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Sci—Sat AM(2): Brachy — 02: The Sensitivity of BED and TCP Parameters to Dose Heterogeneity in Brachytherapy Treatments
Author(s) -
Afsharpour H,
Reniers B,
Verhaegen F,
Beaulieu L
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3476214
Subject(s) - brachytherapy , homogeneous , nuclear medicine , monte carlo method , materials science , medicine , radiology , physics , mathematics , radiation therapy , statistics , statistical physics
Purpose: To investigate the sensitivity of radiobiological parameters to dose heterogeneity in brachytherapy. Materials and Methods: Biological effective dose ( BED ) is calculated using a homogeneous and a heterogeneous model. The homogeneous model is based on the minimal peripheral dose to the target and does not take into account the heterogeneity of the dose distribution in brachytherapy. The heterogeneous model is capable of taking the dose heterogeneity into account. Different Monte Carlo calculation protocols were used for five breast permanent seed implant patients. The tumor control probability ( TCP ) was calculated for both the homogeneous and the heterogeneous models. Results: The homogeneous model is overestimating the BED in all calculation cases. This overestimation is higher for plans with higher D 90 values. For example, by about 10% for a plan with D 90 =40 Gy, this overestimation increases to 40% when the D 90 =90 Gy. Depending on the D 90 , the homogeneous model overestimates the TCP vis‐à‐vis the heterogeneous model. In this case the difference is large for intermediate D 90 , however, they agree well for higher D 90 doses. The 50% control dose is higher by 13 Gy while the γ 50 parameter is lower by 60% in the heterogeneous compared to the homogeneous model. Conclusion: The BED is always overestimated by the homogeneous model for all brachytherapy plans. The difference between the homogeneous and the heterogeneous TCP models is large at intermediate D 90 but they agree at higher D 90 . Because of the high dose heterogeneities, the homogeneous model is not suitable for brachytherapy.