(P059) Increased Rates of Radiation Pneumonitis in Patients Receiving Stereotactic Ablative Radiotherapy for Central Versus Peripheral Lung Tumors

Aadel A. Chaudhuri, MD, PhD, Chad Tang, MD, Nicholas Trakul, MD, PhD, Jacob Wynne, BS, Billy W. Loo, MD, PhD, Maximilian Diehn, MD, PhD; Stanford University School of Medicine

Purpose: Treatment of central lung tumors with stereotactic ablative radiotherapy (SABR) has been associated with higher rates of toxicities than in patients with peripheral tumors. Here, we report our institution’s experience in treating central lung tumor patients with SABR, compared with patients treated for peripheral lung tumors.

Methods: We retrospectively reviewed outcomes in 85 patients with a total of 99 primary or metastatic lung tumors treated by SABR. The cohort included 49 central and 50 peripheral tumors, and all were treated with 50 Gy in 4–5 fractions. Outcomes and radiation-associated toxicities were compared between the two groups, not including patients in whom central and peripheral tumors were concurrently treated (eight such patients). Dosimetric analysis was performed on patients with central tumors to determine maximum point dose (MPD) and volumetric maximum dose (Vmax) to central structures.

Results: Median follow-up time was 15 months (range: 1–59 mo). Actuarial local control rate was 84% and 91% (P = .15) at 1 year for central and peripheral lesions, respectively. Median overall survival was 34 and 40 months (P = .55) for patients with central and peripheral tumors, respectively. We observed no hemoptysis and no grade 5 toxicities. Rates of symptomatic toxicity were higher in patients with central tumors (grade 2+, 38% vs 11%; P = .004) but were similar for severe toxicity (grade 3+, 7.7% vs 5.3%; P = .66). The majority of toxicities was due to radiation pneumonitis, the incidence of which was significantly greater in patients with central tumors (grade 2+, 28% vs 2.6%; P = .001; grade 3+, 7.7% vs 0%; P = .08). Dosimetric analysis of 37 central tumor treatment plans revealed that 25 (68%) exceeded at least one of the dose constraints used in Radiation Therapy Oncology Group (RTOG) 0813, most commonly for central airway and/or great vessels. Toxicity rates were similar in patients exceeding RTOG 0813 constraints compared with those meeting them (grade 2+, 32% vs 33%; P = .86).

Conclusion: Central lung tumor patients treated with SABR appear to have greater risk for radiation pneumonitis than patients with peripheral tumors. A subset of commonly used dosimetric constraints for lung SABR, particularly those for central airway and great vessels, may be more conservative than necessary.