Analysis of the impact of chest wall constraints on eligibility for a randomized trial of stereotactic body radiotherapy of peripheral stage I non-small cell lung cancer.

ABSTRACT

INTRODUCTION: Chest wall toxicities are recognized complications of stereotactic radiotherapy (SBRT) in non-small cell lung cancer. To minimize toxicity, the Trans-Tasman Radiation Oncology Group (TROG) 09.02 'CHISEL' study protocol excluded patients with tumours within 1 cm of the chest wall. The purpose of this study is to evaluate the implication of chest wall proximity constraints on patient eligibility, toxicity and potential accrual. METHODS: Exclusion zones of 1 cm beyond the mediastinum and 2 cm beyond the bifurcation of the lobar bronchi were incorporated into the CHISEL credentialing CT dataset. Volumes of lung within which tumours varying from 1 cm to 5 cm in diameter may occupy and remain eligible for the CHISEL study were calculated. These volumes were compared to a hypothetical model in which the 1 cm chest wall proximity restriction was removed. RESULTS: The percentage of lung area in which a tumour mass can occupy and be suitable for CHISEL in the left and right lung were 54% and 60% respectively. Removing the constraint increased the percentage of available lung to 83% and 87% respectively. Considering a 2 cm spherical tumour, only 21% and 31% of tumours in the left and right lung would be eligible with the chest wall constraint, whilst 39% and 50% respectively would be eligible without the constraint. CONCLUSIONS: The exclusion of tumours less than 1 cm to chest wall significantly reduces the proportion of patients eligible for the CHISEL protocol. A review of the literature pertaining to chest wall toxicity after stereotactic radiotherapy supports a change in chest wall exclusion criteria for the CHISEL study.