3002 - Lessons Learned from a Direct-to-Unit Single Fraction Lung SBRT Pilot Trial

12:30pm - 01:45pm ET

Poster Hall - Exhibit Hall A

Screen: 2

POSTER

Presenter(s)

Farnoush Forghani, PhD - Washington University in St. Louis, St. Louis, MO

F. Forghani¹, T. R. Mazur¹, J. P. Schiff², D. Hong¹, A. D'Souza³, R. Mueller¹, J. Hamilton⁴, J. Harris⁴, T. Jamruk⁴, J. Hilliard⁵, R. Beckert¹, A. K. Bhatt⁶, G. R. Vlacich¹, C. G. Robinson¹, P. Samson¹, and E. Laugeman¹; ¹WashU Medicine, Department of Radiation Oncology, St. Louis, MO, ²Tulane University School of Medicine, New Orleans, LA, ³Washington University School of Medicine in St. Louis, St. Louis, MO, ⁴Wash U Medicine, St. Louis, MO, ⁵Washington University in St. Louis, St. Louis, MO, ⁶Karmanos Cancer Institute at McLaren Greater Lansing, Lansing, MI

Lessons Learned from a Direct-to-Unit Single Fraction Lung SBRT Pilot Trial

Purpose/Objective(s): Direct-to-unit (DTU) workflows allow for stereotactic body radiation therapy (SBRT) by eliminating conventional CT simulation. We report key technical and workflow lessons learned from a prospective pilot trial of CBCT-guided adaptive DTU single-fraction lung SBRT.

Materials/Methods: Patients with early-stage non–small cell lung cancer or lung oligometastatic disease were enrolled in the prospective ONE-STOP pilot trial of DTU single-fraction (30–34 Gy) SBRT. Offline plans were generated from diagnostic CT before consultation, without simulation CT. On treatment day, online adaptive plans were created using advanced CBCT on a CBCT-based adaptive system. Pre-treatment 4DCT verified tumor motion range and enabled safe free-breathing DTU delivery; 4DCT-based plans were available for comparison and backup if conversion to conventional SBRT was required. Feasibility was defined as successful DTU treatment in ≥70% of patients.

Results: Eight of ten patients were successfully treated using the DTU workflow, meeting protocol-defined OAR and target coverage criteria. Two cases were converted to standard SBRT: one for excessive respiratory motion and one for atypical anatomy and setup variation from diagnostic imaging. Table 1 summarizes lessons learned from the trial, including cases converted to standard SBRT and cases that were successfully treated with ONE-STOP.

Conclusion: CBCT-guided DTU single-fraction lung SBRT is technically feasible but requires prudent patient selection in compliance with treatment conditions, careful tumor motion characterization, and robust adaptive planning to ensure safe implementation.

Table 1: Lessons learned & improved DTU guidelines.

DTU Criterion	Lessons from Trial	Improved Guidelines
Patient Selection	Difficulty for patients maintaining treatment position	• Restrict DTU to patients tolerating stable treatment position & similar setup to the diagnostic CT
Diagnostic CT Suitability	Scan incompatible with adaptive TPS format	• Require high-quality CT (or PET/CT) compatible with adaptive interface • Load offline plan on adaptive treatment delivery system before treatment day
Target Motion Characteristics	Complex target motion	• PTV margins based on expected motion by location (Upper vs. Lower lobe) • If available use PET signal blurring to estimate motion.
Treatment Setup	Scan initiation at treatment isocenter was difficult without initial setup marks	• Standardize mark-free setup protocols with predefined anatomical landmarks (e.g. xiphoid process).
Planning Strategies	Atypical anatomy caused unacceptable adaptive plan	• Use robust planning strategies & beam geometries accommodating change in arm position and anatomical shifts