeled the same cell population as CD271, a proposed marker for stem cell-like cells and rapidly migrating cells in glioblastoma. Our results suggest that the LCO p-HTMI is a versatile tool for immediate and selective detection of neural and glioma stem and progenitor cells.
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33.
  • Jóhannesson, Vilberg, et al. (författare)
  • Adaptive sequential plan-on-plan optimization during prostate-specific antigen response guided radiotherapy of recurrent prostate cancer
  • 2021
  • Ingår i: Physics and imaging in radiation oncology. - : Elsevier BV. - 2405-6316. ; 18, s. 5-10
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Treatment adaptation based on tumour biomarker response during radiotherapy of prostate cancer, could be used for both escalation and de-escalation of radiation doses and volumes. To execute an adaptation involving extension of treatment volumes during radiation can however be restricted by the doses already delivered. The aim of this work was to develop a treatment planning method that addresses this challenge. Material and methods: A volumetric-modulated-arc-therapy (VMAT) planning method with sequential plan-on-plan optimization was developed for a prospective phase II trial including 100 patients on salvage radiotherapy (SRT) for prostate cancer recurrence. A treatment adaptation was performed after five weeks of SRT based on prostate-specific antigen response during this phase of the treatment. This involved extension of treatment volumes for non-responders (n = 64) to include pelvic lymph nodes and boost to 68Gallium-Prostate-Specific-Membrane-Antigen-Positron-Emission-Tomography positive lesions. This method was evolved by introducing an EQD2 (equivalent dose in 2.0 Gy fractions) correction of the base plan for improved dose coverage. Results: All dose-volume criteria for target coverage were met for the non-responders when based on physical dose. An EQD2 correction of the base plan for non-responders, implemented for the final 29 patients, led to a statistically significant improvement in dose coverage as compared to the 35 patients treated without EQD2 correction. Conclusions: This is to our knowledge the only study presented on biomarker-guided sequential VMAT radiotherapy using a plan-on-plan technique in the pelvis. By using a biologically adapted technique an improved target coverage was achieved without compromising doses to organs at risk.
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34.
  • Johnson, Louis Banka, et al. (författare)
  • Radiation enteropathy and leucocyte-endothelial cell reactions in a refined small bowel model
  • 2004
  • Ingår i: BMC Surgery. - : Springer Science and Business Media LLC. - 1471-2482. ; 4
  • Tidskriftsartikel (refereegranskat)abstract
    • BACKGROUND: Leucocyte recruitment and inflammation are key features of high dose radiation-induced tissue injury. The inflammatory response in the gut may be more pronounced following radiotherapy due to its high bacterial load in comparison to the response in other organs. We designed a model to enable us to study the effects of radiation on leucocyte-endothelium interactions and on intestinal microflora in the murine ileum. This model enables us to study specifically the local effects of radiation therapy. METHOD: A midline laparotomy was performed in male C57/Bl6 mice and a five-centimetre segment of ileum is irradiated using the chamber. Leucocyte responses (rolling and adhesion) were then analysed in ileal venules 2 - 48 hours after high dose irradiation, made possible by an inverted approach using intravital fluorescence microscopy. Furthermore, intestinal microflora, myeloperoxidase (MPO) and cell histology were analysed. RESULTS: The highest and most reproducible increase in leucocyte rolling was exhibited 2 hours after high dose irradiation whereas leucocyte adhesion was greatest after 16 hours. Radiation reduced the intestinal microflora count compared to sham animals with a significant decrease in the aerobic count after 2 hours of radiation. Further, the total aerobic counts, Enterobacteriaceae and Lactobacillus decreased significantly after 16 hours. In the radiation groups, the bacterial count showed a progressive increase from 2 to 24 hours after radiation. CONCLUSION: This study presents a refinement of a previous method of examining mechanisms of radiation enteropathy, and a new approach at investigating radiation induced leucocyte responses in the ileal microcirculation. Radiation induced maximum leucocyte rolling at 2 hours and adhesion peaked at 16 hours. It also reduces the microflora count, which then starts to increase steadily afterwards. This model may be instrumental in developing strategies against pathological recruitment of leucocytes and changes in intestinal microflora in the small bowel after radiotherapy.
