Simulation study of dosimetric effect in proton beam therapy using concomitant boost technique for unresectable pancreatic cancers.

Abstract

The purpose of this study is to investigate the dose distribution of proton beam therapy (PBT) using a concomitant boost technique for unresectable pancreatic cancers. This simulation study involved 36 patients with unresectable pancreatic cancer. The irradiation dose was set as 67.5 gray equivalent (GyE) with 25 fractions using concomitant boost technique. The irradiation dose was set as 50 GyE to cover the whole target and another posterior beam of 17.5 GyE was added to ensure that 10% isodose line was not delivered to the gastrointestinal (GI) tract. Dose distribution of the gross tumor volume and GI tract was examined. V55GyE, 60GyE, 65GyE were 80.8, 66.5, and 42.4%, respectively, and mean dose was 64.1 GyE in all patients. The distance from the GI tract showed significant difference in dose distribution (P = 0.002 in V55GyE, 0.0009 in V60GyE, 0.003 in V65GyE, and 0.02 in mean dose, respectively). Location, tumor diameter, or lymph nodes metastasis did not show any difference. We found that irradiated dose is closely related to the distance from the GI tract. Clinically, this protocol is expected to have outstanding effects on local control of tumors compared to conventional PBT.