Stereotactic ablative radiation for pancreatic cancer on a 1.5Telsa magnetic resonance-linac system.

Abstract

Ablative radiation therapy (A-RT) appears to improve outcomes in locally advanced pancreatic cancer (LAPC) yet requires solutions for respiratory and digestive motion. We report outcomes of A-RT for pancreatic cancer using 1.5T MR-adaptive treatment delivery. Between March 2020 and July 2021, we treated 30 patients with pancreatic cancer with 50Gy in 5 fractions (biologically effective dose [BED10]=100Gy10) using a novel compression belt workflow and remote planning on the Unity 1.5T MR linac system. Cumulative incidence of progression was computed from A-RT initiation with death as a competing risk. Overall (OS) and progression-free survival (PFS) were calculated using Kaplan Meier methods. Of 30 patients, most (73%) were locally advanced, 4 (13%) were metastatic, 2 (7%) were medically inoperable, and 2 (7%) were locally recurrent. Most (73%) received FOLFIRINOX prior to A-RT. Median follow-up times from diagnosis and A-RT were 17.6 (IQR 15.8-23.1) and 11.5months (IQR 9.7-16.1), respectively. Cumulative incidences at 1-year of local and distant progression were 19.3% (95%CI 6.7-36.8%) and 47.4% (95%CI 26.7-65.6%), respectively. Median OS from diagnosis and A-RT were not reached. One-year OS from diagnosis and A-RT were 96.4% (95%CI 77.2-99.5%) and 80.0% (95%CI 57.3-91.4%), respectively. Median and 1-year PFS were 10.1months (95%CI 4.4-14.4) and 39.7% (95%CI 20.3-58.5%), respectively. No grade 3+toxicities were observed. A-RT using the 1.5T Unity MR Linac resulted in promising LC and OS with no severe toxicity in patients with LAPC despite radiosensitive organs adjacent to the target volumes. Longer follow-up is needed to assess long-term outcomes.