723 Background: Carbon-ion radiotherapy (C-ion RT) for pancreatic cancer is commonly administered at an RBE-weighted dose of 55.2 Gy in 12 fractions; however, local tumor control remains insufficient. To overcome this limitation, we initiated a phase I clinical trial employing intensity-modulated ion therapy with a simultaneous integrated boost (SIB) strategy combined with linear energy transfer (LET) optimization, aiming to evaluate the tolerability of dose intensification using these approaches. Methods: Patients with histologically confirmed non-metastatic pancreatic cancer were eligible. Dose-limiting toxicity (DLT) was defined as Grade ≥3 non-hematological or Grade ≥4 hematological events occurring within 90 days from the start of treatment. The high-dose clinical target volume (CTV2) included the gross tumor and regions at high risk for recurrence, while CTV1 encompassed CTV2 and elective nodal areas. Treatment consisted of 12 fractions in three weeks, delivering 43.2 Gy to CTV1. CTV2 received escalating doses from 55.2 Gy to 67.2 Gy in four levels. LET distribution within CTV2 was optimized to ≥44 keV/μm. This single-institution, phase I trial adopted a conventional 3 + 3 design. Results: Twelve patients were enrolled (median age, 67 years; range, 37–80). Tumor sites included the head (n=4) and body/tail (n=8). Eleven patients had stage III disease, and one had stage IB; all were deemed unresectable. Treatment was completed in all cases without interruption. No DLTs were reported. The 1-year local control and overall survival rates were both 92%. Conclusions: Dose escalation of C-ion RT for unresectable pancreatic cancer using the SIB method with LET optimization, up to 67.2 Gy in 12 fractions, proved feasible and safe. Based on these results, a multicenter phase II trial is being planned to validate this regimen, with 67.2 Gy/12 fractions as the recommended dose. Clinical trial information: jRCTs032210292 .
Shinoto et al. (2026) studied this question.