HDR brachytherapy combined with three-dimensional conformal vs. intensity-modulated radiotherapy in left-sided breast cancer patients including internal mammary chain: comparative analysis of dosimetric and technical parameters.

Abstract

The treatment of the internal mammary chain (IMC) with radiation therapy (RT) for patients with breast cancer remains a controversial issue. Different treatment techniques have been proposed, including oblique electrons, electron photon (EP) combination or partially wide tangents (PWT). However, the residual heart dose can remain significant mainly for left-sided lesions. With PWT and Intensity Modulated Radiotherapy (IMRT), respiratory movements and errors in IMC localization remains a problem. The goal of this paper is to evaluate the impact of IMC brachytherapy (BT) combined with three-dimensional conformal radiotherapy planning (3DCRT) on heart, lungs and contralateral breast doses compared with IMRT. All plans including IMCBT plus 3DCRT were done on PLATO whereas IMRT plans were generated using the Cadplan-Helios inverse treatment planning software module with sliding window technique. Dose volume histograms (DVHs) were calculated for all volumes of interest (VOI). The VD95-107% (volume enclosed between the 95% and the 107% isodose surfaces) was used to measure the overall coverage of planning target volume (PTV). Conformity and homogeneity index was also calculated for the PTV. Dose distribution in the surrounding normal tissue was evaluated. Average VD95-107% was found 23.3% and 78.18% with IMCBT plus 3DCRT and IMRT respectively. The mean conformity of the PTV was found to be 1.06 and 1.12 with IMCBT plus 3DCRT and IMRT respectively. The mean homogeneity (HI95/107) was found 1.4 and 3.32 IMCBT plus 3DCRT and IMRT respectively. Using the IMCBT and 3DCRT technique, the mean dose to the heart, contralateral breast, ipsilataral lung and contralateral lung decreased with a value of 32%, 6.76%, 20% and 5.52% respectively compared with IMRT. This novel technique of IMCBT plus 3DCRT has the potential to reduce dose to the heart and lungs and rival IMRT because of its unique advantages in localization, obviating the need for respiratory gating and maximum sparing of heart and other structures.