Evaluation of calculation algorithms implemented in different commercial planning systems on an anthropomorphic breast phantom using film dosimetry

Purpose: To evaluate the accuracy of dose calculation algorithms of different planning systems for postoperative tangential radiotherapy in breast cancer. Material and Methods: On a CT dataset of an anthropomorphic phantom, a structure set of the left lung, clinical target volume (CTV), planning target volume, heart, and external contour were delineated. The dataset was processed by six radiation oncology centers participating in this multicenter dosimetry project. Conventional plans with two tangential wedged fields were generated in MasterPlan (R), Pinnacle (R), Eclipse (R), TMS (R), and PrecisePLAN (R). Plan calculations were done using the beam data of local linacs. The dose distributions were verified under local conditions with Gafchromic (R)-EBT films. Results: In all planning systems, deviations between calculation and measurement were around +/- 3% in the CTV in the measured plane. Only small areas with deviations of +/- 5% were detected. Pencil-beam (PB) calculations overestimated the dose inside the lung by up to 23%. Collapsed cone (CC) underestimated the lung dose by up to 6%. Conclusion: CC calculates the dose distribution more accurately than PB. Inside regions with electron disequilibrium, however, the dose is slightly underestimated.