Author: Michelle Alonso-Basanta, Joshua Bryer, Lei Dong, Barbara Garcia, Elissa Khoudary, Brandon M. Koger, Taoran Li, Michael Salerno, Karen Tang, Boon-Keng Kevin Teo 👨🔬
Affiliation: University of Pennsylvania 🌍
Purpose: The Varian HyperSight imaging solution features a workflow for planning on CBCT images (CBCTp). This study evaluates the feasibility of CBCTp images in the setting of an offline adaptive planning workflow on the Halcyon system.
Methods: A cohort of 27 subjects were scanned mid-treatment using the Halcyon HyperSight imaging solution’s CBCTp mode with protocols designed for planning (CTDIvol=12-49mGy). Five subjects were used strictly for qualitative analysis of CBCTp image quality. The subject anatomic sites included head and neck, thoracic, genitourinary, gastrointestinal, gynecological, and breast. The CBCTp images reproduced patient setup according to the original planning CT simulation patient positioning. The plan approved for treatment was forward calculated to a registered CBCTp, evaluated by a physicist, and reviewed by a physician to determine if there was a need for adaptive therapy. Additionally, the original planning CT image was deformed to the CBCTp image to produce a synthetic CT reducing differences due to anatomical position. A dosimetric comparison between the CBCTp and synthetic CT-based plan was performed to assess relative target coverage and organ at risk sparing.
Results: Clinically significant changes triggered adaptive therapy for five patients for all anatomic sites except the thorax and breast. Dosimetric quality of plans using CBCTp images displayed comparable target coverage and sparing of OARs to the “deformed” (synthetic) planning CT. CBCTp appointment times ranged 12-33 minutes (average: 20 minutes).
Conclusion: The Hypersight CBCTp workflow on Halcyon offers an approach to offline adaptive treatment planning with appointment times to 1 hour CT simulation slots and comparable CTDIvol to CT simulation scanning protocols. It adds flexibility to clinic schedules by allowing patients to receive a CBCTp scan at the treatment machine with HU accuracy and dosimetric quality comparable to CT simulation images.