| 1. |
- Adolfsson, Emelie, et al.
(författare)
-
Measurement of absorbed dose to water around an electronic brachytherapy source : Comparison of two dosimetry systems: lithium formate EPR dosimeters and radiochromic EBT2 film
- 2015
-
Ingår i: Physics in Medicine and Biology. - : Institute of Physics Publishing (IOPP). - 0031-9155 .- 1361-6560. ; 60:9, s. 3869-3882
-
Tidskriftsartikel (refereegranskat)abstract
- Interest in high dose rate (HDR) electronic brachytherapy operating at 50 kV is increasing. For quality assurance it is important to identify dosimetry systems that can measure the absorbed doses in absolute terms which is difficult in this energy region. In this work a comparison is made between two dosimetry systems, EPR lithium formate dosimeters and radiochromic EBT2 film.Both types of dosimeters were irradiated simultaneously in a PMMA phantom using the Axxent EBS. Absorbed dose to water was determined at distances of 10 mm, 30 mm and 50 mm from the EBS. Results were traceable to different primary standards as regards to absorbed dose to water (EPR) and air kerma (EBT2). Monte Carlo simulations were used in absolute terms as a third estimate of absorbed dose to water.Agreement within the estimated expanded (k = 2) uncertainties (5% (EPR), 7% (EBT2)) was found between the results at 30 mm and 50 mm from the x-ray source. The same result was obtained in 4 repetitions of irradiation, indicating high precision in the measurements with both systems. At all distances, agreement between EPR and Monte Carlo simulations was shown as was also the case for the film measurements at 30mm and 50mm. At 10mm the geometry for the film measurements caused too large uncertainty in measured values depending on the exact position (within sub-mm distances) of the EBS and the 10 mm film results were exculded from comparison.This work has demonstrated good performance of the lithium formate EPR dosimetry system in accordance with earlier experiments at higher photon energies (192Ir HDR brachytherapy). It was also highlighted that there might be issues regarding the energy dependence and intrinsic efficiency of the EBT2 film that need to be considered for measurements using low energy sources.
|
|
| 2. |
- Holm, Åsa, et al.
(författare)
-
Heuristics for Integrated Optimization of Catheter Positioning and Dwell Time Distribution in Prostate HDR Brachytherapy
- 2016
-
Ingår i: Annals of Operations Research. - : Springer. - 0254-5330 .- 1572-9338. ; 236:2, s. 319-339
-
Tidskriftsartikel (refereegranskat)abstract
- High dose-rate (HDR) brachytherapy is a kind of radiotherapy used to treat, among others, prostate cancer. When applied to prostate cancer a radioactive source is moved through catheters implanted into the prostate. For each patient a treatment plan is constructed that decide for example catheter placement and dwell time distribution, that is where to stop the radioactive source and for how long.Mathematical optimization methods has been used to find quality plans with respect to dwell time distribution, however few optimization approaches regarding catheter placement have been studied. In this article we present an integrated optimization model that optimize catheter placement and dwell time distribution simultaneously. Our results show that integrating the two decisions yields greatly improved plans, from 15% to 94% improvement.Since the presented model is computationally demanding to solve we also present three heuristics: tabu search, variable neighbourhood search and genetic algorithm. Of these variable neighbourhood search is clearly the best, outperforming a state-of-the-art optimization software (CPLEX) and the two other heuristics.
|
|
| 3. |
- Kaveckyte, Vaiva, et al.
(författare)
-
Suitability of microDiamond detectors for the determination of absorbed dose to water around high-dose-rate Ir-192 brachytherapy sources
- 2018
-
Ingår i: Medical physics (Lancaster). - : WILEY. - 0094-2405 .- 2473-4209. ; 45:1, s. 429-437
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: Experimental dosimetry of high-dose-rate (HDR) Ir-192 brachytherapy (BT) sources is complicated due to high dose and dose-rate gradients, and softening of photon energy spectrum with depth. A single crystal synthetic diamond detector microDiamond (PTW 60019, Freiburg, Germany) has a small active volume, high sensitivity, direct readout, and nearly water-equivalent active volume. The purpose of this study was to evaluate the suitability of microDiamond detectors for the determination of absorbed dose to water around HDR Ir-192 BT sources. Three microDiamond detectors were used, allowing for the comparison of their properties. Methods: In-phantom measurements were performed using microSelectron and VariSource iX HDR Ir-192 BT treatment units. Their treatment planning systems (TPSs), Oncentra (v. 4.3) and BrachyVision (v. 13.6), respectively, were used to create irradiation plans for a cubic PMMA phantom with the microDiamond positioned at one of three source-to-detector distances (SDDs) (1.5, 2.5, and 5.5 cm) at a time. The source was stepped in increments of 0.5 cm over a total length of 6 cm to yield absorbed dose of 2 Gy at the nominal reference-point of the detector. Detectors were calibrated in Co-60 beam in terms of absorbed dose to water, and Monte Carlo (MC) calculated beam quality correction factors were applied to account for absorbed-dose energy dependence. Phantom correction factors were applied to account for differences in dimensions between the measurement phantom and a water phantom used for absorbed dose calculations made with a TPS. The same measurements were made with all three of the detectors. Additionally, dose-rate dependence and stability of the detectors were evaluated in Co-60 beam. Results: The percentage differences between experimentally determined and TPS-calculated absorbed doses to water were from -1.3% to +2.9%. The values agreed to within experimental uncertainties, which were from 1.9% to 4.3% (k = 2) depending on the detector, SDD and treatment delivery unit. No dose-rate or intrinsic energy dependence corrections were applied. All microDiamonds were comparable in terms of preirradiation dose, stability of the readings and energy response, and showed a good agreement. Conclusions: The results indicate that the microDiamond is potentially suitable for the determination of absorbed dose to water around HDR Ir-192 BT sources and may be used for independent verification of TPSs calculations, as well as for QA measurements of HDR Ir-192 BT treatment delivery units at clinical sites. (C) 2017 American Association of Physicists in Medicine
|
|
| 4. |
- Magnusson, Maria, et al.
