Dose escalation study with respiratory-gated carbon-ion scanning radiotherapy using a simultaneous integrated boost for pancreatic cancer: simulation with four- dimensional computed tomography

Objective: Pancreatic cancer is a difficult to treat disease with a persistently high mortality rate. We evaluated dose distribution simulation with respiratory-gated carbon-ion pencil beam scanning (C-PBS) with a simultaneous in- tegrated boost (SIB) to increase tumour dose, sparing organs at risk (OARs).Methods: Using four-dimensional CT data of 12 patients, we delineated gross tumour volume and two clinical target volumes (CTVs). To consider beam range intra- fractional uncertainty, we calculated field-specific target volumes, from which two planning target volumes (PTVs) were generated. PTV1 would receive a planned dose of 55.2 Gy [relative biological effectiveness (RBE)-weighted absorbed dose] in 12 fractions, and PTV2 would receive an SIB dose up to 67.2 Gy (RBE). Dose assessments were conducted with regard to the targets and OARs.Results: CTV2 dose covering 95% of the volume (D95%) increased from 50.3 6 5.1 Gy (RBE) to 62.5 6 3.5 Gy (RBE) for a planned dose from 55.2Gy (RBE) to 67.2Gy (RBE). For 4 of 12 patients with a distance of $5mm between the tumour and the gastrointestinal tract, CTV2 D95% was $95% of planned dose at all dose levels.Conclusion: We quantified dose escalation with respiratory-gated C-PBS using SIB for pancreatic cancer and revealed that OAR dose was not affected to the same degree as the tumour dose.Advances in knowledge: A simulation study on respiratory- gated C-PBS with SIB for pancreatic cancer was per- formed. The results indicated the feasibility of dose escalation for pancreatic cancer, which should be con- firmed in clinical trials