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35.
  • Jönsson, Mattias, et al. (författare)
  • Technical evaluation of a laser-based optical surface scanning system for prospective and retrospective breathing adapted computed tomography.
  • 2015
  • Ingår i: Acta Oncologica. - 1651-226X. ; 54:2, s. 261-265
  • Tidskriftsartikel (refereegranskat)abstract
    • Background. For breathing adapted radiotherapy, the same motion monitoring system can be used for imaging and triggering of the accelerator. Purpose. To evaluate a new technique for prospective gated computed tomography (CT) and four-dimensional CT (4DCT) using a laser based surface scanning system (Sentinel(™), C-RAD, Uppsala, Sweden). The system was compared to the AZ-733V respiratory gating system (Anzai Medical, Tokyo, Japan) and the Real-Time Position Management System (RPM(™)) (Varian Medical Systems, Palo Alto, CA, USA). Material and methods. Temporal accuracy was evaluated using a moving phantom programmed to move a platform along trajectories following a sin(6)(ωt) function with amplitudes from 6 to 20 mm and periods from 2 to 5 s during 120 s while the motion was recorded. The recorded data was Fourier transformed and the peak area at the fundamental and harmonic frequencies compared to data generated using the same sinusoidal function. For verification of the 4DCT reconstruction process, the phantom was programmed to move along a sinusoidal trajectory. Ten phase series were reconstructed. The distance from the couch to the platform was measured in each image. By fitting the function sin(ωt-ϕ) to the values measured in the images corresponding to each slice, the phase of each image was verified. Results and conclusion. In the recorded data, the peak area at the fundamental frequency covered on average 104 ± 4%, 102 ± 4% and 91 ± 27% of the peak area in the generated data for the Sentinel(™), RPM(™) and AZ-733V systems, respectively. All systems managed to resolve both harmonic frequencies. The second experiment showed that all images were sorted into the correct series using breathing data recorded by each system. The systems generated very similar results, however, it is preferable to use the same system both for imaging and treatment.
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36.
  • Jönsson, Mattias, et al. (författare)
  • Technical evaluation of different motion-monitoring systems for respiratory gating in radiation therapy
  • 2013
  • Ingår i: Medical Physics in the Baltic States. - 1822-5721. ; , s. 38-41
  • Konferensbidrag (refereegranskat)abstract
    • The purpose of this work was to evaluate three motion-monitoring systems: Sentinel (TM), Catalyst (TM) (both C-RAD) and Real-time Position Management (RPM (TM)) system (Varian Medical Systems Inc) for respiratory gating in radiotherapy. To measure the systems. latency, an in-house built circuit with a microcontroller operating a piston was used. The trigger pulse was sent from the gating systems to the accelerator within 300 mu s. However, the response time of the accelerator could be over 300 ms
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37.
  • Karlsson, Anna, et al. (författare)
  • Dose integration characteristics in normoxic polymer gel dosimetry investigated using sequential beam irradiation
  • 2007
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 52:15, s. 4697-4706
  • Tidskriftsartikel (refereegranskat)abstract
    • Dose integration properties were investigated for normoxic polymer gels based on methacrylic acid (nMAG) and acrylamide/ N, N'-methylenebisacrylamide (nPAG). The effect of sequential irradiation was studied for different fractionation schemes and varying amounts of methacrylic acid for the nMAG gels. Magnetic resonance imaging (MRI) was used for read out of the absorbed dose response. The investigated gels exhibited a dependence on the fractionation scheme. The response when the total dose was divided into fractions of 0.5 Gy was compared with the response when the total dose was delivered in a single fraction. The slope of the R2 versus the absorbed dose response decreased when the absorbed dose per fraction was increased. Also, for higher amounts of methacrylic acid in the nMAG system the difference in the response increased. For gels containing 2, 4, 6 and 8% methacrylic acid, the R2 versus the absorbed dose response increased by 35, 37, 63 and 93%, respectively. Furthermore, the effect of the fractionation was larger when a higher total absorbed dose was given. The effect was less pronounced for the investigated nPAG, containing 3% acrylamide and 3% N, N'-methylenebisacrylamide, than for the nMAG systems. Consequently, this study indicates that the nPAG system has preferable beam integration characteristics compared with the nMAG system.
