1018 - Phase 1 Trial of CT-Guided Stereotactic Adaptive Radiotherapy (CT-STAR) for Treatment of Ultra-Central Early-Stage Non-Small Cell Lung Cancer (NSCLC)

05:20pm - 05:25pm ET

Room 258

Presenter(s)

Alden D'Souza, MD, MPHS - Washington University in St. Louis School of Medicine, St Louis, MO

A. D'Souza¹, J. P. Schiff², D. Hong¹, R. Mueller¹, F. Forghani¹, T. R. Mazur¹, M. R. Waters¹, A. K. Bhatt¹, R. Beckert¹, G. R. Vlacich¹, E. Laugeman¹, C. G. Robinson¹, and P. Samson¹; ¹WashU Medicine, Department of Radiation Oncology, St. Louis, MO, ²Department of Radiation Oncology, Keck School of Medicine, University of Southern California, Los Angeles, CA

Purpose/Objective(s):

Stereotactic body radiotherapy (SBRT) has become a standard of care treatment option for medically inoperable early-stage NSCLC. However, ablative dose to central and ultra central lung tumors remains challenging because of the risk of toxicity to adjacent organs at risk (aOARs). We performed the first prospective cone beam computed tomography (CBCT)-guided adaptive Phase 1 trial to evaluate the safety of 5 fraction SBRT to central and ultra-central NSCLC leveraging a CBCT-guided adaptive system.

Materials/Methods:

A phase 1 trial was designed to evaluate treatment related adverse events and survival outcomes on early stage (I-IIA) NSCLC or mediastinal recurrent NSCLC that are central (within 1 cm) or ultra-central (abutting) the trachea, carina, bronchi, esophagus or great vessels treated with SBRT using a CBCT-guided adaptive system. Each daily adapted plan and scheduled plan was evaluated with a strict isotoxic approach for both the planning target volume and the aOARS. The adaptive plan was selected for treatment if there was a 5% improvement in GTV or PTV coverage and all dose constraints were maintained. All patients were planned for 55 Gy/5 fractions. The primary endpoint was the rate of possible, probable or definite CTCAE V5.0 grade 3 or greater adverse events (G3+) 12 months post completion of CT-STAR. Our exploratory endpoints will include local control, overall control and OAR dose.

Results:

Seventeen patients were consented and treated. Mean age was 69.7 (SD: 5.7). Six (35%) patients had ultra-central lesions and eleven (65%) had central lesions. Fourteen patients had stage I NSCLC, two had stage II NSCLC and one had a local recurrence of a resected stage II NSCLC. There have been no local failures, with a median follow-up of 13.4 months (IQR 9.2-21.1). There were two possible G3+ adverse events, including acute G4 hypoxia and a late G4 respiratory failure in separate patients. Of the 85 fractions, 59 (69%) were adapted. The mean total time of treatment delivery was 69 minutes (SD: 15), with approximately 21 minutes (SD: 7) of that being part of the adaptive process.

Conclusion:

Utilizing CT-STAR, the treatment of central and ultra-central early-stage NSCLC is consistently achievable with acute and long-term adverse event rates lower than historical norms and durable local control at one year. Larger studies with long-term follow-up are needed to confirm durability of our reported outcomes.