Abstract
PurposeTo describe the commissioning of AIRO mobile CT system (AIRO) for adaptive proton therapy on a compact double scattering proton therapy system.MethodsA Gammex phantom was scanned with varying plug patterns, table heights, and mAs on a CT simulator (CT Sim) and on the AIRO. AIRO‐specific CT‐stopping power ratio (SPR) curves were created with a commonly used stoichiometric method using the Gammex phantom. A RANDO anthropomorphic thorax, pelvis, and head phantom, and a CIRS thorax and head phantom were scanned on the CT Sim and AIRO. Clinically realistic treatment plans and nonclinical plans were generated on the CT Sim images and subsequently copied onto the AIRO CT scans for dose recalculation and comparison for various AIRO SPR curves. Gamma analysis was used to evaluate dosimetric deviation between both plans.Results AIRO CT values skewed toward solid water when plugs were scanned surrounded by other plugs in phantom. Low‐density materials demonstrated largest differences. Dose calculated on AIRO CT scans with stoichiometric‐based SPR curves produced over‐ranged proton beams when large volumes of low‐density material were in the path of the beam. To create equivalent dose distributions on both data sets, the AIRO SPR curve's low‐density data points were iteratively adjusted to yield better proton beam range agreement based on isodose lines. Comparison of the stoichiometric‐based AIRO SPR curve and the “dose‐adjusted” SPR curve showed slight improvement on gamma analysis between the treatment plan and the AIRO plan for single‐field plans at the 1%, 1 mm level, but did not affect clinical plans indicating that HU number differences between the CT Sim and AIRO did not affect dose calculations for robust clinical beam arrangements.ConclusionBased on this study, we believe the AIRO can be used offline for adaptive proton therapy on a compact double scattering proton therapy system.
Highlights
Patient weight loss, anatomical changes, and uncertainty in the stopping power of various tissues during proton therapy may cause beam range uncertainty that subsequently compromise tumor coverage and potentially increase dose to healthy tissue.[1]
It was noted that the low-density plugs have a higher CT number in the AIRO and the high-density plugs have a lower CT number when compared to the CT simulator (CT Sim) CT scan
This study shows that proton dose calculations on CT images sets from the AIRO mobile CT system can be used to calculate dose with relatively high accuracy similar to the clinically
Summary
Anatomical changes, and uncertainty in the stopping power of various tissues during proton therapy may cause beam range uncertainty that subsequently compromise tumor coverage and potentially increase dose to healthy tissue.[1]. We recently acquired and commissioned the AIRO Mobile CT System (Mobius Imaging LLC, Ayer, MA, USA) for patient localization and setup (3D IGPT) within the treatment room for our compact proton therapy system.[3]. The AIRO Mobile CT System (AIRO) has historically been used for intraoperative surgeries.[4] The small footprint (13.81 ft[2] when in scanning position) of the AIRO allows for CT acquisition in a compact proton therapy vault (Mevion S250, Mevion Medical Systems, Littleton, MA, USA) before or after treatment. The AIRO is a second generation, 32 slice helical CT scanner, capable of acquiring images with 120 kV, 10–250 mA, and field-of-view (FOV) up to 51.2 cm. The large FOV allows the scanner to capture the entire patient surface including immobilization devices and the treatment couch
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