Dosimetric Validation of Hypersight-Based Online Adaptive Radiotherapy on a C-Arm Linac Using Iroc Phantoms
Abstract
Purpose
To validate an online adaptive radiotherapy (oART) workflow for a C-arm linear accelerator (LINAC) equipped with HyperSight CBCT using Imaging and Radiation Oncology Core (IROC) anthropomorphic phantoms.
Methods
An adaptive workflow was implemented on a TrueBeam linac using the Eclipse planning environment. The protocol utilizes contours and a preplan generated on a prior CT scan. Daily HyperSight CBCTs were registered to the prior CT, followed by contour propagation and plan re-optimization directly on the CBCT scan. Dosimetric validation was performed using IROC Head & Neck, Prostate, and Lung motion (gated at 40-60% exhale) phantoms. Each phantom was positioned with offsets, imaged, re-optimized, and irradiated. Accuracy was assessed via IROC’s independent TLD and radiochromic film analysis. Verification plans were generated on reference CTs for comparison.
Results
HyperSight image quality exhibited sufficient Hounsfield Unit (HU) stability for direct computation, matching diagnostic CT within 1.5% for soft tissue. All three adaptive deliveries successfully passed the IROC IMRT credentialing audit. TLD measurements showed excellent agreement (0.96-0.99) between delivered and calculated dose, falling well within IROC acceptance limits. Radiochromic film analysis demonstrated gamma pass rates of 99-100% for all planes in all anatomical sites, confirming spatial accuracy of dose distributions. Feasibility was demonstrated with total procedure times (setup to beam-on) of 40–60 minutes for all sites, achieved without prior practice sessions. Comparison of dose distributions between HyperSight and standard CT plans demonstrated excellent 3D gamma passing rates across various criteria.
Conclusion
This study validates the dosimetric accuracy of a HyperSight-based online adaptive workflow on a standard C-arm linac. By enabling direct dose calculation on CBCT, this method opens the possibility of performing online adaptive RT on a C-arm LINAC, offering a clinically viable and versatile alternative to dedicated ring-gantry adaptive systems.