Evaluation of Fractionation Schemes in Breast Cancer Radiotherapy and Dosimetric Study of the Main Organs at Risk

Abstract

The purpose of this work was to evaluate the impact of different breast cancer radiotherapy regimens on the acceptance of the tolerance criteria of the main organs at risk, the heart, and the ipsilateral lung.In this context, the dosimetric treatment plans of 20 breast cancer patients treated at the Radiotherapy Service of Braga Hospital were analyzed. The treatment planning system was the XiO (Elekta) and the dosimetric treatment plans were performed using with 3D-CRT technique (three-dimensional conformal radiation therapy) and the pencil beam algorithm for photon dose calculation.Two approaches to estimate the equivalence of different radiotherapy schedules have been proposed, the equivalent dose at 2Gy per fraction model and the biologically effective dose model. These models showed that the conventional radiotherapy course to 50Gy in 25 daily fractions is clinically equivalent to the hypofractionation course to 42,56Gy in 16 daily fractions.Obtained results showed that the tolerance criteria for the organs at risk, the heart and the ipsilateral lung, referring to the hypofractionation course to 42,56Gy in 16 daily fractions, are more restrictive than the tolerance criteria of conventional regimen. This means that if the same setup and the same dose coverage in the planning target-volume are used, the tolerance criteria for the organs at risk of hypofractionation regiment are more difficult to attain.These results can assist radiation oncologists in the evaluation of radiotherapy prescription doses for breast cancer, in compliance with the principles of radiation protection.