(författare)
-
DIRA-3D-a model-based iterative algorithm for accurate dual-energy dual-source 3D helical CT
- 2019
-
Ingår i: Biomedical Engineering & Physics Express. - : IOP PUBLISHING LTD. - 2057-1976. ; 5:6
-
Tidskriftsartikel (refereegranskat)abstract
- Quantitative dual-energy computed tomography may improve the accuracy of treatment planning in radiation therapy. Of special interest are algorithms that can estimate material composition of the imaged object. One example of such an algorithm is the 2D model-based iterative reconstruction algorithm DIRA. The aim of this work is to extend this algorithm to 3D so that it can be used with cone-beams and helical scanning. In the new algorithm, the parallel FBP method was replaced with the approximate 3D FBP-based PI-method. Its performance was tested using a mathematical phantom consisting of six ellipsoids. The algorithm substantially reduced the beam-hardening artefact and the artefacts caused by approximate reconstruction after six iterations. Compared to Alvarez-Macovskis base material decomposition, DIRA-3D does not require geometrically consistent projections and hence can be used in dual-source CT scanners. Also, it can use several tissue-specific material bases at the same time to represent the imaged object.
|
|
| 5. |
- Adolfsson, Emelie, et al.
(författare)
-
END-TO-END AUDIT: COMPARISON OF TLD AND LITHIUM FORMATE EPR DOSIMETRY
- 2019
-
Ingår i: Radiation Protection Dosimetry. - : OXFORD UNIV PRESS. - 0144-8420 .- 1742-3406. ; 186:1, s. 119-122
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to test two different solid state dosimetry systems for the purpose of end-to-end audits of radiotherapy volumetric modulated arc therapy (VMAT) technique; a lithium formate electron paramagnetic resonance system and a lithium fluoride thermoluminescent dosimetry system. As a complement to the solid state systems, ion chamber measurements were performed. A polystyrene phantom with a planning target volume (PTV) and an organ at risk (OAR) structure was scanned using CT. A VMAT dose plan was optimized to deliver 2 Gy to the target volume and to minimize the dose to the OAR. The different detectors were inserted into the phantom and the planned dose distribution was delivered. The measured doses were compared to the treatment planning system (TPS) calculated doses. Good agreement was found between the TPS calculated and the measured doses, well accepted for the dose determinations in remote dosimetry audits of VMAT treatment technique.
|
|
| 6. |
- Ahnesjö, Anders, 1953-, et al.
(författare)
-
Collapsed cone dose calculations for heterogeneous tissues in brachytherapy using primary and scatter separation source data
- 2017
-
Ingår i: Computer Methods and Programs in Biomedicine. - : ELSEVIER IRELAND LTD. - 0169-2607 .- 1872-7565. ; 139, s. 17-29
-
Tidskriftsartikel (refereegranskat)abstract
- Background and Objective: Brachytherapy is a form of radiation therapy using sealed radiation sources inserted within or in the vicinity of the tumor of, e.g., gynecological, prostate or head and neck cancers. Accurate dose calculation is a crucial part of the treatment planning. Several reviews have called for clinical software with model-based algorithms that better take into account the effects of patient individual distribution of tissues, source-channel and shielding attenuation than the commonly employed TG-43 formalism which simply map homogeneous water dose distributions onto the patient. In this paper we give a comprehensive and thorough derivation of such an algorithm based on collapsed cone point-kernel superposition, and describe details of its implementation into a commercial treatment planning system for clinical use. Methods: A brachytherapy version of the collapsed-cone algorithm using analytical raytraces of the primary photon radiation followed by successive scattering dose calculation for once and multiply scattered photons is described in detail, including derivation of the corresponding set of recursive equations for energy transport along cone axes/transport lines and the coupling to clinical source modeling. Specific implementation issues for setting up of the calculation grid, handling of intravoxel gradients and voxels partly containing non patient applicator material are given. Results: Sample runs for two clinical cases are shown, one being a gynecological application with a tungsten-shielded applicator and one a breast implant. These two cases demonstrate the impact of improved dose calculation versus TG-43 formalism. Conclusions: Use of model-based dose calculation algorithms for brachytherapy taking the three-dimensional treatment geometry into account increases the dosimetric accuracy in planning and follow up of treatments. The comprehensive description and derivations provided gives a rigid background for further clinical, educational and research applications.
|
|
| 7. |
- Ballester, Facundo, et al.