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38.
  • Konradsson, Elise, et al. (författare)
  • Beam control system and output fine-tuning for safe and precise delivery of FLASH radiotherapy at a clinical linear accelerator
  • 2024
  • Ingår i: Frontiers in Oncology. - 2234-943X. ; 14
  • Tidskriftsartikel (refereegranskat)abstract
    • Introduction: We have previously adapted a clinical linear accelerator (Elekta Precise, Elekta AB) for ultra-high dose rate (UHDR) electron delivery. To enhance reliability in future clinical FLASH radiotherapy trials, the aim of this study was to introduce and evaluate an upgraded beam control system and beam tuning process for safe and precise UHDR delivery. Materials and Methods: The beam control system is designed to interrupt the beam based on 1) a preset number of monitor units (MUs) measured by a monitor detector, 2) a preset number of pulses measured by a pulse-counting diode, or 3) a preset delivery time. For UHDR delivery, an optocoupler facilitates external control of the accelerator’s thyratron trigger pulses. A beam tuning process was established to maximize the output. We assessed the stability of the delivery, and the independent interruption capabilities of the three systems (monitor detector, pulse counter, and timer). Additionally, we explored a novel approach to enhance dosimetric precision in the delivery by synchronizing the trigger pulse with the charging cycle of the pulse forming network (PFN). Results: Improved beam tuning of gun current and magnetron frequency resulted in average dose rates at the dose maximum at isocenter distance of >160 Gy/s or >200 Gy/s, with or without an external monitor chamber in the beam path, respectively. The delivery showed a good repeatability (standard deviation (SD) in total film dose of 2.2%) and reproducibility (SD in film dose of 2.6%). The estimated variation in DPP resulted in an SD of 1.7%. The output in the initial pulse depended on the PFN delay time. Over the course of 50 measurements employing PFN synchronization, the absolute percentage error between the delivered number of MUs calculated by the monitor detector and the preset MUs was 0.8 ± 0.6% (mean ± SD). Conclusion: We present an upgraded beam control system and beam tuning process for safe and stable UHDR electron delivery of hundreds of Gy/s at isocenter distance at a clinical linac. The system can interrupt the beam based on monitor units and utilize PFN synchronization for improved dosimetric precision in the dose delivery, representing an important advancement toward reliable clinical FLASH trials.
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39.
  • Konradsson, Elise, et al. (författare)
  • Correction for Ion Recombination in a Built-in Monitor Chamber of a Clinical Linear Accelerator at Ultra-High Dose Rates
  • 2020
  • Ingår i: Radiation Research. - 0033-7587. ; 194:6, s. 580-586
  • Tidskriftsartikel (refereegranskat)abstract
    • In the novel and promising radiotherapy technique known as FLASH, ultra-high dose-rate electron beams are used. As a step towards clinical trials, dosimetric advances will be required for accurate dose delivery of FLASH. The purpose of this study was to determine whether a built-in transmission chamber of a clinical linear accelerator can be used as a real-Time dosimeter to monitor the delivery of ultra-high-dose-rate electron beams. This was done by modeling the drop-in ion-collection efficiency of the chamber with increasing dose-per-pulse values, so that the ion recombination effect could be considered. The raw transmission chamber signal was extracted from the linear accelerator and its response was measured using radiochromic film at different dose rates/dose-per-pulse values, at a source-To-surface distance of 100 cm. An increase of the polarizing voltage, applied over the transmission chamber, by a factor of 2 and 3, improved the ion-collection efficiency, with corresponding increased efficiency at the highest dose-per-pulse values by a factor 1.4 and 2.2, respectively. The drop-in ion-collection efficiency with increasing dose-per-pulse was accurately modeled using a logistic function fitted to the transmission chamber data. The performance of the model was compared to that of the general theoretical Boag models of ion recombination in ionization chambers. The logistic model was subsequently used to correct for ion recombination at dose rates ranging from conventional to ultra-high, making the transmission chamber useful as a real-Time monitor for the dose delivery of FLASH electron beams in a clinical setup.
