Deterioration of pancreatic exocrine function in carbon ion radiotherapy for pancreatic cancer

BACKGROUND AND PURPOSE: In radiotherapy (RT) for pancreatic cancer, the pancreas is considered an important organ at risk. However, there are insufficient reports on pancreatic function deterioration after X-ray RT as organ at risk, and there are no reports on those after carbon ion (C-ion) RT. Here, we evaluated pancreatic exocrine insufficiency (PEI) after C-ion RT using dose-volume histogram (DVH) analysis. MATERIALS AND METHODS: Data were retrospectively collected from patients who had undergone C-ion RT for pancreatic cancer between July 2013 and June 2019. The prescribed C-ion doses were 55.2 Gy (relative biological effectiveness) in 12 fractions. Serum pancreatic amylase and lipase values were measured before and after C-ion RT. In DVH analysis, we assessed V(5Gy–50Gy) and V(<5)(Gy–50Gy) of pancreatic volume and analyzed whether these DVH parameters involved PEI. RESULTS: Thirty-three patients were included in the analysis. The median follow-up duration after the initiation of C-ion RT in these patients was 15.8 months (range, 4.3–64.8). During and after treatment, 57.6% of patients developed PEI within 13.6 months, defined as pancreatic amylase and lipase deficiencies. In DVH analysis, V(<5Gy) was the most effective factor for the PEI, and the cutoff value for developing PEI in V(<5Gy) was 4.57 cm(3). CONCLUSION: We showed that pancreatic exocrine function declined after C-ion RT for pancreatic cancer and that PEI was initiated early in the course of C-ion RT. Additionally, a low dose of DVH parameters, such as V(<5Gy), was a prognostic factor of PEI.