Stereotactic Radiation for Ultra-Central Non-Small Cell Lung Cancer: A Safety and Efficacy Trial (SUNSET)

INTRODUCTION

The use of stereotactic body radiotherapy (SBRT) for tumors in close proximity to the central mediastinal structures has been associated with a high risk of toxicity. This study (BLINDED FOR REVIEW) aimed to determine the maximally tolerated dose (MTD) of SBRT for ultra-central (UC) non-small cell lung carcinoma (NSCLC), using a time-to-event continual reassessment methodology (TITE-CRM).

METHODS

Patients with T1-3N0M0 (≤ 6 cm) NSCLC were eligible. The MTD was defined as the dose of radiotherapy associated with a ≤ 30% rate of grade (G) 3-5 pre-specified treatment-related toxicity occurring within 2 years of treatment. The starting dose level was 60 Gy in 8 daily fractions. The dose-maximum hotspot was limited to 120% and within the planning tumor volume (PTV); tumors with endobronchial invasion were excluded. This primary analysis occurred two years after completion of accrual.

RESULTS

Between March 2018 and April 2021, 30 patients were enrolled at 5 institutions. The median age was 73 years (range: 65-87) and 17 (57%) were female. PTV was abutting proximal bronchial tree in 19 (63%), esophagus 5 (17%), pulmonary vein 1 (3.3%) and pulmonary artery 14 (47%). All patients received 60 Gy in 8 fractions. The median follow-up was 37 months (range: 8.9-51). Two patients (6.7%) experienced G3-5 adverse events related to treatment: 1 patient with G3 dyspnea and 1 G5 pneumonia; the latter had CT findings consistent with a background of interstitial lung disease. Three-year overall survival was 72.5% (95% confidence interval [CI]: 52.3-85.3%), progression-free survival 66.1% (95% CI: 46.1-80.2%), local control 89.6% (95% CI: 71.2-96.5%), regional control 96.4% (95% CI: 77.2-99.5%) and distant control 85.9% (95% CI: 66.7-94.5%). Quality of life scores declined numerically over time, but the decreases were not clinically or statistically significant.

CONCLUSIONS

60 Gy in 8 fractions, planned and delivered with only a moderate hotspot, has a favorable adverse event rate within the pre-specified acceptability criteria, and results in excellent control for UC tumors.

Stereotactic Radiotherapy for Ultra-Central Lung Oligometastases in Non-Small-Cell Lung Cancer

Background: Stereotactic body radiotherapy (SBRT) in ultra-central (UC) lung tumors, defined in the presence of planning target volume (PTV) overlap or direct tumor abutment to the central bronchial tree or esophagus, may be correlated to a higher incidence of severe adverse events. Outcome and toxicity in oligometastatic (≤3 metastases) non-small-cell lung cancer (NSCLC) patients receiving SBRT for UC tumors were evaluated. Methods: Oligometastatic NSCLC patients treated with SBRT for UC were retrospectively reviewed. Local control (LC), distant metastasis-free survival (DMFS), progression-free survival (PFS) and overall survival (OS) were calculated. Incidence and grade of toxicity were evaluated. Statistical analysis was performed to assess the impact of clinical and treatment-related variables on outcome and toxicity occurrence. Results: Seventy-two patients were treated to a median biologically effective dose (BED) of 105 (75–132) Gy¹⁰. Two-year LC, DMFS, PFS, and OS were 83%, 46%, 43%, and 49%. BED>75 Gy¹⁰ was correlated to superior LC (p = 0.02), PFS (p = 0.036), and OS (p < 0.001). Grade ≥3 toxicity rate was 7%, including one fatal esophagitis. No variables were correlated to DMFS or to occurrence of overall and grade ≥3 toxicity. Conclusions: SBRT using dose-intensive schedules improves outcome in NSCLC patients. Overall toxicity is acceptable, although rare but potentially fatal toxicities may occur.

Safety of stereotactic ablative body radiation for ultracentral stage I non-small cell lung cancer

Recent data suggests that "ultra-central" tumors, generally defined as those abutting the proximal airways, are at particularly high risk for severe complications when treated with stereotactic ablative body radiation (SABR). However, this association has not been consistently demonstrated across reports, possibly due to small numbers, varying definitions of "ultra-central", and the lack of prospective data. New evidence suggests that exposure to VEGF-inhibiting agents may potentiate SABR toxicity and may partially explain the disproportionately high incidence of fatal complications in some reports. Efforts are underway to identify dose-volume limits that can predict complications involving central structures such as the proximal airways, heart, esophagus, and great vessels. The optimal dose for ultra-central SABR has not been determined, though there is a trend towards using more highly fractionated regimens. Further research into the safety of SABR for ultra-central tumors is needed, given the lack of other effective local therapy options for this clinical scenario.