(författare)
-
A generic high-dose rate Ir-192 brachytherapy source for evaluation of model-based dose calculations beyond the TG-43 formalism
- 2015
-
Ingår i: Medical physics (Lancaster). - : American Association of Physicists in Medicine: Medical Physics. - 0094-2405. ; 42:6, s. 3048-3062
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: In order to facilitate a smooth transition for brachytherapy dose calculations from the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) formalism to model-based dose calculation algorithms (MBDCAs), treatment planning systems (TPSs) using a MBDCA require a set of well-defined test case plans characterized by Monte Carlo (MC) methods. This also permits direct dose comparison to TG-43 reference data. Such test case plans should be made available for use in the software commissioning process performed by clinical end users. To this end, a hypothetical, generic high-dose rate (HDR) Ir-192 source and a virtual water phantom were designed, which can be imported into a TPS. Methods: A hypothetical, generic HDR Ir-192 source was designed based on commercially available sources as well as a virtual, cubic water phantom that can be imported into any TPS in DICOM format. The dose distribution of the generic Ir-192 source when placed at the center of the cubic phantom, and away from the center under altered scatter conditions, was evaluated using two commercial MBDCAs [Oncentra (R) Brachy with advanced collapsed-cone engine (ACE) and BrachyVision AcuRos (TM)]. Dose comparisons were performed using state-of-the-art MC codes for radiation transport, including ALGEBRA, BrachyDose, GEANT4, MCNP5, MCNP6, and pENELopE2008. The methodologies adhered to recommendations in the AAPM TG-229 report on high-energy brachytherapy source dosimetry. TG-43 dosimetry parameters, an along-away dose-rate table, and primary and scatter separated (PSS) data were obtained. The virtual water phantom of (201)(3) voxels (1 mm sides) was used to evaluate the calculated dose distributions. Two test case plans involving a single position of the generic HDR Ir-192 source in this phantom were prepared: (i) source centered in the phantom and (ii) source displaced 7 cm laterally from the center. Datasets were independently produced by different investigators. MC results were then compared against dose calculated using TG-43 and MBDCA methods. Results: TG-43 and PSS datasets were generated for the generic source, the PSS data for use with the ACE algorithm. The dose-rate constant values obtained from seven MC simulations, performed independently using different codes, were in excellent agreement, yielding an average of 1.1109 +/- 0.0004 cGy/(h U) (k = 1, Type A uncertainty). MC calculated dose-rate distributions for the two plans were also found to be in excellent agreement, with differences within type A uncertainties. Differences between commercial MBDCA and MC results were test, position, and calculation parameter dependent. On average, however, these differences were within 1% for ACUROS and 2% for ACE at clinically relevant distances. Conclusions: A hypothetical, generic HDR Ir-192 source was designed and implemented in two commercially available TPSs employing different MBDCAs. Reference dose distributions for this source were benchmarked and used for the evaluation of MBDCA calculations employing a virtual, cubic water phantom in the form of a CT DICOM image series. The implementation of a generic source of identical design in all TPSs using MBDCAs is an important step toward supporting univocal commissioning procedures and direct comparisons between TPSs. (C) 2015 American Association of Physicists in Medicine.
|
|
| 8. |
- Candela-Juan, C., et al.
(författare)
-
Dosimetric characterization of two radium sources for retrospective dosimetry studies
- 2015
-
Ingår i: Medical physics (Lancaster). - : American Association of Physicists in Medicine: Medical Physics. - 0094-2405 .- 2473-4209. ; 42:5, s. 2132-2142
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: During the first part of the 20th century, Ra-226 was the most used radionuclide for brachytherapy. Retrospective accurate dosimetry, coupled with patient follow up, is important for advancing knowledge on long-term radiation effects. The purpose of this work was to dosimetrically characterize two Ra-226 sources, commonly used in Sweden during the first half of the 20th century, for retrospective dose-effect studies. Methods: An 8 mg Ra-226 tube and a 10 mg Ra-226 needle, used at Radiumhemmet (Karolinska University Hospital, Stockholm, Sweden), from 1925 to the 1960s, were modeled in two independent Monte Carlo (MC) radiation transport codes: GEANT4 and MCNP5. Absorbed dose and collision kerma around the two sources were obtained, from which the TG-43 parameters were derived for the secular equilibrium state. Furthermore, results from this dosimetric formalism were compared with results from a MC simulation with a superficial mould constituted by five needles inside a glass casing, placed over a water phantom, trying to mimic a typical clinical setup. Calculated absorbed doses using the TG-43 formalism were also compared with previously reported measurements and calculations based on the Sievert integral. Finally, the dose rate at large distances from a Ra-226 point-like-source placed in the center of 1 m radius water sphere was calculated with GEANT4. Results: TG-43 parameters [including gL(r), F(r,theta), Lambda, and s(K)] have been uploaded in spreadsheets as additional material, and the fitting parameters of a mathematical curve that provides the dose rate between 10 and 60 cm from the source have been provided. Results from TG-43 formalism are consistent within the treatment volume with those of a MC simulation of a typical clinical scenario. Comparisons with reported measurements made with thermoluminescent dosimeters show differences up to 13% along the transverse axis of the radium needle. It has been estimated that the uncertainty associated to the absorbed dose within the treatment volume is 10%-15%, whereas uncertainty of absorbed dose to distant organs is roughly 20%-25%. Conclusions: The results provided here facilitate retrospective dosimetry studies of Ra-226 using modern treatment planning systems, which may be used to improve knowledge on long term radiation effects. It is surely important for the epidemiologic studies to be aware of the estimated uncertainty provided here before extracting their conclusions.
|
|
| 9. |
- Carlsson Tedgren, Åsa, et al.
(författare)
-
The collapsed cone algorithm for Ir-192 dosimetry using phantom-size adaptive multiple-scatter point kernels
- 2015
-
Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 60:13, s. 5313-5323
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to investigate how dose distributions calculated with the collapsed cone (CC) algorithm depend on the size of the water phantom used in deriving the point kernel for multiple scatter. A research version of the CC algorithm equipped with a set of selectable point kernels for multiple-scatter dose that had initially been derived in water phantoms of various dimensions was used. The new point kernels were generated using EGSnrc in spherical water phantoms of radii 5 cm, 7.5 cm, 10 cm, 15 cm, 20 cm, 30 cm and 50 cm. Dose distributions derived with CC in water phantoms of different dimensions and in a CT-based clinical breast geometry were compared to Monte Carlo (MC) simulations using the Geant4-based brachytherapy specific MC code Algebra. Agreement with MC within 1% was obtained when the dimensions of the phantom used to derive the multiple-scatter kernel were similar to those of the calculation phantom. Doses are overestimated at phantom edges when kernels are derived in larger phantoms and underestimated when derived in smaller phantoms (by around 2% to 7% depending on distance from source and phantom dimensions). CC agrees well with MC in the high dose region of a breast implant and is superior to TG43 in determining skin doses for all multiple-scatter point kernel sizes. Increased agreement between CC and MC is achieved when the point kernel is comparable to breast dimensions. The investigated approximation in multiple scatter dose depends on the choice of point kernel in relation to phantom size and yields a significant fraction of the total dose only at distances of several centimeters from a source/implant which correspond to volumes of low doses. The current implementation of the CC algorithm utilizes a point kernel derived in a comparatively large (radius 20 cm) water phantom. A fixed point kernel leads to predictable behaviour of the algorithm with the worst case being a source/implant located well within a patient/phantom for which low doses at phantom edges can be overestimated by 2-5 %. It would be possible to improve the situation by using a point kernel for multiple-scatter dose adapted to the patient/phantom dimensions at hand.