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40.
  • Konradsson, Elise, et al. (författare)
  • Establishment and Initial Experience of Clinical FLASH Radiotherapy in Canine Cancer Patients
  • 2021
  • Ingår i: Frontiers in Oncology. - : Frontiers Media SA. - 2234-943X. ; 11
  • Tidskriftsartikel (refereegranskat)abstract
    • FLASH radiotherapy has emerged as a treatment technique with great potential to increase the differential effect between normal tissue toxicity and tumor response compared to conventional radiotherapy. To evaluate the feasibility of FLASH radiotherapy in a relevant clinical setting, we have commenced a feasibility and safety study of FLASH radiotherapy in canine cancer patients with spontaneous superficial solid tumors or microscopic residual disease, using the electron beam of our modified clinical linear accelerator. The setup for FLASH radiotherapy was established using a short electron applicator with a nominal source-to-surface distance of 70 cm and custom-made Cerrobend blocks for collimation. The beam was characterized by measuring dose profiles and depth dose curves for various field sizes. Ten canine cancer patients were included in this initial study; seven patients with nine solid superficial tumors and three patients with microscopic disease. The administered dose ranged from 15 to 35 Gy. To ensure correct delivery of the prescribed dose, film measurements were performed prior to and during treatment, and a Farmer-type ion-chamber was used for monitoring. Treatments were found to be feasible, with partial response, complete response or stable disease recorded in 11/13 irradiated tumors. Adverse events observed at follow-up ranging from 3-6 months were mild and consisted of local alopecia, leukotricia, dry desquamation, mild erythema or swelling. One patient receiving a 35 Gy dose to the nasal planum, had a grade 3 skin adverse event. Dosimetric procedures, safety and an efficient clincal workflow for FLASH radiotherapy was established. The experience from this initial study will be used as a basis for a veterinary phase I/II clinical trial with more specific patient inclusion selection, and subsequently for human trials.
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41.
  • Konradsson, Elise, et al. (författare)
  • Evaluation of intensity-modulated electron FLASH radiotherapy in a clinical setting using veterinary cases
  • 2023
  • Ingår i: Medical Physics. - 0094-2405. ; 50:10, s. 6569-6579
  • Tidskriftsartikel (refereegranskat)abstract
    • Purpose: The increased normal tissue tolerance for FLASH radiotherapy (FLASH-RT), as compared to conventional radiotherapy, was first observed in ultra-high dose rate electron beams. Initial clinical trials in companion animals have revealed a high risk of developing osteoradionecrosis following high-dose single-fraction electron FLASH-RT, which may be related to inhomogeneities in the dose distribution. In the current study, we aim to evaluate the possibilities of intensity-modulated electron FLASH-RT in a clinical setting to ensure a homogeneous dose distribution in future veterinary and human clinical trials. Methods: Our beam model in the treatment planning system electronRT (.decimal, LLC, Sanford, FL, USA) was based on a 10-MeV electron beam from a clinical linear accelerator used to treat veterinary patients with FLASH-RT in a clinical setting. In electronRT, the beam can be intensity-modulated using tungsten island blocks in the electron block cutout, and range-modulated using a customized bolus with variable thickness. Modulations were first validated in a heterogeneous phantom by comparing measured and calculated dose distributions. To evaluate the impact of intensity modulation in superficial single-fraction FLASH-RT, a treatment planning