secondary cancer risk after radiotherapy of seminoma stage one

Introduction: in radiation treatment of stage one seminoma (sos) induced secondary cancer in organs at risk (oars), is late toxicity of major concern. this study aimed to compare the secondary cancer risk in radiotherapy of sos in two-dimensional conventional (2d) radiation therapy and three-dimensional conformal radiation therapy (3dcrt). material and methods: ct scan images of 10 patients with sos were used to design 2d conventional and 3d conformal treatment plans using 25 gy in 20 sessions. the life attributable risk (lar) of the liver, stomach, and colon were calculated using the organ equivalent dose (oed) model for organs in the radiation field and the biologic effects of ionizing radiation vii (beir vii) model for organs out of the field. results: lar of oars in radiation fields such as the liver and stomach were obtained 40% higher in the 2d treatment than in the 3d treatment, while as for the colon, it was 17% lower in the 2d treatment than in the 3d treatment. the lar values of kidneys located outside the radiation field in the 2d treatment were calculated at 0.04%. conclusion: increasing the prescribed dose (25 vs. 20) as well as the number of treatment sessions (20 vs. 10) resulted in increase in the lar of the liver, stomach, and colon. therefore, estimating the cancer risk of critical organs exposed to radiation through examining the effects of dose fractionation and prescribed doses can be used in optimizing of the treatment plan for seminoma, selecting a better treatment method by oncologists, and patient follow-up.