3454 - Impact of Subcutaneous and Visceral Fat in Patients Receiving Ablative Stereotactic MR-Guided Adaptive Radiotherapy for Pancreatic Cancer
Presenter(s)
A. Kaiser1,2, N. Ud Din1,3, D. Faught4, L. Hodgson5, R. Herrera1, M. D. Chuong3, and K. E. Mittauer3; 1Miami Cancer Institute, Miami, FL, 2Florida International University, Herbert Wertheim College of Medicine, Miami, FL, 3Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, FL, 4MIM Software, Inc., Beachwood, OH, 5Miami Cancer Institute Baptist Health South Florida, Miami, FL
Purpose/Objective(s): A high ratio of subcutaneous fat (SF) to visceral fat (VF) has been shown to correlate with favorable outcomes after chemotherapy in advanced pancreatic ductal adenocarcinoma (PDAC). We hypothesized that a similar relationship may exist with radiation. Here we examined the prognostic impact of the SF to VF ratio (SVR) in non-metastatic PDAC patients receiving stereotactic MR-guided adaptive radiation therapy (SMART).
Materials/Methods: We retrospectively analyzed consecutive patients with borderline resectable or locally advanced PDAC who received SMART between 2021 and 2024. SVR was calculated by quantifying VF and SF areas (cc) on a single 0.35 T MR simulation scan slice at the L2 mid-vertebral body level using a semi-automated segmentation workflow. VF and SF contours were reviewed and edited by a radiation oncologist. SVR was then compared to patient characteristics and disease outcomes. Progression free survival (PFS) and overall survival (OS) were estimated from diagnosis with the Kaplan-Meier method. Cox proportional hazards regression model was used for group comparisons and the z-statistics test was utilized for survival outcomes.
Results: Fifty patients with a median age of 72 years (range, 21 - 92) were evaluated. The majority were male (54%) with T4 primaries (72%) and were node negative (72%). Median tumor size was 3.6cm (range, 1.5 - 9.0) with pre-SMART median CA19-9 of 38 (range, 1.2 - 1933). Nearly all were prescribed 50 Gy by SMART (98%) and completed neoadjuvant chemotherapy (90%). A minority underwent pre-SMART irreversible electroporation (6%) or post-SMART resection (6%). Most were never smokers (58%), ECOG 0-1 (92%), non-diabetic (78%) with median BMI of 24.3 kg/m2 (range, 17.1 - 41.5). Median SVR was 0.5 (range, 0.2 - 1.4) with high SVR (> 0.37) in 72% and low SVR (= 0.37) in 28%. High SVR were typically never smokers (p=0.021), female (p=0.013), and harbored smaller primary tumors (median 3.3 vs. 4.2cm, p=0.036), but did not differ in BMI or other factors. Median PFS was 15.6 months (range, 12.9 - 18.3) with median OS of 22.0 months (range, 17.4 - 34.3). High SVR showed a near statistically significant trend towards improved survival with 2-year OS of 23.8% vs. 49.9% for low vs. high SVR, respectively (p=0.065). There was no correlation between PFS and SVR.
Conclusion: High SVR is associated with a doubling of 2-year OS (23.8% vs. 49.9%) in patients with non-metastatic PDAC treated with ablative radiation after neoadjuvant chemotherapy. This relationship met only near statistical significance due to the small size of the study cohort. The OS benefit was unrelated to PFS, indicating that SVR may be an independent marker of all-cause mortality in this patient population. Larger, prospective data is needed to validate this preliminary finding, which may have important implications in survivorship strategies to optimize PDAC outcomes.