To identify the dose-volume parameters that predict the risk of chest wall (CW) pain and/or rib fracture after lung stereotactic body radiotherapy.

From a combined, larger multi-institution experience, 60 consecutive patients treated with three to five fractions of stereotactic body radiotherapy for primary or metastatic peripheral lung lesions were reviewed. CW pain was assessed using the Common Toxicity Criteria for pain. Peripheral lung lesions were defined as those located within 2.5 cm of the CW. A minimal point dose of 20 Gy to the CW was required. The CW volume receiving >or=20, >or=30, >or=40, >or=50, and >or=60 Gy was determined and related to the risk of CW toxicity.

Of the 60 patients, 17 experienced Grade 3 CW pain and five rib fractures. The median interval to the onset of severe pain and/or fracture was 7.1 months. The risk of CW toxicity was fitted to the median effective concentration dose-response model. The CW volume receiving 30 Gy best predicted the risk of severe CW pain and/or rib fracture (R(2) = 0.9552). A volume threshold of 30 cm(3) was observed before severe pain and/or rib fracture was reported. A 30% risk of developing severe CW toxicity correlated with a CW volume of 35 cm(3) receiving 30 Gy.

The development of CW toxicity is clinically relevant, and the CW should be considered an organ at risk in treatment planning. The CW volume receiving 30 Gy in three to five fractions should be limited to <30 cm(3), if possible, to reduce the risk of toxicity without compromising tumor coverage.