A dosimetric parameter to limit chest wall toxicity in SABR of NSCLC

Chest wall (CW) toxicity (rib fracture and/or pain) is a recognized complication of stereotactic ablative radiotherapy (SABR) for non-small-cell lung cancer. The aim of this study was to evaluate the frequency of CW toxicity following SABR and to propose a new dosimetric parameter.

We reviewed the charts and SABR plans from patients treated for T1-T2N0 peripheral non-small-cell lung cancer between 2009 and 2015. The CW structure was created through a 3-cm expansion of the lung. The median dose delivered to the planning target volume was 60 Gy. SABR was delivered in three fractions for patients with CW V₃₀ < 30 cm³. If the CW V₃₀ exceeded 30 cm³, five fractions were used, and the plan was optimized based on CW V₃₇ (biologically equivalent to the V₃₀ of three-fraction plans).

In 6 years, 361 lesions from 356 patients were treated (3 fractions: 297; 5 fractions: 64). The median follow-up was 16 months. 23 patients (6.5%) developed CW toxicity after a median time of 10 months following treatment. The mean CW V₃₀/V₃₇ was 21 cm³ for patients with CW toxicity and 17 cm³ for patients without toxicity (p < 0.05). The 2-year local control and the CW toxicity rates were similar, whether patients received three or five fractions (97% vs 96% and 7% vs 5%).

When the CW V₃₀ is >30 cm³, altered fractionation combined with V₃₇ optimization can limit CW toxicity. Advances in knowledge: The CW V₃₇ is a suggested dosimetric parameter adapted to fractionation that may potentially limit CW toxicity after lung SABR.