|
|
| 10. |
- Ghazal, Mohammed, et al.
(författare)
-
6-MV small field output factors: intra-/intermachine comparison and implementation of TRS-483 using various detectors and several linear accelerators
- 2019
-
Ingår i: Medical physics (Lancaster). - : WILEY. - 0094-2405 .- 2473-4209. ; 46:11, s. 5350-5359
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose To investigate the applicability of output correction factors reported in TRS-483 on 6-MV small-field detector-reading ratios using four solid-state detectors. Also, to investigate variations in 6-MV small-field output factors (OF) among nominally matched linear accelerators (linacs). Methods The TRS-483 Code of Practice (CoP) introduced and provided output correction factors to be applied to measured detector-reading ratios to obtain OFs for several small-field detectors. Detector readings for 0.5 cm x 0.5 cm to 8 cm x 8 cm fields were measured and normalized to that of 10 cm x 10 cm field giving the detector-reading ratios. Three silicon diodes, IBA PFD, IBA EFD (IBA, Schwarzenbruck, Germany), PTW T60017, and one microdiamond, PTW T60019 (PTW, Freiburg, Germany), were used. Output correction factors from the CoP were applied to measured detector-reading ratios. Measurements were performed on six Clinac and six TrueBeam linacs (Varian Medical Systems, Palo Alto, USA). An investigation of the relationship between the size of small fields and corresponding detector-reading ratio among the linacs was performed by measuring lateral dose profiles for 0.5 cm x 0.5 cm fields to determine the full width half maximum (FWHM). The relationship between the linacs focal spot size and the small-field detector-reading ratio was investigated by measuring 10 cm x 10 cm lateral dose profiles and determining the penumbra width reflecting the focal spot size. Measurement geometry was as follows: gantry angle = 0 degrees, collimator angle = 0 degrees, source-to surface distance (SSD) = 90 cm, and depth in water = 10 cm. Results For a given linac and 0.5 cm x 0.5 cm field, the deviations in detector-reading ratios among the detectors were 9%-15% for the Clinacs and 4%-5% for the TrueBeams. Use of output correction factors reduced these deviations to 6%-12% and 3%-4%, respectively. For field sizes equal to or larger than 0.8 cm x 0.8 cm, the deviations were corrected to 1% using output correction factors for both Clinacs and TrueBeams. For a given detector and 0.5 cm x 0.5 cm field, the deviations in detector-reading ratios among the linacs were 11%-17% for the Clinacs and 5-6% for the TrueBeams. For 1 cm x 1 cm the deviations were 1%-2% for Clinacs and 1% for TrueBeams. For field sizes larger than 1 cm x 1 cm the deviations were within 1% for both Clinacs and TrueBeams. No relationship between FWHMs and detector-reading ratios for 0.5 cm x 0.5 cm was observed. For Clinacs, larger 10 cm x 10 cm penumbra width yielded lower 0.5 cm x 0.5 cm detector-reading ratio indicating an effect of the focal spot size. For TrueBeams, the spread of penumbra widths was lower compared to Clinacs and no similar relationship was observed. Conclusions Output correction factors from the TRS-483 CoP are not sufficient for accurate determination of OF for 0.5 cm x 0.5 cm fields but are applicable for 0.8 cm x 0.8 cm to 8 cm x 8 cm fields. Nominally matched Clinacs and TrueBeams show large differences in detector-reading ratios for fields smaller than 1 cm x 1 cm.
|
|
| 11. |
- Lindborg, Lennart, et al.
(författare)
-
Nanodosimetry and RBE values in radiotherapy
- 2015
-
Ingår i: Radiation Protection Dosimetry. - : OXFORD UNIV PRESS. - 0144-8420 .- 1742-3406. ; 166:1-4, s. 339-342
-
Tidskriftsartikel (refereegranskat)abstract
- In a recent paper, the authors reported that the dose mean lineal energy, (y) over bar (D) in a volume of about 10-15 nm is approximately proportional to the alpha-parameter in the linear-quadratic relation used in fractionated radiotherapy in both low- and high-LET beams. This was concluded after analyses of reported radiation weighting factors, W-isoE (clinical RBE values), and (y) over bar (D) values in a large range of volumes. Usually, microdosimetry measurements in the nanometer range are difficult; therefore, model calculations become necessary. In this paper, the authors discuss the calculation method. A combination of condensed history Monte Carlo and track structure techniques for calculation of mean lineal energy values turned out to be quite useful. Briefly, the method consists in weighting the relative dose fractions of the primary and secondary charged particles with their respective energy-dependent dose mean lineal energies. The latter were obtained using a large database of Monte Carlo track structure calculations.
|
|
| 12. |
- Lundell, Marie, et al.
