Predicting the risk of secondary lung malignancies associated with whole-breast radiation therapy.

Purpose: The risk of secondary lung malignancy (SLM) is a significant concern for women treated with whole-breast radiation therapy after breast-conserving surgery for early-stage breast cancer. In this study, a biologically based secondary malignancy model was used to quantify the risk of secondary lung malignancies (SLMs) associated with several common methods of delivering whole-breast radiation therapy (RT).

Methods And Materials: Both supine and prone computed tomography simulations of 15 women with early breast cancer were used to generate standard fractionated and hypofractionated whole-breast RT treatment plans for each patient. Dose-volume histograms (DVHs) of the ipsilateral breast and lung were calculated for each patient on each plan. A model of spontaneous and radiation-induced carcinogenesis was used to determine the relative risks of SLMs for the different treatment techniques.

Results: A higher risk of SLMs was predicted for supine breast irradiation when compared with prone breast irradiation for both the standard fractionation and hypofractionation schedules (relative risk [RR] = 2.59, 95% confidence interval (CI) = 2.30-2.88, and RR = 2.68, 95% CI = 2.39-2.98, respectively). No difference in risk of SLMs was noted between standard fractionation and hypofractionation schedules in either the supine position (RR = 1.05, 95% CI = 0.97-1.14) or the prone position (RR = 1.01, 95% CI = 0.88-1.15).

Conclusions: Compared with supine whole-breast irradiation, prone breast irradiation is associated with a significantly lower predicted risk of secondary lung malignancy. In this modeling study, fractionation schedule did not have an impact on the risk of SLMs in women treated with whole-breast RT for early breast cancer.