Radiation therapy for stage IIA and IIB testicular seminoma: peripheral dose calculations and risk assessments

Abstract

This study was conducted to calculate the peripheral dose to critical structures and assess the radiation risks from modern radiotherapy for stage IIA/IIB testicular seminoma. A Monte Carlo code was used for treatment simulation on a computational phantom representing an average adult. The initial treatment phase involved anteroposterior and posteroanaterior modified dog-leg fields exposing para-aortic and ipsilateral iliac lymph nodes followed by a cone-down phase for nodal mass irradiation. Peripheral doses were calculated using different modified dog-leg field dimensions and an extended conventional dog-leg portal. The risk models of the BEIR-VII report and ICRP-103 were combined with dosimetric calculations to estimate the probability of developing stochastic effects. Radiotherapy for stage IIA seminoma with a target dose of 30 Gy resulted in a range of 23.0–603.7 mGy to non-targeted peripheral tissues and organs. The corresponding range for treatment of stage IIB disease to a cumulative dose of 36 Gy was 24.2–633.9 mGy. A dose variation of less than 13% was found by altering the field dimensions. Radiotherapy with the conventional instead of the modern modified dog-leg field increased the peripheral dose up to 8.2 times. The calculated heart doses of 589.0–632.9 mGy may increase the risk for developing cardiovascular diseases whereas the testicular dose of more than 231.9 mGy may lead to a temporary infertility. The probability of birth abnormalities in the offspring of cancer survivors was below 0.13% which is much lower than the spontaneous mutation rate. Abdominoplevic irradiation may increase the lifetime intrinsic risk for the induction of secondary malignancies by 0.6–3.9% depending upon the site of interest, patient’s age and tumor dose. Radiotherapy for stage IIA/IIB seminoma with restricted fields and low doses is associated with an increased morbidity. These data may allow the definition of a risk-adapted follow-up scheme for long-term testicular cancer survivors.