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.
Highlights
Early-stage breast cancer patients can benefit from post lumpectomy radiation therapy
For an α/β = 2 Gy, the EQD2 value of the hypofractionation scheme is 49.6 Gy, this value being the closest to the 50 Gy value, corresponding to the conventional fractionation scheme. Based on this information and according to the results presented, it can be concluded that the hypofractionation course to 42.56 Gy in 16 fractions is a good candidate for the treatment of breast cancer, as this tumor has low α/β ratio values in relation to other types of tumors, where the typical value is around 10 Gy
Starting by analyzing the results presented in table 3, it is possible to observe that for all original treatment plans with a conventional fractionation regime, all dosimetric parameters evaluated meet the tolerance criteria of the respective organs at risk
Summary
Early-stage breast cancer patients can benefit from post lumpectomy radiation therapy. Breast cancer standard management recommends treatment with photon external beam radiotherapy by irradiating the entire breast with a total dose of 50 Gy in fractional doses of 2 Gy, during five working weekdays (conventional fractionation). The linear quadratic model is of paramount importance in radiotherapy and radiobiology, as it provides a simple relation between cell survival and delivered dose, for which it is abundantly used to predict in vivo and in vitro biological responses to ionizing radiation.
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