(författare)
-
New dosimetry for childhood skin hemangioma treatments with Ra-226 needles or tubes
- 2015
-
Ingår i: Radiotherapy and Oncology. - : ELSEVIER IRELAND LTD. - 0167-8140 .- 1879-0887. ; 116:1, s. 139-142
-
Tidskriftsartikel (refereegranskat)abstract
- Background: The Stockholm Hemangioma Cohort is important for evaluation of late effects after exposure to ionizing radiation during childhood. Dose estimates in this cohort were based on both measurements and calculations using an old treatment planning system. Methods: We compare previously published and calculated dose estimates with new ones, obtained by Monte Carlo simulations, which mimic the hemangioma treatments with Ra-226 needles and tubes. The distances between the Ra-226 sources and the thyroid and breasts, respectively, were reassessed. Result:. The Monte Carlo calculations showed significantly lower dose values than those obtained earlier. The differences depended both on the modeling of the sources and on further individualized distances from the sources. The mean value of the new calculated doses was 25% of the old breast doses and 46% of the old thyroid doses. Conclusion: New dosimetry for hemangioma treatments gives significantly lower organ doses for the few cases receiving the highest absorbed dose values. This implies that radiation risk estimates will increase and have to be recalculated. For retrospective studies it is now possible to calculate organ doses from radium treatments using modern treatment planning systems by modeling the source geometry carefully and apply the TG-43 formalism. It is important to be aware of the large uncertainties in calculated absorbed dose values.
|
|
| 13. |
- Ma, Yunzhi, et al.
(författare)
-
A generic TG-186 shielded applicator for commissioning model-based dose calculation algorithms for high-dose-rate Ir-192 brachytherapy
- 2017
-
Ingår i: Medical physics (Lancaster). - : WILEY. - 0094-2405 .- 2473-4209. ; 44:11, s. 5961-5976
-
Tidskriftsartikel (refereegranskat)abstract
- PurposeA joint working group was created by the American Association of Physicists in Medicine (AAPM), the European Society for Radiotherapy and Oncology (ESTRO), and the Australasian Brachytherapy Group (ABG) with the charge, among others, to develop a set of well-defined test case plans and perform calculations and comparisons with model-based dose calculation algorithms (MBDCAs). Its main goal is to facilitate a smooth transition from the AAPM Task Group No. 43 (TG-43) dose calculation formalism, widely being used in clinical practice for brachytherapy, to the one proposed by Task Group No. 186 (TG-186) for MBDCAs. To do so, in this work a hypothetical, generic high-dose rate (HDR) Ir-192 shielded applicator has been designed and benchmarked. MethodsA generic HDR Ir-192 shielded applicator was designed based on three commercially available gynecological applicators as well as a virtual cubic water phantom that can be imported into any DICOM-RT compatible treatment planning system (TPS). The absorbed dose distribution around the applicator with the TG-186 Ir-192 source located at one dwell position at its center was computed using two commercial TPSs incorporating MBDCAs (Oncentra((R)) Brachy with Advanced Collapsed-cone Engine, ACE, and BrachyVision ACUROS) and state-of-the-art Monte Carlo (MC) codes, including ALGEBRA, BrachyDose, egs_brachy, Geant4, MCNP6, and Penelope2008. TPS-based volumetric dose distributions for the previously reported source centered in water and source displaced test cases, and the new source centered in applicator test case, were analyzed here using the MCNP6 dose distribution as a reference. Volumetric dose comparisons of TPS results against results for the other MC codes were also performed. Distributions of local and global dose difference ratios are reported. ResultsThe local dose differences among MC codes are comparable to the statistical uncertainties of the reference datasets for the source centered in water and source displaced test cases and for the clinically relevant part of the unshielded volume in the source centered in applicator case. Larger local differences appear in the shielded volume or at large distances. Considering clinically relevant regions, global dose differences are smaller than the local ones. The most disadvantageous case for the MBDCAs is the one including the shielded applicator. In this case, ACUROS agrees with MC within [-4.2%, +4.2%] for the majority of voxels (95%) while presenting dose differences within [-0.12%, +0.12%] of the dose at a clinically relevant reference point. For ACE, 95% of the total volume presents differences with respect to MC in the range [-1.7%, +0.4%] of the dose at the reference point. ConclusionsThe combination of the generic source and generic shielded applicator, together with the previously developed test cases and reference datasets (available in the Brachytherapy Source Registry), lay a solid foundation in supporting uniform commissioning procedures and direct comparisons among treatment planning systems for HDR Ir-192 brachytherapy.
|
|
| 14. |
- Morén, Björn, 1987-, et al.
(författare)
-
A mathematical optimization model for spatial adjustments of dose distributions in high dose-rate brachytherapy
- 2019
-
Ingår i: Physics in Medicine and Biology. - : IOP PUBLISHING LTD. - 0031-9155 .- 1361-6560. ; 64:22
-
Tidskriftsartikel (refereegranskat)abstract
- High dose-rate brachytherapy is a modality of radiation therapy used for cancer treatment, in which the radiation source is placed within the body. The treatment goal is to give a high enough dose to the tumour while sparing nearby healthy tissue and organs (organs-at-risk). The most common criteria for evaluating dose distributions are dosimetric indices. For the tumour, such an index is the portion of the volume that receives at least a specified dose level (e.g. the prescription dose), while for organs-at-risk it is instead the portion of the volume that receives at most a specified dose level. Dosimetric indices are aggregate criteria and do not consider spatial properties of the dose distribution. Further, there are neither any established evaluation criteria for characterizing spatial properties, nor have such properties been studied in the context of mathematical optimization of brachytherapy. Spatial properties are however of clinical relevance and therefore dose plans are sometimes adjusted manually to improve them. We propose an optimization model for reducing the prevalence of contiguous volumes with a too high dose (hot spots) or a too low dose (cold spots) in a tentative dose plan. This model is independent of the process of constructing the tentative plan. We conduct computational experiments with tentative plans obtained both from optimization models and from clinical practice. The objective function considers pairs of dose points and each pair is given a distance-based penalty if the dose is either too high or too low at both dose points. Constraints are included to retain dosimetric indices at acceptable levels. Our model is designed to automate the manual adjustment step in the planning process. In the automatic adjustment step large-scale optimization models are solved. We show reductions of the volumes of the largest hot and cold spots, and the computing times are feasible in clinical practice.
|
|
| 15. |
- Morén, Björn, 1987-, et al.
