Radyoterapiye Bağlı İkincil Kanser Riskini Azaltmak Amacıyla Karşı Memeyi Alan Dışında Bırakacak Sütyen ve Zırh Tasarımı

Abstract

In this study, a bra to remove the contralateral breast away from the target breast and different shield designs to reduce the contrlateral breast dose were produced. Simulations were made with MCNP6 for barium borate, sepiolite, borax, copper, cerrobend, lead and water which were positioned 10 cm away from the 2 MeV mono-directional (10 cm x 10 cm) photon source. Cerrobend was the best absorbent material, considering cost, accessibility, formability and melting temperature with HVL (2.74 cm) and TVL (7.34 cm) values. Unshielded and 5 mm thick cerrobend shielded simulations were performed on the phantom surface with15 cm x 15 cm, 2 MeV photon beams directed to a 30 cm x 30 cm RW3 solid phantom, and PDD and horizontal dose profiles were compared. In Monte Carlo (MC) simulations, it was found that the shield decreased the dose by 10-15% at 2 and 5 cm depths in the in-field area, while the dose increased by 15% due to the build-up effect on the surface. Secondly a bra and water drop shaped or square-shaped shields were produced. RayStation VMAT plans were made with CT images taken with and without bras on the silicone breasts placed on Alderson Rando Phantom and treatment plans were made delivering 50 Gy in 2 Gy fractions to the left breast and local lymphatics. The mean dose of the contralateral breast was reduced by approximately 20 cGy with the bra. Gafchromic films were placed in the 0, 2, 5 cm depths of the solid water phantom (upper edge of the field, in the the middle of the field and the lower edge of the field) and with 6 MV, 15x15 cm2 photon beams unshielded, 5 mm shielded and 7 mm shielded measurements were made. In solid phantom measurements, 5 mm and 7 mm shields reduced the in-field dose approximately 200-220 cGy, 200 cGy at 2 cm and 5 cm depth, respectively, and the out-of-field dose from 50 cGy to 10 cGy as it moves away from the target field. Then gafchromic films were placed on the medial, nipple, lateral parts of the right and left breasts on Alderson Rando phantom, and measurements were done without the bra and the shield, with only the bra (without shield) and with both bra and 5 mm shield on the right breast. When only bra was used or the bra+shield were used together, the film doses in the medial part of the contralateral breast decreased by on average of 30 cGy (maximum 70 cGy) with the bra and on average 95 cGy with bra+shield; nipple doses decreased by 5 cGy (maximum 10 cGy) with bra and 35 cGy (maximum 55 cGy) with bra+shield; lateral film doses decreased on average of 18 cGy (maximum 25 cGy) with bra and on average of 25 cGy (maximum 30 cGy) with bra+shield. According to Alderson Rando phantom measurements, the out-of-field dose to the contralateral breast decreased by a maximum of 70 cGy only with the bra, and a maximum of 95 cGy when the bra and shield were used together.