Silicone prostheses are implanted inside the human body for medical aesthetics and reconstructive reasons. The presence of a silicone prosthesis around the radiotherapy volume may alter radiotherapy dose distribution and cause overdose and underdose areas in the target volumes and organs at risk. The interaction of silicone with radiation may be two-sided since high dose radiation may cause alteration of the physical and chemical prop-erties of silicone which further contributes to changes in the dose distribution. The aim of this study was to evaluate the changes in radiation dose distribution caused by silicone and the effects of irradiation on silicone elastomer prostheses. A special set-up was prepared in the water phantom to obtain depth dose and profile data for non-irradiated silicone blocks prior to the irradiation schedule. Entrance and exit doses between silicone and water medium were measured using thermoluminescence dosimetry (TLD). Hardness tests on silicone blocks were performed by using Tronic Shore A Durometer device and density tests were performed by using Scaltec density determination instrument. Irradiation of the silicone was performed using a linear accelerator with 6 MV and 10 MV photon energies, 2 Gy daily fractions in 5 weeks were delivered to a total dose of 50 Gy. After the completion of 5 weeks schedule depth doses, profile measurements, entrance-exit doses and density-hardness tests were repeated. The non-irradiated silicone blocks affected the depth dose distribution in the water phantom to a maximum dose reduction of 1.5% for 6 MV and 1.6% for 10 MV. After the 5 weeks of irradiation, depth dose reduction increased to 2.5% for 6 MV and 2.0% for 10 MV. Silicone blocks affected the dose profile as well: maximum dose difference was 2.7% for 6 MV and 2.4% for 10 MV for non-irradiated silicone, 2.6% for 6 MV, and 2% for 10 MV after 50 Gy. However, these changes in depth dose and profile data in non-irradiated and irradiated silicone were not significant. There was up to an 8% dose decrease in exit doses beyond the silicone with the use of a single direct irradiation field, which is expected to be reduced with multi-field radiotherapy. The physical properties of the non-irradiated and irradiated silicone measured by hardness and density tests were similar. The only physical difference we noted was the discoloration of silicone to a yellowish color. According to our results silicone elastomer prostheses did not have significant effects on dose distribution after 50 Gy irradiation, and radiation doses used for radiotherapy did not alter the physical properties of silicone blocks except for discoloration.
