Miami Cancer Institute Miami, Florida, United States
M. D. Chuong1, K. E. Mittauer2, M. F. Bassetti3, C. Glide-Hurst3, C. Rojas2, N. S. Kalman2, M. C. Tom4, M. Rubens5, J. Crosby3, A. Burr3, A. Gutierrez2, N. Bassiri-Gharb2, M. P. Mehta6, and R. Kotecha7; 1Miami Cancer Institute, Miami, FL, 2Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, FL, 3Department of Human Oncology, University of Wisconsin Hospitals and Clinics, Madison, WI, 4Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 5Department of Biostatistics, Miami Cancer Institute, Baptist Health South Florida, Miami, FL, 6Miami Cancer Institute, Baptist Health South Florida, Miami, FL, 7Baptist Health South Florida, Miami, FL
Purpose/Objective(s): Single-fraction (1-fx) SABR improves patient and provider convenience, facilitates treatment of multiple lesions, and reduces healthcare costs. Adoption has been limited largely due to suboptimal soft tissue contrast quality of x-ray-based imaging on standard linacs and concerns of intra-fraction geographic miss. MR-linacs (MRLs) provide excellent soft tissue visualization using MR imaging prior to and continuously during treatment. Prospective outcomes of 1-fx MR-guided SABR have not been reported. Materials/
Methods: We conducted a multi-center phase 2 trial of 1-fx SABR delivered on a 0.35T MRL for primary or metastatic lesions of the lung (30-34 Gy; BED10 = 120-149.6 Gy), liver (35-40 Gy; BED10 = 157.5-200 Gy), pancreas (25 Gy; BED10 = 87.5 Gy), adrenal gland (25 Gy), kidney (25 Gy), and abdomen/pelvis (A/P) lymph nodes (LNs) (25 Gy). Online adaptive RT (oART) was used as needed to meet OAR constraints. Continuous intrafraction, bi-planar soft tissue tracking of the target lesion coupled with automatic beam gating were mandatory; breath hold was preferred for treatment efficiency. Primary objectives included feasibility (total in-room time [TIRT] <90 min for >80% of patients) and safety (acute grade >3 toxicity <15%, no grade 5 toxicity as per CTCAE v5.0). Secondary objectives included 1-yr local control (LC), 1-yr overall survival (OS), quality of life (QOL) as per FACT-G, and late grade >3 toxicity. Results: The study accrued the planned 30 patients (32 lesions) at 2 U.S. institutions between June 2021 and June 2023. All had 1 lesion except for 2 patients with 2 lesions each. Targets were in the lung (n=11; 34.4%), adrenal gland (n=9; 28.1%), A/P LNs (n=6; 18.8%), liver (n=5; 15.6%), and pancreas (n=1; 3.1%). Median GTV and PTV volumes were 3.7 cc (range, 1.0-40.5 cc) and 15.8 cc (range, 5.0-95.8 cc), respectively. oART was used for 53.1% (17/32) of treated lesions, 15 (88.2%) of which were in the A/P. Median TIRT and treatment times were 53 min (range, 39-195 min) and 30 min (range, 15-144 min), respectively. TIRT was <60 min and <90 min for 21 patients (70%) and 25 patients (83.3%), respectively. TIRT was >90 min for 4 patients (median 116 min; range, 96-195 min). Median follow-up was 12 months (range, 1-14 months) from SABR. Acute grade 3 adverse events occurred in 3 patients (10%); 2 were not treatment-related after adrenal SABR (pneumonia, acute respiratory failure), 1 was possibly treatment-related after lung SABR (pericardial effusion that spontaneously resolved). No acute grade 4-5 or late grade >3 toxicity occurred. 1-yr LC and OS were 100% and 78.5%, respectively. Total FACT-G scores remained stable at 3 and 12 months after SABR. Conclusion: This is the first prospective trial of 1-fx MR-guided SABR that enrolled patients predominantly with mobile A/P tumors. The primary feasibility and safety objectives were met. No local failure occurred during the study period. Larger prospective studies are warranted as 1-fx SABR may be especially advantageous for treating multiple metastases.
