SU-E-T-814: Dosimetric Feasibility of Dose Escalation with Gated IG-IMRT for Pancreatic Cancer

Abstract

Purpose: Delivery of curative high dose to the pancreatic tumor is limited by the surrounding radiation sensitive organs at risk (OARs), especially the most dose‐limitingorgan duodenum. Image‐guidedradiotherapy(IGRT) allows small planning target volume (PTV) margin and intensity‐modulated RT (IMRT) offers sharp dose gradients, permitting dose escalation with minimal OAR damage. We study the dosiemtric feasibility for using IG‐IMRT to escalate dose to pancreatic cancer. Methods: Planning 4D CT datasets for 10 pancreatic cancer patients treated previously were used for evaluation. A PTV margin of 3 mm was added to the clinical target volume (CTV, pancreatic head). This small margin is justified because the patient is to be treated with (1) gating to reduce the intrafractional (respiration) motion below 3 mm, and (2) high quality CT guided repositioning using an in‐room CT (e.g., CTVision, Siemens) to minimize interfractional variations. IMRT plans with prescription doses of 50.4 Gy and 72 Gy in 1.8 Gy fractions were generated using a planning system (Panther, Prowess). Results: A series of dose volume quantities at two prescription doses 50.4 and 72 Gy were compared. For six out of 10 patients, the duodenum volumes irradiated by at least 50.4 Gy (V50.4 Gy) with the prescription dose of 72 Gy are well below 50%, while the doses to other OARs are within the acceptable ranges. for two (seven) out of 10 patients the volumes irradiated by at least the prescription dose of 72 Gy are less than 5 (10) cc. Conclusions: With appropriate selection of patients with pancreatic cancer, the dose escalation to 72 Gy may be feasible by using gated IMRT with daily in‐room CT guidance.