P276] Impact on proton range estimates using a novel mr-based artifact reduction algorithm

Abstract

Purpose Metal implants lead to streak and cupping artifacts in computed tomography (CT) images, causing erroneous CT number estimates for radiation therapy (RT) planning. We recently introduced kerMAR, a novel Magnetic Resonance (MR)-based CT metal artifact reduction algorithm that combines kernel regression on uncorrupted CT value/MR patch pairs with a forward model of the CT metal artifacts. Here, we compare the impact of kerMAR and the clinical oMAR algorithm (Philips) on the proton range in calculated spot scanning (SS) dose plans for proton RT. Methods We acquired T1w MR and CT image sets of a veal shank phantom with and without metal markers inserted, and applied kerMAR and oMAR to the former. We then created SS plans in Eclipse v. 13.7 (Varian) delivering 150 MeV protons in a 0.55 cm single spot that passed 1) near a metal marker at shallow depth and 2) near two different markers located at shallow (near bone) and deep depths, respectively. Similar images were acquired for 4 head-and-neck (HN) RT patients with dental implants, and plans using the same phantom beam, angled through the artifact corrupted oral cavity, were devised, leading to a configuration most resembling phantom beam 2. We finally recalculated the dose plans for the same beamline settings and monitor units on all CT sets, and compared the proton ranges defined as the depth with 80% of the maximum dose. Results For the phantom plans, the following range deviations relative to the metal-free reference plan (uncorrected CT, oMAR, kerMAR) were observed: Plan 1: (0.6, 0.6, 0.6)%; plan 2: (−4, −1.8, −2.1)%. The patient plans showed the following deviations from the uncorrected CT plan: kerMAR: (10, 8, −7, 11)%; oMAR: (3, 0.1, −10, 0.2)%. Conclusions Proton range calculations on a phantom showed similar improvements compared to the uncorrupted reference with kerMAR and oMAR. Similar calculations on HN patients, however, displayed systematic proton range increases when applying kerMAR as compared to oMAR.