(författare)
-
An extended dose-volume model in high dose-rate brachytherapy : Using mean-tail-dose to reduce tumor underdosage
- 2019
-
Ingår i: Medical physics (Lancaster). - : Wiley-Blackwell Publishing Inc.. - 0094-2405 .- 2473-4209. ; 46:6, s. 2556-2566
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose High dose-rate brachytherapy is a method of radiotherapy for cancer treatment in which the radiation source is placed within the body. In addition to give a high enough dose to a tumor, it is also important to spare nearby healthy organs [organs at risk (OAR)]. Dose plans are commonly evaluated using the so-called dosimetric indices; for the tumor, the portion of the structure that receives a sufficiently high dose is calculated, while for OAR it is instead the portion of the structure that receives a sufficiently low dose that is of interest. Models that include dosimetric indices are referred to as dose-volume models (DVMs) and have received much interest recently. Such models do not take the dose to the coldest (least irradiated) volume of the tumor into account, which is a distinct weakness since research indicates that the treatment effect can be largely impaired by tumor underdosage even to small volumes. Therefore, our aim is to extend a DVM to also consider the dose to the coldest volume. Methods An improved DVM for dose planning is proposed. In addition to optimizing with respect to dosimetric indices, this model also takes mean dose to the coldest volume of the tumor into account. Results Our extended model has been evaluated against a standard DVM in ten prostate geometries. Our results show that the dose to the coldest volume could be increased, while also computing times for the dose planning were improved. Conclusion While the proposed model yields dose plans similar to other models in most aspects, it fulfils its purpose of increasing the dose to cold tumor volumes. An additional benefit is shorter solution times, and especially for clinically relevant times (of minutes) we show major improvements in tumour dosimetric indices.
|
|
| 16. |
- Morén, Björn, 1987-
(författare)
-
Mathematical Modelling of Dose Planning in High Dose-Rate Brachytherapy
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cancer is a widespread type of diseases that each year affects millions of people. It is mainly treated by chemotherapy, surgery or radiation therapy, or a combination of them. One modality of radiation therapy is high dose-rate brachytherapy, used in treatment of for example prostate cancer and gynecologic cancer. Brachytherapy is an invasive treatment in which catheters (hollow needles) or applicators are used to place the highly active radiation source close to or within a tumour.The treatment planning problem, which can be modelled as a mathematical optimization problem, is the topic of this thesis. The treatment planning includes decisions on how many catheters to use and where to place them as well as the dwell times for the radiation source. There are multiple aims with the treatment and these are primarily to give the tumour a radiation dose that is sufficiently high and to give the surrounding healthy tissue and organs (organs at risk) a dose that is sufficiently low. Because these aims are in conflict, modelling the treatment planning gives optimization problems which essentially are multiobjective.To evaluate treatment plans, a concept called dosimetric indices is commonly used and they constitute an essential part of the clinical treatment guidelines. For the tumour, the portion of the volume that receives at least a specified dose is of interest while for an organ at risk it is rather the portion of the volume that receives at most a specified dose. The dosimetric indices are derived from the dose-volume histogram, which for each dose level shows the corresponding dosimetric index. Dose-volume histograms are commonly used to visualise the three-dimensional dose distribution.The research focus of this thesis is mathematical modelling of the treatment planning and properties of optimization models explicitly including dosimetric indices, which the clinical treatment guidelines are based on. Modelling dosimetric indices explicitly yields mixedinteger programs which are computationally demanding to solve. The computing time of the treatment planning is of clinical relevance as the planning is typically conducted while the patient is under anaesthesia. Research topics in this thesis include both studying properties of models, extending and improving models, and developing new optimization models to be able to take more aspects into account in the treatment planning.There are several advantages of using mathematical optimization for treatment planning in comparison to manual planning. First, the treatment planning phase can be shortened compared to the time consuming manual planning. Secondly, also the quality of treatment plans can be improved by using optimization models and algorithms, for example by considering more of the clinically relevant aspects. Finally, with the use of optimization algorithms the requirements of experience and skill level for the planners are lower.This thesis summary contains a literature review over optimization models for treatment planning, including the catheter placement problem. How optimization models consider the multiobjective nature of the treatment planning problem is also discussed.
|
|
| 17. |
- Morén, Björn, 1987-, et al.
(författare)
-
Mathematical optimization of high dose-rate brachytherapy-derivation of a linear penalty model from a dose-volume model
- 2018
-
Ingår i: Physics in Medicine and Biology. - : IOP PUBLISHING LTD. - 0031-9155 .- 1361-6560. ; 63:6
-
Tidskriftsartikel (refereegranskat)abstract
- High dose-rate brachytherapy is a method for cancer treatment where the radiation source is placed within the body, inside or close to a tumour. For dose planning, mathematical optimization techniques are being used in practice and the most common approach is to use a linear model which penalizes deviations from specified dose limits for the tumour and for nearby organs. This linear penalty model is easy to solve, but its weakness lies in the poor correlation of its objective value and the dose-volume objectives that are used clinically to evaluate dose distributions. Furthermore, the model contains parameters that have no clear clinical interpretation. Another approach for dose planning is to solve mixed-integer optimization models with explicit dose-volume constraints which include parameters that directly correspond to dose-volume objectives, and which are therefore tangible. The two mentioned models take the overall goals for dose planning into account in fundamentally different ways. We show that there is, however, a mathematical relationship between them by deriving a linear penalty model from a dose-volume model. This relationship has not been established before and improves the understanding of the linear penalty model. In particular, the parameters of the linear penalty model can be interpreted as dual variables in the dose-volume model.
|
|
| 18. |
- Morén, Björn, 1987-, et al.