study was conducted, including eight canine cancer patient cases with simulated tumors in the head-and-neck region. For each case, treatment plans with and without intensity modulation were created for a uniform bolus and a range-modulating bolus. Treatment plans were evaluated using a target dose homogeneity index (HI), a conformity index (CI), the near-maximum dose outside the target ((Figure presented.)), and the near-minimum dose to the target ((Figure presented.)). Results: By adding intensity modulation to plans with a uniform bolus, the HI could be improved (p = 0.017). The combination of a range-modulating bolus and intensity modulation provided a further significant improvement of the HI as compared to using intensity modulation in combination with a uniform bolus (p = 0.036). The range-modulating bolus also improved the CI compared to using a uniform bolus, both with an open beam (p = 0.046) and with intensity modulation (p = 0.018), as well as increased the (Figure presented.) (p = 0.036 with open beam and p = 0.05 with intensity modulation) and reduced the median (Figure presented.) (not significant). Conclusions: By using intensity-modulated electron FLASH-RT in combination with range-modulating bolus, the target dose homogeneity and conformity in canine patients with simulated tumors in complex areas in the head-and-neck region could be improved. By utilizing this technique, we hope to decrease the dose outside the target volume and avoid hot spots in future clinical electron FLASH-RT studies, thereby reducing the risk of radiation-induced toxicity.
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42.
  • Konradsson, Elise, et al. (författare)
  • Reconfiguring a Plane-Parallel Transmission Ionization Chamber to Extend the Operating Range into the Ultra-High Dose-per-pulse Regime
  • 2024
  • Ingår i: Radiation Research. - 0033-7587. ; 201:3, s. 252-260
  • Tidskriftsartikel (refereegranskat)abstract
    • This study aims to investigate the feasibility of enhancing the charge collection efficiency (CCE) of a transmission chamber by reconfiguring its design and operation. The goal was to extend the range of dose-per-pulse (DPP) values with no or minimal recombination effects up to the ultra-high dose rate (UHDR) regime. The response of two transmission chambers, with electrode distance of 1 mm and 0.6 mm, respectively, was investigated as a function of applied voltage. The chambers were mounted one-by-one in the electron applicator of a 10 MeV FLASH-modified clinical linear accelerator. The chamber signals were measured as a function of nominal DPP, which was determined at the depth of dose maximum using EBT-XD film in solid water and ranged from 0.6 mGy per pulse to 0.9 Gy per pulse, for both the standard voltage of 320 V and the highest possible safe voltage of 1,200 V. The CCE was calculated and fitted with an empirical logistic function that incorporated the electrode distance and the chamber voltage. The CCE decreased with increased DPP. The CCE at the highest achievable DPP was 24% (36%) at 320 V and 51% (82%) at 1,200 V, for chambers with 1 mm (0.6 mm) electrode distance. For the combination of 1,200 V- and 0.6-mm electrode distance, the CCE was»100% for average dose rate up to 70 Gy/s at the depth of dose maximum in the phantom at a source-to-surface distance of 100 cm. Our findings indicate that minor modifications to a plane-parallel transmission chamber can substantially enhance the CCE and extending the chamber's operating range to the UHDR regime. This supports the potential of using transmission chamber-based monitoring solutions for UHDR beams, which could facilitate the delivery of UHDR treatments using an approach similar to conventional clinical delivery.
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43.
