Toward adaptive proton therapy guided with a mobile helical CT scanner

• Published in: Radiotherapy and oncology 2018-12, Vol.129 (3), p.479-485
• Main Authors: Sun, Baozhou, Yang, Deshan, Lam, Dao, Zhang, Tiezhi, Dvergsten, Thomas, Bradley, Jeffrey, Mutic, Sasa, Zhao, Tianyu
• Format: Article
• Language: English
• Subjects: Adaptive radiation therapy; Imaging-guided proton therapy; In-room CT
• ISSN: 0167-8140; 1879-0887
• DOI: 10.1016/j.radonc.2018.08.021

•Daily imaging and frequent treatment adaptation are critically important for proton therapy.•A mobile helical CT scanner has been integrated into a compact proton treatment unit.•The present study demonstrates the feasibility of image guided adaptive proton therapy using a mobile helical CT scanner with superior imaging quality and a large field-of-view. To evaluate the feasibility of image-guided adaptive proton therapy (IGAPT) with a mobile helical-CT without rails. CT images were acquired with a 32-slice mobile CT (mCT) scanning through a 6 degree-of-freedom robotic couch rotated isocentrically 90 degrees from an initial setup position. The relationship between the treatment isocenter and the mCT imaging isocenter was established by a stereotactic reference frame attached to the treatment couch. Imaging quality, geometric integrity and localization accuracy were evaluated according to AAPM TG-66. Accuracy of relative stopping power ratio (RSPR) was evaluated by comparing water equivalent distance (WED) and dose calculations on anthropomorphic phantoms to that of planning CT (pCT). Feasibility of image-guided adaptive proton therapy was demonstrated on fractional images acquired with the mCT scanner. mCT images showed slightly lower spatial resolution and a higher contrast-to-noise ratio compared to pCT images from the standard helical CT scanner. The geometric accuracy of the mCT was