Session Item

To evaluate clinical outcomes of patients with locally advanced pancreatic cancer (LAPC) treated with high-dose stereotactic ablative body radiotherapy (SABR), and determine dose parameters correlated with treatment outcomes and adverse events.

A single institution cohort of 51 patients with LAPC treated with high-dose SABR (≥40 Gy) between 2017 and 2020 was retrospectively analyzed. Majority of the patients underwent induction chemotherapy (92.2%) for a median of 13 cycles (range, 4-29 cycles) before SABR, and had partial response in 56.9% of patients, stable disease in 19.6%, and progressive disease in 15.7%. Median prescribed dose was 50 Gy (range, 40-50 Gy) delivered in 5 fractions in all patients. Twenty-eight (54.9%) patients underwent daily adaptive SABR using magnetic resonance imaging guidance and 23 (45.1%) patients underwent linac-based non-adaptive SABR. GTV D_min and GTV D_max were defined as the minimum and maximum dose absorbed by 1cc of the GTV, respectively. Overall survival (OS), progression-free survival (PFS), freedom from loco-regional progression (FFLP), and freedom from distant progression (FFDP) were calculated from the start date of SABR.

With a median follow-up of 14.6 months (range, 3.2-56.9) after SABR, the 1-year and 2-year OS rates were 71.5% (95% CI, 56.0%-82.4%) and 47.4% (95% CI 31.3%-61.9%), respectively. The 1-year and 2-year cumulative incidence of loco-regional progression were 13.2% (95% CI, 6.1%-27.2%) and 45.4% (95% CI, 29.7%-64.6%), respectively. All nine (17.6%) patients who underwent resection had R0 resection. On multivariate analysis, longer duration of induction chemotherapy (>3 months) and greater CA 19-9 decline after SABR (>50%) were associated with improved OS and PFS (all p<0.05). Response to induction chemotherapy showed significant association with PFS and FFDP (all p<0.05), and a trend toward improved OS (p=0.098). Among patients with oligometastatic cancer, response to induction chemotherapy showed a significant association with OS (p=0.009). GTV D_min ≥50 Gy was related with significantly improved FFLP (p=0.019) and PFS (p=0.031), whereas prescribed dose and GTV D_max were not. Grade 2 and 3 late toxicities occurred in 12 (23.5%) and 3 (5.9%) patients, without grade 4 or higher event. Dose to the organ at risk (D_max <38 Gy and D_1cc <34 Gy) was significantly related with grade ≥2 late event. MRI-guided adaptive RT showed the fewer trend of grade 3 late toxicity (3.6% vs. 8.7%, p=0.398)

High-dose SABR is an effective treatment option for LAPC patients with favorable clinical outcomes and minimal interference with systemic therapy. Prospective randomized trial incorporating SABR is warranted to further elucidate the role of radiotherapy in patients with LAPC.