The relationship of body mass index to setup errors, dosimetric parameters and incidence of radiation pneumonitis in non-small cell lung cancer patients undergoing intensity-modulated radiation therapy: a single-center observational study.

Background: The relationship among body mass index (BMI), setup error and radiation pneumonitis is not clearly illustrated.

Objective: The present study aimed to investigate the role of BMI in non-small cell lung cancer (NSCLC) patients' radiation treatment, focusing on its relationship with setup error of patient positioning, the dosimetric parameters of intensity-modulated radiation therapy (IMRT) and the incidence of radiation pneumonitis.

Methods: This prospective observational study included 523 cases of NSCLC patients during 2020-2022. Patients were divided into different groups by different BMI. The setup error was obtained by cone beam CT (CBCT) at three positions, lateral (LAT), longitudinal (LNG) and vertical (VRT). IMRT dosimetric parameters of V₅, V₂₀, and mean dose were collected.

Results: Patients with BMI ≥28 kg/m² showed significantly higher absolute values of LAT, LNG and VRT, higher V₅, V₂₀, mean dose, as well as higher total incidence of radiation pneumonitis and grade III radiation pneumonitis compared with patients with BMI <24 kg/m² or 24-28 kg/m². Spearman's analysis demonstrated that the absolute values of LAT, LNG and VRT were positively correlated with BMI, and positive correlation existed among BMI, dosimetric parameters and setup errors. ROC curves showed that LAT in setup errors and V₅ in dosimetric parameters had the best diagnostic value for prediction of radiation pneumonitis. Only BMI, LAT, V₅ and V₂₀ were the independent risk factors for radiation pneumonitis.

Conclusions: Setup error caused by higher BMI might be associated with the dosimetric parameters, as well as the incidence of radiation pneumonitis in NSCLC patients.