CT-on-Rails Utilization for Image Guidance and Plan Adaptation at a Single-Room Proton Therapy Center.

Abstract

In-room CT-on-rails is a relatively rare imaging modality in proton therapy. This work evaluated the utilization of CT-on-rails (CTOR) for image guidance and plan adaptation at a single-room proton therapy center. All patients treated from the proton center beginning treatment to the current date were evaluated (May 2021 - January 2023). Patients were treated using a Mevion S250i scanning beam proton therapy system with an in-room Definition Edge CTOR. The image guidance technique utilized for each patient was evaluated (CTOR, orthogonal planar kV imaging, or both). For patients who required a new CT for plan adaptation, the use of CT images from CTOR or a new simulation CT was assessed. Of the 132 patients treated over the evaluated time period, 56.0% utilized CTOR for image guidance at some point during their treatment. 21.2% utilized CTOR as the only image guidance technique, while 34.8% utilized CTOR in combination with kV planar imaging. For 43.9% of patients, only orthogonal planar kV imaging was utilized. Head and neck treatment sites most often utilized CTOR alone as an image guidance technique, while central nervous system sites most often utilized kV planar imaging alone. Of the patients who required new CT imaging for plan adaptation, 75.0% utilized CTOR images. Some reasons for patients not being able to utilize CTOR imaging for re-planning were the need for 4DCT imaging (which was not available on the CTOR) or the need to re-make immobilization devices (such as thermoplastic masks due to becoming loose). CTOR was shown to be utilized for image guidance in the majority of patients receiving proton therapy at a single-room proton therapy center. CTOR was able to be used for plan adaptation in a large majority of patients, eliminating the need to schedule additional CT simulation appointments for these patients.