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On the Importance of Heterogeneous Calculation in Brachytherapy: A Radiobiological Point of View

H Afsharpour

H Afsharpour1*, F Verhaegen2, L Beaulieu3, (1) Centre Hospitalier Univ de Quebec, Quebec, QC (2) Maastro clinic, Maastricht

TH-C-213AB-12 Thursday 10:30:00 AM - 12:30:00 PM Room: 213AB

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.

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