Radiotherapy for non-malignant shoulder syndrome: Is there a risk for radiation-induced carcinogenesis?

PURPOSE: To estimate the organ-specific probability for carcinogenesis following radiotherapy for non-malignant shoulder syndrome.

METHODS: Photon-beam radiation therapy to 6 Gy for shoulder syndrome was simulated with a Monte Carlo code. An androgynous computational phantom representing a typical adult was used to calculate the radiation dose to out-of-field organs having a predilection for carcinogenesis. The organ-specific lifetime attributable risk (LAR) for out-of-field cancer induction was estimated by the organ dose calculations and the proper risk factors introduced by the BEIR-VII report. The average dose (Dav ) and organ equivalent dose (OED) of lung, which was partially included within the treatment volume, was found from 3d-conformal radiotherapy plans. The Dav and OED were used to estimate the lung cancer risk with a linear and mechanistic models, respectively. All risk assessments were made for 50- and 60-year-old male and female patients.

RESULTS: Monte Carlo simulations resulted in an out-of-field organ dose range of 0.7-48.4 mGy. The LARs for out-of-field cancer induction were (1.4 × 10-4 )% to (2.8 × 10-2 )%. These probabilities were at least 403 times lower than the respective lifetime intrinsic risk (LIR) values. The Dav and OED of lung was up to 164.9 and 142.3 mGy, respectively. The LAR for developing lung malignancies varied from 0.11 to 0.18% by the model used and the patient's age and gender. The lung cancer risks were 36-64 times smaller than the LIRs.

CONCLUSIONS: The estimated probabilities for developing malignancies due to radiotherapy for non-malignant shoulder syndrome are minor relative to the natural cancer occurrence rates.