  • Kristensson, Elias, et al. (författare)
  • Quantification of the absorbed dose in 3D by means of advanced optical diagnostics based on structured illumination
  • 2015
  • Ingår i: 8th International Conference on 3D Radiation Dosimetry (IC3DDOSE). - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 573, s. 012010-012010
  • Konferensbidrag (refereegranskat)abstract
    • The purpose of this study was to present a novel optical diagnostic tool that corrects for undesired contribution of multiply scattered light, thus opening up for e.g. quantitative optical CT measurements of opaque samples. The approach is based on a technique called Structured Illumination (SI), which is commonly employed within microscopic imaging to enhance the depth-resolution. The concept of SI applies for many types of source-detector arrangements and the configuration employed in this paper relies on side-scattering detection. A nPAG polymer gel phantom was irradiated using 6 MV beam. Three-dimensional information was obtained by translating the sample perpendicular to the direction of light, thus sequentially probing different sections. These were then stacked together to form a 3D representation of the sample. By altering the polarization of the laser light during the data acquisition it was discovered that the aggregates responsible for the scattering of light followed Rayleigh scattering, implying that their individual sizes are smaller than, or in the order of, 500 nm.
  •  
44.
  • Kügele, Malin, et al. (författare)
  • Surface guided radiotherapy (SGRT) improves breast cancer patient setup accuracy
  • 2019
  • Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; , s. 61-68
  • Tidskriftsartikel (refereegranskat)abstract
    • Purpose: The purpose of the study was to investigate if surface guided radiotherapy (SGRT) can decrease setup deviations for tangential and locoregional breast cancer patients compared to conventional laser-based setup (LBS). Materials and Methods: Both tangential (63 patients) and locoregional (76 patients) breast cancer patients were enrolled in this study. For LBS, the patients were positioned by aligning skin markers to the room lasers. For the surface based setup (SBS), an optical surface scanning system was used for daily setup using both single and three camera systems. To compare the two setup methods, the patient position was evaluated using verification imaging (field images or orthogonal images). Results: For both tangential and locoregional treatments, SBS decreased the setup deviation significantly compared to LBS (P < 0.01). For patients receiving tangential treatment, 95% of the treatment sessions were within the clinical tolerance of ≤ 4 mm in any direction (lateral, longitudinal or vertical) using SBS, compared to 84% for LBS. Corresponding values for patients receiving locoregional treatment were 70% and 54% for SBS and LBS, respectively. No significant difference was observed comparing the setup result using a single camera system or a three camera system. Conclusions: Conventional laser-based setup can with advantage be replaced by surface based setup. Daily SGRT improves patient setup without additional imaging dose to breast cancer patients regardless if a single or three camera system was used.
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45.
  • Larsson Callerfelt, Anna-Karin, et al. (författare)
  • Specific mediator inhibition by the NO donors SNP and NCX 2057 in the peripheral lung: implications for allergen-induced bronchoconstriction.
  • 2009
  • Ingår i: Respiratory Research. - : Springer Science and Business Media LLC. - 1465-9921 .- 1465-993X. ; 10:Jun 4
  • Tidskriftsartikel (refereegranskat)abstract
    • BACKGROUND: The aim of this study was to examine potential therapeutic effect of the two NO donors NCX 2057 (3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid) 4-(nitrooxy)butyl ester) and SNP (sodium nitroprusside) on the early allergic airway response in the peripheral lung. METHODS: The experiments were performed in guinea pig lung parenchyma (GPLP) derived from ovalbumin (OVA) sensitized guinea pigs. The effects of NCX 2057 and SNP were evaluated by contractile responses and mediator release during OVA challenge. The generation of nitrite and nitrate was assessed by chemiluminescence. Statistical analysis was evaluated by ANOVA. RESULTS: Cumulatively increasing concentrations of OVA (1-10,000 ng/ml) induced concentration-dependent contractions of the GPLP that were reduced by NCX 2057 (100 microM, p < 0.001) and SNP (100 microM, p < 0.05). Antigen-induced eicosanoid release was decreased by NCX 2057 (100 microM, p < 0.001) but not by SNP (100 microM), whereas the release of histamine was reduced by SNP (100 microM, p < 0.001) but not by NCX 2057 (100 microM). In addition, NCX 2057 (0.1-100 microM), but not SNP (0.1-100 microM), relaxed leukotriene D4 (10 nM) precontracted GPLP (p < 0.01). The guanylyl cyclase inhibitor ODQ had no effect on the NCX 2057 mediated relaxation. SNP released significantly less nitrite than NCX 2057. CONCLUSION: Although both SNP and NCX 2057 reduced the release of pro-inflammatory mediators, their profiles were distinctly different. Furthermore, NCX 2057 also induced smooth muscle dilation in the GPLP. The findings point to specific anti-inflammatory effects of different NO donors in the peripheral lung tissue.
