Clinical Outcomes with Low-field MR-Guided Radiation Therapy (MRgRT) for Pancreatic Cancer

Summary: This study evaluates the efficacy and safety of ablative stereotactic magnetic resonance (MR)-guided adaptive radiation therapy (SMART) in locally advanced pancreatic ductal adenocarcinoma (PDAC). The aim was to assess the impact of daily adaptive planning with ablative doses (BED10 = 100 Gy) on tumor volume dynamics, treatment response with CA 19-9 levels, and clinical outcomes. Sixteen patients (56% women, median age 76.5 years) were treated with SMART; fifteen (94%) underwent treatment delivering 50 Gy in 5 fractions (BED10 = 100 Gy), while one patient (6%) was treated with 50 Gy in 4 fractions. All patients underwent daily adaptive treatment for each fraction. We analyzed: 1) changes in gross tumor volume (GTV) over the treatment course including a) inter-observer variability in GTV delineation and b) GTV changes across tumor location and 2) dynamics of CA 19-9 levels before, during, and after treatment. The median percent change in GTV volume from the first to final fraction was 1.09% (range, -17.20-26.56%). Inter-observer variability in GTV delineation resulted in a mean coefficient of variation of 6.89% (range: 0-21.3%). We observed no significant difference in percent GTV change among the five different tumor stages (p = 0.679, F(4,11) = 0.587). In addition, we observed no significant difference in percent GTV change inter-fractionally between GTV contours traced by the primary physician and the alternative (p= 0.8407, W= 625). The one-year overall survival rate was 81.25%, which is significantly higher than the reported 50-60% in previous studies of locally advanced PDAC treated with conventional radiotherapy (p=0.001). This study demonstrates the potential effectiveness of SMART in locally advanced PDAC, achieving significantly higher one-year survival rates compared to conventional approaches. Observed tumor volume dynamics provide valuable insights for adaptive planning strategies. These findings warrant larger, prospective studies to optimize MR-guided adaptive radiotherapy and potentially improve outcomes for this challenging disease. Lunya Allie (she/her/hers), n/a (Presenting Author) - Washington University in St. Louis; James Sohn (he/him/his), PhD (Co-Author) - University of Chicago; Caleb Song (he/him/his), n/a (Co-Author) - University of Chicago; Ethan Stolen (he/him/his), B.A. (Co-Author) - University of Chicago; Yirong Liu (she/her/hers), MD, PhD (Co-Author) - Northwestern University; Tarita Thomas (she/her/hers), MD (Co-Author) - Northwestern University