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

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

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 (D_av) and organ equivalent dose (OED) of lung, which was partially included within the treatment volume, was found from 3d-conformal radiotherapy plans. The D_av 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.

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 D_av 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.

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