  •  
46.
  • Larsson, Lena Gunvor, et al. (författare)
  • A national study on collaboration in care planning for patients with complex needs
  • 2019
  • Ingår i: International Journal of Health Planning and Management. - : Wiley. - 0749-6753 .- 1099-1751. ; 34:1, s. E646-E660
  • Tidskriftsartikel (refereegranskat)abstract
    • INTRODUCTION: The purpose of this study was to investigate inter-organisational collaboration on care planning for patients with complex care needs. Internationally, and in Sweden where the data for this study was collected, difficulties in care planning and transition of patients between the main health care providers, hospitals, municipal care, and primary care are well known.METHOD: A survey of a total population of care managers in hospitals, municipalities, and primary care in Sweden was conducted. The study assessed accessibility, willingness, trustworthiness, and collaboration between health care providers. Data were analysed with descriptive statistics, bivariate, and multivariate regressions.RESULTS: The results indicate that Swedish health care providers show strong self-awareness, but they describe each other's ability to collaborate as weak. Primary care stands out, displaying the highest discrepancy between self-awareness and displayed accessibility, willingness, trustworthiness, and collaboration.CONCLUSION: Inability to collaborate in patient care planning may be due to shortcomings in terms of trust between caregivers in the health care organisation at a national level. Organisations that experience difficulties in collaboration tend to defend themselves with arguments about their own excellence and insufficiency of others.
  •  
47.
  • Larsson, Lena Gunvor, et al. (författare)
  • Primary care managers’ perceptions of their capability in providing care planning to patients with complex needs
  • 2017
  • Ingår i: Health Policy. - : Elsevier BV. - 0168-8510 .- 1872-6054. ; 121:1, s. 58-65
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study was to investigate primary care managers’ perceptions of their capability in providing care planning to patients with complex needs. Care planning is defined as a process where the patient, family and health professionals engage in dialogue about the patient's care needs and plan care interventions together. Methods Semi-structured interviews with 18 primary care managers in western Sweden were conducted using Westrin's theoretical cooperation model. Data were analysed using a qualitative deductive method. Main findings Results reveal that the managers’ approach to care planning was dominated by non-cooperation and separation. The managers were permeated by uncertainty about the meaning of the task of care planning as such. They did not seem to be familiar with the national legislation stipulating that every healthcare provider must meet patients’ need for care interventions and participate in the care planning. Implications for practice To accomplish care planning, the process needs to cross – and overcome – both professional and organisational boundaries. There is also a need for incentives to develop working methods that promote local cooperation in order to facilitate optimal care for patients with complex needs.
  •  
48.
  • Lempart, Michael, et al. (författare)
  • Modifying a clinical linear accelerator for delivery of ultra-high dose rate irradiation
  • 2019
  • Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 0167-8140. ; 139, s. 40-45
  • Tidskriftsartikel (refereegranskat)abstract
    • Objectives: The purpose of this study was to modify a clinical linear accelerator, making it capable of electron beam ultra-high dose rate (FLASH) irradiation. Modifications had to be quick, reversible, and without interfering with clinical treatments. Methods: Performed modifications: (1) reduced distance with three setup positions, (2) adjusted/optimized gun current, modulator charge rate and beam steering values for a high dose rate, (3) delivery was controlled with a microcontroller on an electron pulse level, and (4) moving the primary and/or secondary scattering foils from the beam path. Results: The variation in dose for a five-pulse delivery was measured to be 1% (using a diode, 4% using film) during 10 minutes after a warm-up procedure, later increasing to 7% (11% using film). A FLASH irradiation dose rate was reached at the cross-hair foil, MLC, and wedge position, with ≥30, ≥80, and ≥300 Gy/s, respectively. Moving the scattering foils resulted in an increased output of ≥120, ≥250, and ≥1000 Gy/s, at the three positions. The beam flatness was 5% at the cross-hair position for a 20 × 20 and a 10 × 10 cm2 area, with and without both scattering foils in the beam. The beam flatness was 10% at the wedge position for a 6 and 2.5 cm diametric area, with and without the scattering foils in the beam path. Conclusions: A clinical accelerator was modified to produce ultra-high dose rates, high enough for FLASH irradiation. Future work aims to fine-tune the dose delivery, using the on-board transmission chamber signal and adjusting the dose-per-pulse.
