Evaluation of electron dose calculations accuracy of a treatment planning system in radiotherapy of breast cancer with photon-electron technique

Aim: The aim of this study was to assess the accuracy of electron dose calculations of Prowess Panther treatment planning system (TPS) for abutting photon-electron (PE) technique. In this work, we have assessed the accuracy of electron dose calculations in a simulated internal mammary field because this field is irradiated with electron in PE technique. Materials and Methods: In this study, regions of in-field, under electron shield, and outside the internal mammary field were evaluated. Thermoluminescent dosimeter (TLD-700) chips were used within RANDO phantom for dose measurement. Prowess Panther TPS was also applied for dose calculation. Finally, confidence limit values were obtained to quantify the TPS electron dose calculation accuracy of an internal mammary field. Results: The results show that for outside of field and under shield regions, Prowess Panther TPS underestimated the dose compared to the measured doses by TLD-700, whereas for in-field regions, the calculated doses by Prowess Panther TPS compared to the measured doses by TLD-700, for some points are overestimated and other points are underestimated. Finally, the confidence limit values were obtained for various regions of the internal mammary field. Confidence limits for in-field, outside of field, and under shield regions were 54.23, 108.19, and 80.51, respectively. Conclusions: It is concluded that the accuracy of electron dose calculations of Prowess Panther TPS is not adequate for internal mammary field treatment. Therefore, it is recommended that for fields with electron beams Prowess Panther TPS calculations should not be entirely relied upon.