Multi‐Institutional Phase II Study on the Efficacy and Safety of Dynamic Tumor‐Tracking, Moderately Hypofractionated Intensity‐Modulated Radiotherapy in Patients With Locally Advanced Pancreatic Cancer

BACKGROUND: For delivering high radiation doses to pancreatic tumors, organ motion management is indispensable; however, studies on this are limited. We aimed to evaluate the efficacy and safety of dynamic tumor tracking (DTT) moderately hypofractionated intensity-modulated radiotherapy (IMRT) in patients with locally advanced pancreatic cancer (LAPC). METHODS: Patients with histological confirmation for LAPC were included. A linac system, which was mounted with a gimbal function, was used for DTT-IMRT. The prescribed dose was 48 Gy in 15 fractions. The primary endpoint was the 1-year rate of freedom from locoregional progression (FFLP). RESULTS: DTT-IMRT was successfully administered in 25 patients enrolled from four institutions. The median range of respiratory motion during DTT-IMRT was 9.8 mm (range: 3.5-27.3 mm), and the median tracking accuracy was 2.6 mm (range: 0.7-5.2 mm). With a median follow-up period of 13.9 months, the 1-year FFLP rate was 75.3% (lower limit of one-sided 80% confidence interval [CI]: 60.2%), which satisfied the predetermined primary endpoint. One-year locoregional progression-free survival, progression-free survival, and overall survival were 56.0% (95% CI: 34.8%-72.7%), 44.0% (95% CI: 24.5%-61.9%), and 60.0% (95% CI: 38.4%-76.1%), respectively. Regarding nonhematologic toxicities, grade 3 acute gastrointestinal (GI) toxicity was observed in two patients (8%), and two patients (8%) each experienced grade 3 late GI and non-GI toxicities. No grade 4 or 5 nonhematologic toxicities were observed. CONCLUSIONS: DTT moderately hypofractionated IMRT shows preferable locoregional control without significant toxicity in patients with LAPC. TRIAL REGISTRATION: UMIN000017521.