  •  
49.
  • Lempart, Michael, et al. (författare)
  • Volumetric modulated arc therapy dose prediction and deliverable treatment plan generation for prostate cancer patients using a densely connected deep learning model
  • 2021
  • Ingår i: Physics and imaging in radiation oncology. - : Elsevier BV. - 2405-6316. ; 19, s. 112-119
  • Tidskriftsartikel (refereegranskat)abstract
    • Background and purpose: Radiation therapy treatment planning is a manual, time-consuming task that might be accelerated using machine learning algorithms. In this study, we aimed to evaluate if a triplet-based deep learning model can predict volumetric modulated arc therapy (VMAT) dose distributions for prostate cancer patients. Materials and methods: A modified U-Net was trained on triplets, a combination of three consecutive image slices and corresponding segmentations, from 160 patients, and compared to a baseline U-Net. Dose predictions from 17 test patients were transformed into deliverable treatment plans using a novel planning workflow. Results: The model achieved a mean absolute dose error of 1.3%, 1.9%, 1.0% and ≤ 2.6% for clinical target volume (CTV) CTV_D100%, planning target volume (PTV) PTV_D98%, PTV_D95% and organs at risk (OAR) respectively, when compared to the clinical ground truth (GT) dose distributions. All predicted distributions were successfully transformed into deliverable treatment plans and tested on a phantom, resulting in a passing rate of 100% (global gamma, 3%, 2 mm, 15% cutoff). The dose difference between deliverable treatment plans and GT dose distributions was within 4.4%. The difference between the baseline model and our improved model was statistically significant (p < 0.05) for CVT_D100%, PTV_D98% and PTV_D95%. Conclusion: Triplet-based training improved VMAT dose distribution predictions when compared to 2D. Dose predictions were successfully transformed into deliverable treatment plans using our proposed treatment planning procedure. Our method may automate parts of the workflow for external beam prostate radiation therapy and improve the overall treatment speed and plan quality.
  •  
50.
  • Lepag, M, et al. (författare)
  • Dose resolution optimization of polymer gel dosimeters using different monomers
  • 2001
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 46:10, s. 2665-2680
  • Tidskriftsartikel (refereegranskat)abstract
    • Polymer gel dosimeters of different formulations were manufactured from different monomers of acrylamide, acrylic acid, methacrylic acid, 1-vinyl-2-pyrrolidinone, 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate. Gelatin and agarose were used as the gelling agents and N,N'-methylene-bis-acrylamide was used as a co-monomer in each polymer gel dosimeter. The T2 dependence of each dosimeter was analysed using a model of fast exchange of magnetization. The influence of the half-dose and the apparent T2 of the polymer-proton pool on the dose resolution (Dpdelta) were examined. Comparisons are made with the commonly employed R2-dose sensitivity. Differences exist suggesting that experiments reported in the literature using what were thought to be more optimal dosimeters may not actually be so. Based on Dpdelta of each formulation, conclusions are drawn on the optimal formulation required for a specific range of absorbed doses. In addition, information about the extent of polymerization of the monomers used along with some characteristics of the polymer network formed are reported. The influence of the concentration of monomers and gelling agent was subsequently evaluated using a model of fast exchange of magnetization. Based on these calculations, further improvement in Dpdelta can be expected.
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