Evaluation of dose calculation accuracy of HyperSight CBCT imaging system for adaptive radiotherapy in SBRT prostate cancer patients

Abstract

Adaptive radiotherapy (ART) involves adjusting the treatment plan according to daily anatomical changes, especially in prostate patients who were treated with the stereotactic body radiotherapy (SBRT) technique. The recent development of the new CBCT imaging system, equipped on the Ethos machine called HyperSight, offers better image quality, more accurate CT number, and shorter acquisition time (5.9 s). This research aims to investigate the accuracy of daily dose treatment based on HyperSight CBCT (HS-CBCT) compared with planning CT (pCT) for SBRT prostate cancer patients in an ART workflow.The image quality of HS-CBCT was evaluated using Catphan604 compared with pCT. The calibration curve was established between electron density and CT number against pCT to assess CT number accuracy using the CIRS CBCT electron density phantom. The daily HS-CBCT were registered to pCT and recalculated dose directly on HS-CBCT to generate adaptive plans (ADPs) and schedule plans (SCHs). Dosimetric differences of 35 ADPs from 7 patients were investigated using dose-volume histogram (DVH) parameters and gamma analysis.HyperSight CBCT demonstrates the enhancement of image quality and CT number accuracy within ±31 HU. The calibration curve of HS-CBCT closely matches the pCT, particularly in the planning mode. For the patient cohort, HyperSight enabled accurate dose calculation as pCT. The average (±SD) dose of PTV V100% was 98.04 ± 0.97%, which was significantly improved in ADPs (p<0.05), except for bowel. Additionally, the dose distribution of ADPs showed a gamma passing rate ≥ 95% for 3%/2 mm with 10% threshold. HyperSight provides good image quality and CT number accuracy. Thus, HyperSight has the potential to be an alternative image used for dose calculation directly on HS-CBCT in the ART workflow, particularly in prostate cancer.