Skin Dosimetry in Breast Teletherapy on an Anthropomorphic and Anthropometric Phantom

This paper addresses the breast Teletherapy Dosimetry. The goal is to evaluate and compare absorbed doses in equivalent skin tissue, TE-skin, of an anthropomorphic and anthropometric breast phantom submitted to breast radiotherapy. The methodology involved the reproduction of a set of tomographic images of the phantom, the elaboration of conformational radiotherapy planning and the synthetic breast irradiation by parallel opposed fields with prescribed dose of 1.80 Gy to the Target Volume (PTV). Radiochromic films EBT2 were selected as dosimeters. Two independent calibration processes of films with solid water Gammex 457 plates and water filled box were produced. Curves of Optical Density (OD) versus absorbed dose were produced. Dosimeters were positioned in the external region of the breast phantom in contact with TE-skin. The irradiation process was prepared in duplicate to check the reproducibility of the technique. The radiochromic films were scanned and their response in RGB (Red, Green, Blue) analyzed by the Image software. The optical density was obtained and converted to absorbed dose based on the calibration curves. Thus, the spatial distribution of the absorbed dose in the skin was reproduced. The absorbed doses measured on the radiochromic films in TE-skin showed doses values in the upper and lower quadrants in the range of 54%, 72% and 68% of prescribed dose. The values are mean 64% of the precribed dose. As conclusion, the depth absorbed dose measured in solid water plates or water box reproduce values with no significant statistical differences for both calibration processes of the radiochromic films. It was observed that the skin received absorbed doses ranging from 50% to 78% of the prescribed dose in the two parallel opposed irradiation fields.