Room: Exhibit Hall | Forum 7
Purpose: A challenge facing the physics community has been plan quality checks for high-dose-rate (HDR) brachytherapy treatment planning. This study aims to develop a QA method of manually verifying the planned treatment time from treatment planning system (TPS) for HDR breast brachytherapy using multi-lumen balloon applicators.
Methods: Treatment plans for 74 breast cancer patients that underwent HDR breast brachytherapy were separated into three groups and reviewed in their respective TPS: 32 SAVI patients in OncentraBrachy, 37 SAVI patients and 5 Contura patients in BrachyVision. A number of parameters such as source air kerma strength (ASK), total treatment time, prescription dose (Rx), volume covered by the 100% isodose line (V100) were recorded. These parameters were used to fit the data from three groups respectively using the formula PredictedTxTime = Rx Ã—K Ã— V100â?½Â²/Â³â?¾/ASK derived in Das et alâ€™s study (Brachytherapy 2006 Vol 5). After obtaining fitted K values, the treatment times from TPS were compared with the predicted times from the formula.
Results: The constant K from fitting parameters varied among three groups: Oncentra-SAVI K=909, BrachyVision-SAVI K=991 and Brachyvision-Contura K=1222. The variation of K values suggests each clinical should fit their own data to obtain institute specific K values. Direct comparison of treatment times obtained through TPS and those calculated from the formula showed a mean difference of 0.0Â±2.1% for Oncentra-SAVI, 0.0Â±4.4% for BrachyVision-SAVI, and 2.3Â±1.0% for BrachyVision-Contura with maximum difference 5.4%, 16.5% and 3.5% respectively. Further investigating the outlier case with 16.5% difference identified a sub-optimal clinical plan with skin dose exceeding the tolerance.
Conclusion: The close agreement between the expected treatment times supports the validity and reliability of the proposed QA method. Utilizing this manual treatment time calculation method will provide an efficient way for checking both TPS system and HDR breast treatment plan quality.