Survival Impact of Cardiac Dose Following Lung Stereotactic Body Radiotherapy.

INTRODUCTION: The purpose of this study was to determine the impact of radiation dose to substructures of the heart in lung stereotactic body radiotherapy (SBRT) patients on non-cancer-related deaths.

METHODS: Patients treated with lung SBRT at a single institution from 2005 to 2013 were included. The heart and its substructures were contoured, and dose was calculated including mean, max, and max 10 cc dose. Clinical variables including stage, histology, age, gender, Charlson comorbidity index (CCI), preexisting cardiac disease, pulmonary function (forced expiratory volume in 1 second, diffusion capacity), and smoking status were explored for association with non-cancer-related deaths in univariable (UVA) and multivariable (MVA) analyses. Heart dosimetric parameters were correlated with the risk of radiation pneumonitis (RP) using UVA and MVA.

RESULTS: A total of 189 patients were included with median age of 76 years (range, 48-93 years). Of these patients, 45.5% were female, 27.5% were T2, 16.9% were current smokers, 64% had preexisting cardiac risk factors, and 34.5% had CCI score of ≥ 3. Mean lung dose ± SD was 456 ± 231 cGy. Heart max, mean, and 10 cc doses were 1867 ± 1712 cGy, 265 ± 269 cGy, and 1150 ± 1075 cGy, respectively. There were 14 (7.4%) ≥ Grade 2 RP and 3 (1.6%) were ≥ Grade 3. The median overall survival was 37.3 months (95% confidence interval, 29.8-45.3 months). On UVA, female gender (P < .01), higher Eastern Cooperative Oncology Group (P = .01), cardiac risk (P < .01), CCI (P < .01), and bilateral ventricles max dose (P = .02) were associated with non-cancer-related deaths; on MVA, bilateral ventricles max dose was significant (P = .05). No heart parameters were associated with RP.

CONCLUSIONS: Higher bilateral ventricles max dose is associated with poorer survival. Heart dose parameters should be considered when planning patients for SBRT.