(författare)
-
Preventing Hot Spots in High Dose-Rate Brachytherapy
- 2018
-
Ingår i: Operations Research Proceedings 2017. - Cham : Springer International Publishing. - 9783319899190 - 9783319899206 ; , s. 369-375
-
Konferensbidrag (refereegranskat)abstract
- High dose-rate brachytherapy is a method of radiation cancer treatment, where the radiation source is placed inside the body. The recommended way to evaluate dose plans is based on dosimetric indices which are aggregate measures of the received dose. Insufficient spatial distribution of the dose may however result in hot spots, which are contiguous volumes in the tumour that receive a dose that is much too high. We use mathematical optimization to adjust a dose plan that is acceptable with respect to dosimetric indices to also take spatial distribution of the dose into account. This results in large-scale nonlinear mixed-binary models that are solved using nonlinear approximations. We show that there are substantial degrees of freedom in the dose planning even though the levels of dosimetric indices are maintained, and that it is possible to improve a dose plan with respect to its spatial properties.
|
|
| 19. |
- Paiva Fonseca, Gabriel, et al.
(författare)
-
Dose specification for Ir-192 high dose rate brachytherapy in terms of dose-to-water-in-medium and dose-to-medium-in-medium
- 2015
-
Ingår i: Physics in Medicine and Biology. - : IOP Publishing: Hybrid Open Access. - 0031-9155 .- 1361-6560. ; 60:11, s. 4565-4579
-
Tidskriftsartikel (refereegranskat)abstract
- Dose calculation in high dose rate brachytherapy with Ir-192 is usually based on the TG-43U1 protocol where all media are considered to be water. Several dose calculation algorithms have been developed that are capable of handling heterogeneities with two possibilities to report dose: dose-to-medium-inmedium (D-m,D-m) and dose-to-water-in-medium (D-w,D-m). The relation between D-m,D-m and D-w,D-m for Ir-192 is the main goal of this study, in particular the dependence of D-w,D-m on the dose calculation approach using either large cavity theory (LCT) or small cavity theory (SCT). A head and neck case was selected due to the presence of media with a large range of atomic numbers relevant to tissues and mass densities such as air, soft tissues and bone interfaces. This case was simulated using a Monte Carlo (MC) code to score: D-m,D-m, D-w,D-m (LCT), mean photon energy and photon fluence. D-w,D-m (SCT) was derived from MC simulations using the ratio between the unrestricted collisional stopping power of the actual medium and water. Differences between D-m,D-m and D-w,D-m (SCT or LCT) can be negligible (less than1%) for some tissues e.g. muscle and significant for other tissues with differences of up to 14% for bone. Using SCT or LCT approaches leads to differences between D-w,D-m (SCT) and D-w,D-m (LCT) up to 29% for bone and 36% for teeth. The mean photon energy distribution ranges from 222 keV up to 356 keV. However, results obtained using mean photon energies are not equivalent to the ones obtained using the full, local photon spectrum. This work concludes that it is essential that brachytherapy studies clearly report the dose quantity. It further shows that while differences between D-m,D-m and D-w,D-m (SCT) mainly depend on tissue type, differences between D-m,D-m and D-w,D-m (LCT) are, in addition, significantly dependent on the local photon energy fluence spectrum which varies with distance to implanted sources.
|
|
| 20. |
- Perez-Calatayud, Jose, et al.
(författare)
-
GEC-ESTRO ACROP recommendations on calibration and traceability of LE-LDR photon-emitting brachytherapy sources at the hospital level
- 2019
-
Ingår i: Radiotherapy and Oncology. - : ELSEVIER IRELAND LTD. - 0167-8140 .- 1879-0887. ; 135, s. 120-129
-
Tidskriftsartikel (refereegranskat)abstract
- Prostate brachytherapy treatment using permanent implantation of low-energy (LE) low-dose rate (LDR) sources is successfully and widely applied in Europe. In addition, seeds are used in other tumour sites, such as ophthalmic tumours, implanted temporarily. The calibration issues for LE-LDR photon emitting sources are specific and different from other sources used in brachytherapy. In this report, the BRAPHYQS (BRAchytherapy PHYsics Quality assurance System) working group of GEC-ESTRO, has developed the present recommendations to assure harmonized and high-quality seed calibration in European clinics. There are practical aspects for which a clarification/procedure is needed, including aspects not specifically accounted for in currently existing AAPM and ESTRO societal recommendations. The aim of this report has been to provide a European wide standard in LE-LDR source calibration at end-user level, in order to keep brachytherapy treatments with high safety and quality levels. The recommendations herein reflect the guidance to the ESTRO brachytherapy users and describe the procedures in a clinic or hospital to ensure the correct calibration of LE-LDR seeds. (C) 2019 The Authors. Published by Elsevier B.V.
|
|
| 21. |
- Persson, Maria, et al.
