ESTRO 2024 - Abstract Book

S1961

Clinical - Mixed sites, palliation

ESTRO 2024

Michael D Chuong 1 , Kathryn E Mittauer 1 , Michael Bassetti 2 , Carri K Glide-Hurst 3 , Carolina Rojas 1 , Noah Kalman 1 , Martin Tom 4 , Muni Rubens 5 , Diane Alvarez 1 , Jennie Crosby 3 , James McCulloch 6 , Adam Burr 2 , Alonso N Gutierrez 1 , Nema Bassiri-Gharb 1 , Minesh P Mehta 1 , Rupesh Kotecha 1 1 Miami Cancer Institute, Radiation Oncology, Miami, USA. 2 University of Wisconsin, Radiation Oncology, Madison, USA. 3 University of Wisconson, Radiation Oncology, Madison, USA. 4 MD Anderson Cancer Center, Radiation Oncology, Houston, USA. 5 Miami Cancer Institute, Office of Clinical Research, Miami, USA. 6 Colorado Associates in Medical Physics, Radiation Oncology, Colorado Springs, USA

Purpose/Objective:

Single-fraction SABR has several potential advantages, including improved patient and provider convenience especially when multiple lesions need treatment, reduced healthcare costs, and potential synergy with immunotherapy. However, widespread implementation of single-fraction SABR has been limited, particularly in the abdomen and pelvis, due to the limited soft tissue resolution and lack of continuous intrafraction visualization of gross disease for x-ray based IGRT (e.g., CT and CBCT guidance). MR-linacs (MRLs) overcome these challenges by providing excellent soft tissue visualization through MR imaging, not only prior to but also continuously during treatment. In addition, online adaptive radiation therapy (oART) is routinely available on MRLs which may improve the safety of single-fraction SABR for tumors near certain organs-at-risk, such as gastrointestinal structures. Therefore, the objective of this prospective study was to evaluate the technical feasibility and safety profile of delivering MR-guided single-fraction SABR. We conducted a multi-center phase 2 trial (NCT04939246) of single-fraction 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 abdominal/pelvic lymph nodes (LNs) (25 Gy). oART was required to ensure that OAR constraints would be met based on the anatomy at the time of treatment. Continuous intrafraction soft tissue tracking of the target lesion and automatic beam gating were mandatory; breath hold was preferred to improve treatment efficiency. The primary objectives of the study included treatment feasibility (defined as a total in-room time (TIRT) <90 minutes for at least 80% of patients) and safety (defined as acute grade 3+ toxicity for <15% of patients and no grade 5 toxicity). Secondary objectives include 1-year local control, 1- year overall survival, quality-of-life, and late grade 3+ toxicity. Target accrual was 30 patients. Here we report the primary study endpoint. This study completed accrual of 30 patients treated to 32 lesions at 2 institutions in the United States between June 2021 and June 2023. 28 patients had a single lesion while 2 patients each had 2 lesions treated on study. Treated lesions were in the lung (n=11; 34.4%), adrenal gland (n=9; 28.1%), abdominal/pelvic lymph nodes (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 17/32 lesions (53.1%), 15 (88.2%) of which were in the abdomen or pelvis. Median TIRT and treatment delivery times were 53 minutes (range, 39-195 minutes) and 30 minutes (range, 15-144 minutes), respectively. TIRT was <60 minutes and <90 minutes for 21 patients (70%) and 25 patients (83.3%), respectively. TIRT was >90 minutes for 4 patients (median 116 minutes; range, 96-195). Median follow-up was 10.8 months (range, 0-12.8 months) from SABR. Acute grade 3 toxicity possibly related to study therapy Material/Methods: Results: