Intensity Modulated Arc Radiotherapy (IMAT) Planning for Patients with Pancreatic Cancer: A Planning Study

Abstract

Background: Intensity-modulated arc therapy (IMAT; RapidArc, Varian®) has been described as allowing the delivery of highly conformal dose distribution to complex shaped radiation target volumes. Here we investigate IMAT related target volume coverage and normal tissue dose exposure in patients with pancreatic cancer, in comparison with established static beam delivery techniques. Materials and methods: A retrospective planning study was performed in 20 patients with pancreatic cancer who had previously undergone radiation therapy following Whipple resection with risk factors for local tumor recurrence (n=12), or were considered unresectable (n=8). Based on 4DCT simulation imaging, the internal target volume (ITV) was delineated and expanded by 5 mm into a planning target volume (PTV). Treatments were planned in 2 phases, with initial planning to 45 Gy in 25 fractions, followed by re-simulation and boost planning to a total dose of 59.4 Gy (dose prescribed to 95% of the PTV). Three different treatment planning techniques were compared 3D, IMRT (the clinically used plan), and IMAT. To determine cumulative doses delivered during the 2 courses of radiotherapy, deformable registration between CT data sets was performed (Velocity Medical Solutions®). DVH parameters were obtained for the PTV (Dmean), and organs at risk (OAR; kidneys Dmean, kidney V15 and V20, liver Dmean, Liver V30; spinal cord Dmax). Conformity indices were computed for various dose levels (Fig.3). For statistical analysis, two-way comparisons were performed using the Wilcoxon signed ranks test (significance level: p<0.05).