(författare)
-
Experience of using MOSFET detectors for dose verification measurements in an end-to-end Ir-192 brachytherapy quality assurance system
- 2018
-
Ingår i: Brachytherapy. - : ELSEVIER SCIENCE INC. - 1538-4721 .- 1873-1449. ; 17:1, s. 227-233
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: Establishment of an end-to-end system for the brachytherapy (BT) dosimetric chain could be valuable in clinical quality assurance. Here, the development of such a system using MOSFET (metal oxide semiconductor field effect transistor) detectors and experience gained during 2 years of use are reported with focus on the performance of the MOSFET detectors. METHODS AND MATERIALS: A bolus phantom was constructed with two implants, mimicking prostate and head amp; neck treatments, using steel needles and plastic catheters to guide the Ir-192 source and house the MOSFET detectors. The phantom was taken through the BT treatment chain from image acquisition to dose evaluation. During the 2-year evaluation-period, delivered doses were verified a total of 56 times using MOSFET detectors which had been calibrated in an external Co-60 beam. An initial experimental investigation on beam quality differences between Ir-192 and Co-60 is reported. RESULTS: The standard deviation in repeated MOSFET measurements was below 3% in the six measurement points with dose levels above 2 Gy. MOSFET measurements overestimated treatment planning system doses by 2-7%. Distance-dependent experimental beam quality correction factors derived in a phantom of similar size as that used for end-to-end tests applied on a time-resolved measurement improved the agreement. CONCLUSIONS: MOSFET detectors provide values stable over time and function well for use as detectors for end-to-end quality assurance purposes in 192Ir BT. Beam quality correction factors should address not only distance from source but also phantom dimensions. (C) 2017 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.
|
|
| 22. |
- Quast, Ulrich, et al.
(författare)
-
A brachytherapy photon radiation quality index Q(BT) for probe-type dosimetry
- 2016
-
Ingår i: Physica medica (Testo stampato). - : ELSEVIER SCI LTD. - 1120-1797 .- 1724-191X. ; 32:6, s. 741-748
-
Tidskriftsartikel (refereegranskat)abstract
- Introduction: In photon brachytherapy (BT), experimental dosimetry is needed to verify treatment plans if planning algorithms neglect varying attenuation, absorption or scattering conditions. The detectors response is energy dependent, including the detector material to water dose ratio and the intrinsic mechanisms. The local mean photon energy E(r) must be known or another equivalent energy quality parameter used. We propose the brachytherapy photon radiation quality index Q(BT) ((E) over bar), to characterize the photon radiation quality in view of measurements of distributions of the absorbed dose to water, D-w, around BT sources. Materials and methods: While the external photon beam radiotherapy (EBRT) radiation quality index Q(EBRT) ((E) over bar) = TPR1020((E) over bar) is not applicable to BT, the authors have applied a novel energy dependent parameter, called brachytherapy photon radiation quality index, defined as Q(BT) ((E) over bar) = D-prim(r = 2 cm; theta(0) = 90 degrees)/D-prim(r(0) = 1 cm; theta(0) = 90 degrees), utilizing precise primary absorbed dose data, D-prim, from source reference databases, without additional MC-calculations. Results and discussion: For BT photon sources used clinically, Q(BT) ((E) over bar) enables to determine the effective mean linear attenuation coefficient (mu) over bar (E) and thus the effective energy of the primary photons E-prim(eff)(r(0), theta(0)) at the TG-43 reference position P-ref (r(0) = 1 cm; theta(0) = 90 degrees) being close to the mean total photon energy (E) over bar (tot)(r(0), theta(0)). If one has calibrated detectors, published (E) over bar (tot)(r) and the BT radiation quality correction factor k(Q, Q0)(BT) ((E) over bar, r, theta) for different BT radiation qualities Q and Q(0), the detectors response can be determined and D-w(r, theta) measured in the vicinity of BT photon sources. Conclusions: This novel brachytherapy photon radiation quality index Q(BT) characterizes sufficiently accurate and precise the primary photon` s penetration probability and scattering potential. (C) 2016 Published by Elsevier Ltd on behalf of Associazione Italiana di Fisica Medica.
|
|
| 23. |
- Wesolowska, Paulina, et al.
(författare)
-
Testing the methodology for a dosimetric end-to-end audit of IMRT/VMAT: results of IAEA multicentre and national studies
- 2019
-
Ingår i: Acta Oncologica. - : TAYLOR & FRANCIS LTD. - 0284-186X .- 1651-226X. ; 58:12, s. 1731-1739
-
Tidskriftsartikel (refereegranskat)abstract
- Introduction: Within an International Atomic Energy Agency (IAEA) co-ordinated research project (CRP), a remote end-to-end dosimetric quality audit for intensity modulated radiation therapy (IMRT)/ volumetric arc therapy (VMAT) was developed to verify the radiotherapy chain including imaging, treatment planning and dose delivery. The methodology as well as the results obtained in a multicentre pilot study and national trial runs conducted in close cooperation with dosimetry audit networks (DANs) of IAEA Member States are presented. Material and methods: A solid polystyrene phantom containing a dosimetry insert with an irregular solid water planning target volume (PTV) and organ at risk (OAR) was designed for this audit. The insert can be preloaded with radiochromic film and four thermoluminescent dosimeters (TLDs). For the audit, radiotherapy centres were asked to scan the phantom, contour the structures, create an IMRT/VMAT treatment plan and irradiate the phantom. The dose prescription was to deliver 4 Gy to the PTV in two fractions and to limit the OAR dose to a maximum of 2.8 Gy. The TLD measured doses and film measured dose distributions were compared with the TPS calculations. Results: Sixteen hospitals from 13 countries and 64 hospitals from 6 countries participated in the multicenter pilot study and in the national runs, respectively. The TLD results for the PTV were all within +/- 5% acceptance limit for the multicentre pilot study, whereas for national runs, 17 participants failed to meet this criterion. All measured doses in the OAR were below the treatment planning constraint. The film analysis identified seven plans in national runs below the 90% passing rate gamma criteria. Conclusion: The results proved that the methodology of the IMRT/VMAT dosimetric end-to-end audit was feasible for its intended purpose, i.e., the phantom design and materials were suitable; the phantom was easy to use and it was robust enough for shipment. Most importantly the audit methodology was capable of identifying suboptimal IMRT/VMAT delivery.
|
|
