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ABSTRACT: Purpose: The purpose of this work is to investigate the importance of heterogeneity corrections for dosimetry in brachytherapy. In particular, we are interested to see how the estimations of the a/b parameter for prostate cancer may change if accurate dose calculations are implemented in brachytherapy. Methods: A Monte Carlo dose engine called ALGEBRA (Based on GEANT4) is used to accurately calculate dose distributions for 30 prostate cancer patients treated with brachytherapy at our institution. The equivalent uniform BED (EUBED) is used to take the high spatial dose heterogeneity of BT into account for estimating the biological efficiency of treatments. For the same level of clinical outcome, the EUBED of BT can be assumed is-effective with BED of external beam radiotherapy to extract the a/b value for prostate cancer. Results: When the heterogeneities are neglected, a/b value equals 3.1 Gy as reported in the literature. When heterogeneities are considered in BT, an a/b value of 5.4 Gy is predicted for prostate cancer. Conclusions: The importance of a precise dosimetry method in plan evaluation has been recognized but its importance on the radiobiological evaluations is usually neglected. This study shows that by using an accurate dosimetry method in BT, the estimation of a/b can change considerably with regard to the reported value of 3.1 Gy in the literature.
Medical Physics 06/2012; 39(6):3996. · 2.83 Impact Factor
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ABSTRACT: Task group 43 (TG43)-based dosimetry algorithms are efficient for brachytherapy dose calculation in water. However, human tissues have chemical compositions and densities different than water. Moreover, the mutual shielding effect of seeds on each other (interseed attenuation) is neglected in the TG43-based dosimetry platforms. The scientific community has expressed the need for an accurate dosimetry platform in brachytherapy. The purpose of this paper is to present ALGEBRA, a Monte Carlo platform for dosimetry in brachytherapy which is sufficiently fast and accurate for clinical and research purposes. ALGEBRA is based on the GEANT4 Monte Carlo code and is capable of handling the DICOM RT standard to recreate a virtual model of the treated site. Here, the performance of ALGEBRA is presented for the special case of LDR brachytherapy in permanent prostate and breast seed implants. However, the algorithm is also capable of handling other treatments such as HDR brachytherapy.
Physics in Medicine and Biology 05/2012; 57(11):3273-80. · 2.83 Impact Factor
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Radiotherapy and Oncology. 05/2011; 99:S59.
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The American Association for Physicists in Medicine (AAPM); 01/2011
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International journal of radiation oncology, biology, physics 11/2010; 78(3):S252-S253. · 4.59 Impact Factor
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Med Phys; 01/2010
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ABSTRACT: Purpose: We assess the impact of the uncertainty of glandular/adipose tissue proportion on dose distribution inside the breast for LDR brachytherapy. Furthermore, we propose a semiautomatic tissue segmentation method to be used in Monte Carlo (MC) calculations for breast LDR patients. Methods & materials: Post‐implant CT exams of five breast brachytherapy patients are imported into our Geant4 MC platform. The CTV and the PTV were contoured by the oncologist; the external contours of the breast, skin, lungs and the ribs were made manually by a physicist. In a first step, the breast is assigned with different proportions of glandular/adipose tissue (ρ = 100/0, 75/25, 50/50, 25/75, 0/100) in order to study the impact of this variation on clinical dosimetries. In a second step, a density‐based semiautomatic segmentation of breast tissue is used to identify glandular from adipose regions inside the breast and to create a more representative breast anatomy with appropriate chemical compositions. A TG43‐like simulation (SMC: Superposition MC) is also performed for each patient. Does‐Volume‐Histograms are used to visualize the effect of dose reduction. Results: In all patients, the glandular/adipose proportion, affects the dose distribution across the breast. The higher the adipose proportion in the breast tissue, the larger is the dose reduction across the organ. The D90 clinical parameter is reduced by up to 22% when the breast is entirely made of adipose. The semiautomatic contouring enabled a patient‐dependent segmentation of the glandular and adipose regions leading to more accurate dose calculations for each patient. Conclusion: Using realistic chemical compositions in MC simulations is achievable for MC calculations. Unlike external‐beam radiotherapy, the low‐energy emission of 103Pd is strongly affected by the heterogeneities adipose proportion in breast. A patient‐dependant glandular/adipose segmentation in breast is important for accurate dose determinations in MC, especially for breast LDR brachytherapy.
Med Phys; 01/2009
