Treatment of large stage I-II lung tumors using stereotactic body radiotherapy (SBRT): Planning considerations and early toxicity

Purpose: To study the dosimetric predictors of early clinical toxicity following SBRT in patients with lung tumors and planning target volumes (PTV) exceeding 80 cm(3). Methods: Eighteen consecutive patients who were treated using volumetric modulated arc therapy (RapidArc(TM)) were assessed. All were either unfit or refused to undergo surgery or chemoradiotherapy. PTV planning objectives were as used in the ROSEL study protocol. Clinical toxicity was scored using Common Toxicity Criteria AE4.0. Lung volumes receiving 5, 10, 15, and 20 Gy (V5, V-10, V15 and V20) and mean lung dose were assessed and correlated to symptomatic radiation pneumonitis (RP). Results: Median age, age-adjusted Charlson-comorbidity score and PTV size were 74, 7.5 and 137 cm(3), respectively. At a median follow-up of 12.8 months, 8 deaths were recorded: 5 arising from comorbidity, 2 were potentially treatment-related and 1 had local recurrence. RP was reported in 5 patients (grade 2 in 3 and grade 3 in 2). All RP occurred in plans without a high priority optimization objective on contralateral lung. Acute RP was best predicted by contralateral lung V-5 (p < 0.0001). Conclusion: After SBRT using RapidArc in lung tumors >80 cm(3), the contralateral lung V-5 best predicts RP. Limiting contralateral lung V-5 to <26% may reduce acute toxicity. (C) 2010 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 97 (2010) 431-436