Commissioning an in‐room mobile CT for adaptive proton therapy with a compact proton system

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.

Commissioning and beam characterization of the first gantry‐mounted accelerator pencil beam scanning proton system

“…The gantry has a maximum rotation of 190° degrees from −5° to 185°, combined with a 6‐D robotic couch that can rotate 270°, supporting almost all the treatment angles through couch rotation. IGRT is supported with the use of a pair of orthogonal planar kV imagers through high precision bony anatomy or fiducial alignment, and an in‐room mobile diagnostic‐quality CT scanner for 3D volumetric imaging, which enables adaptive radiation therapy …”

“…IGRT is supported with the use of a pair of orthogonal planar kV imagers through high precision bony anatomy or fiducial alignment, and an inroom mobile diagnostic-quality CT scanner for 3D volumetric imaging, which enables adaptive radiation therapy. 22…”

Comparison of MR‐guided radiotherapy accumulated doses for central lung tumors with non‐adaptive and online adaptive proton therapy

“…In-room CT scanners are already installed at a few proton therapy centers. 11,[30][31][32] Also CBCT scanners are becoming more widespread in proton therapy facilities, 11 and several methods to correct the acquired CBCT images for artifacts and rescale the image intensities to allow accurate dose calculations have been proposed in the literature. [33][34][35] MR-guided proton therapy is a promising future treatment modality, [36][37][38][39] and first prototype systems have been constructed.…”

Online daily adaptive proton therapy

“…21 Therefore, there is a growing interest also in the proton therapy community to clinically implement an online daily adaptive proton therapy (DAPT) workflow, to properly cope with interfractional changes. [24][25][26][27] For intrafractional changes, an even more frequent imaging acquisition and a faster plan adaptation procedure (in real time) is needed. [28][29][30] Since the latter is an interesting research topic but still farther from clinical implementation, in this review we focus on the ongoing research of online DAPT.…”