| 1. |
- Ceberg, Sofie, et al.
(författare)
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Evaluation of breathing interplay effects during VMAT by using 3D gel measurements
- 2013
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Ingår i: 7th International Conference on 3D Radiation Dosimetry (IC3DDose). - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 444, s. 012098-012098
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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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| 2. |
- Ceberg, Sofie, et al.
(författare)
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Modelling the dynamic dose response of an nMAG polymer gel dosimeter.
- 2012
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 57:15, s. 4845-4853
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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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| 3. |
- Haraldsson, André, et al.
(författare)
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Surface-guided tomotherapy improves positioning and reduces treatment time : A retrospective analysis of 16 835 treatment fractions
- 2020
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Ingår i: Journal of Applied Clinical Medical Physics. - : Wiley. - 1526-9914. ; 21:8, s. 139-148
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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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| 4. |
- Nordström, Fredrik, et al.
(författare)
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3D geometric gel dosimetry verification of intraprostatic fiducial guided hypofractionated radiotherapy of prostate cancer
- 2010
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596. ; 250, s. 287-291
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Konferensbidrag (refereegranskat)abstract
- This pre-study is aimed to investigate the feasibility of a normoxic polyacrylamide gel (nPAG) dosimeter with implanted gold fiducials to evaluate the geometric precision, including setup correction strategies, in the delivery of hypofractionated treatments. For this purpose a phantom consisting of three parts was constructed: (1) the patient simulating volume, providing realistic scatter conditions and weight, (2) a bottle containing the active dosimetric volume and (3) the gold fiducials and the fiducial support structure. A 6.1 Gy prostate IMRT treatment was delivered to the phantom using the sliding-window technique. The phantom was positioned prior to the treatment using the implanted fiducials and kV on-board imaging. An overlay of the 95% isosurface of the TPS calculated dose distribution and the measured dose distribution using gel showed good agreement. The clinical target volume (CTV) was well centred inside the 95% isodose surface of the measured volume. It was shown for the evaluated case that the use of on-board imaging and integrated setup correction tools could be used to compensate for a deliberately introduced offset in CTV position. The study showed that MRI based nPAG gel dosimetry can be used to verify setup correction procedures using implanted gold fiducials.
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| 5. |
- Adrian, Gabriel, et al.
(författare)
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The FLASH effect depends on oxygen concentration
- 2019
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 1748-880X .- 0007-1285. ; 93:1106
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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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| 6. |
- Børresen, Betina, et al.
(författare)
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Evaluation of single-fraction high dose FLASH radiotherapy in a cohort of canine oral cancer patients
- 2023
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Ingår i: Frontiers in Oncology. - 2234-943X. ; 13, s. 1-10
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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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| 7. |
- Gjaldbæk, Bolette W., et al.
(författare)
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Long-term toxicity and efficacy of FLASH radiotherapy in dogs with superficial malignant tumors
- 2024
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Ingår i: Frontiers in Oncology. - 2234-943X. ; 14, s. 01-09
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: FLASH radiotherapy (RT) has emerged as a promising modality, demonstrating both a normal tissue sparing effect and anticancer efficacy. We have previously reported on the safety and efficacy of single fraction FLASH RT in the treatment of oral tumors in canine cancer patients, showing tumor response but also a risk of radiation-induced severe late adverse effects (osteoradionecrosis) for doses ≥35 Gy. Accordingly, the objective in this study was to investigate if single fraction high dose FLASH RT is safe for treating non-oral tumors. Methods: Privately-owned dogs with superficial tumors or microscopic residual disease were included. Treatment was generally delivered as a single fraction of 15-35 Gy 10 MeV electron FLASH RT, although two dogs were re-irradiated at a later timepoint. Follow-up visits were conducted up to 12 months post-treatment to evaluate treatment efficiency and adverse effects. Results: Fourteen dogs with 16 tumors were included, of which nine tumors were treated for gross disease whilst seven tumors were treated post-surgery for microscopic residual disease. Four treatment sites treated with 35 Gy had ulceration post irradiation, which was graded as severe adverse effect. Only mild adverse effects were observed for the remaining treatment sites. None of the patients with microscopic disease experienced recurrence (0/7), and all patients with macroscopic disease showed either a complete (5/9) or a partial response (4/9). Five dogs were euthanized due to clinical disease progression. Discussion: Our study demonstrates that single fraction high dose FLASH RT is generally safe, with few severe adverse effects, particularly in areas less susceptible to radiation-induced damage. In addition, our study indicates that FLASH has anti-tumor efficacy in a clinical setting. No osteoradionecrosis was observed in this study, although other types of high-grade adverse effects including ulcer-formations were observed for the highest delivered dose (35 Gy). Overall, we conclude that osteoradionecrosis following single fraction, high dose FLASH does not appear to be a general problem for non-oral tumor locations. Also, as has been shown previously for oral tumors, 30 Gy appeared to be the maximum safe dose to deliver with single fraction FLASH RT.
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| 8. |
- Konradsson, Elise, et al.
(författare)
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Beam control system and output fine-tuning for safe and precise delivery of FLASH radiotherapy at a clinical linear accelerator
- 2024
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Ingår i: Frontiers in Oncology. - 2234-943X. ; 14
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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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| 9. |
- Konradsson, Elise, et al.
(författare)
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Correction for Ion Recombination in a Built-in Monitor Chamber of a Clinical Linear Accelerator at Ultra-High Dose Rates
- 2020
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Ingår i: Radiation Research. - 0033-7587. ; 194:6, s. 580-586
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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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| 10. |
- Konradsson, Elise, et al.
(författare)
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Establishment and Initial Experience of Clinical FLASH Radiotherapy in Canine Cancer Patients
- 2021
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Ingår i: Frontiers in Oncology. - : Frontiers Media SA. - 2234-943X. ; 11
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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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