(S038) Pulmonary Dose-Volume Predictors of Radiation Pneumonitis Following Stereotactic Body Radiation Therapy

Eileen M. Harder, BS, Henry S. Park, MD, MPH, Zhe Chen, PhD, FAAPM, Roy H. Decker, MD, PhD; Department of Therapeutic Radiology, Yale University School of Medicine

PURPOSE: Radiation pneumonitis (RP) can be a significant risk after stereotactic body radiation therapy (SBRT). The purpose of this study was to identify clinical and dosimetric predictors of symptomatic (grade ≥ 2) RP following pulmonary SBRT.

MATERIALS AND METHODS: Patients with ≥ 3 months of follow-up who received SBRT for primary lung cancer were selected from an institutional database. RP was determined retrospectively from all available records, including those from appointments with radiation oncology, pulmonology, and medical oncology and hospitalizations. RP was scored per Common Terminology Criteria for Adverse Events version 4.0 (CTCAE v4.0). Normal lung volume was defined as total lung volume minus gross tumor volume (GTV) on the planning computed tomography (CT). Pulmonary D_max (maximum point dose), mean lung dose (MLD), and Vx (volume of lung receiving ≥ x Gy) in 5-Gy increments were collected. Univariate analyses were performed with the chi-square or Student’s t-test. Dosimetric predictors of RP were identified using multivariate logistic regression with a manual forward stepwise selection technique.

RESULTS: A total of 264 patients were included (median follow-up 29.4 mo). Median prescription dose was 54 Gy (range: 40–60 Gy). Patient characteristics were as follows: 27 (10.2%) had multifocal disease, 58 (22.0%) had T-stage ≥ 2, 26 (9.8%) had prior lung radiotherapy (4.2% with SBRT), and 72 (27.3%) had prior lung resection. Grade ≥ 2 RP occurred in 61 patients (23.1%) with a median onset time of 1.8 months (range: 0.1–16.2 mo). Grade ≥ 3 RP occurred in 23 patients (8.7%). Lung V5, V10, V15, V20, V25, V30, V35, V40, V45, and MLD were significantly associated with grade ≥ 2 RP on univariate analysis (P < .05), but no correlation was seen with lung V50, lung D_max, age, gender, Eastern Cooperative Oncology Group (ECOG) performance status, cigarette use, T stage, location (central/peripheral), lobe (upper/lower) synchronicity, prescribed BED, GTV, ITV, PTV, pretreatment pulmonary comorbidity, or any heart dosimetric volume. Among these significant factors, lung V10 was the strongest predictor of RP on multivariate analysis (P = .006). The median lung V10 was 10.9 Gy. Symptomatic RP was present in 18.9% of patients receiving lung V10 < 10.9 Gy, compared with 27.3% with lung V10 ≥ 10.9 Gy.

CONCLUSIONS: Symptomatic RP occurred in 23.1% of our patients treated with SBRT. Lung V10 was the strongest predictor of grade ≥ 2 RP on multivariate logistic regression, associated with a 30% decrease in risk for patients with V10 < 10.9 Gy compared with ≥ 10.9 Gy. Further research is needed to validate these findings and the importance of lung V10 in predicting symptomatic RP following SBRT.

Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org