Author: Theodore Higgins Arsenault, Kenneth W. Gregg, Lauren E Henke, Rojano Kashani, Haley K Perlow, Alex T. Price, Atefeh Rezaei, Prashant Vempati, Runyon C. Woods 👨🔬
Affiliation: University Hospitals Seidman Cancer Center 🌍
Purpose: The HyperSight imaging feature on C-arm linacs(HS-CBCT) offers increased CT number accuracy over conventional on-board imaging. The C-arm geometry allows for noncoplanar treatments common to stereotactic radiosurgery(SRS) leading to better fall-off and low-dose spreading compared to coplanar treatments. Direct-to-unit(DTU) SRS treatment advantages include mitigation of setup and registration errors between MRI and CT-sim at the linac, shorter single-visit treatments, and lower imaging dose. We aim to demonstrate the initial feasibility of a DTU SRS approach.
Methods: Scans were acquired for four patients with brain or head-and-neck malignancy, including one post-operative patient with metal implant, enrolled in an IRB-approved clinical trial for in-vivo image quality on TrueBeam v4.1 using HS-CBCT. OARs were propagated from CT-sim to the HS-CBCT using a rigid registration. One to five target volumes were created or propagated for four patients to resemble SRS lesions. Single-isocenter VMAT plans were developed with arcs at three couch angles in RayStation with 0.1cm dose grid on a clinical Varian Edge model and calculated on both CT-sim and HS-CBCT. Dose between scans were compared using 3D gamma analysis at 1%/1mm local, 10% thresholding and percent difference in target dose-volume histogram metrics(DVHM).
Results: Three plans met the same clinical goals in CT-sim and HS-CBCT calculations. A five-target treatment plan failed one more clinical goal for brainstem after recalculating on HS-CBCT. When comparing dose per scan, the worst-case 3D gamma pass rate was 99.6%. Target DVHM worst-case was GTV-D99 +1.6% difference to CT-sim dose calculations.
Conclusion: High 3D gamma pass rates and <2% deviation in target DVHM suggest excellent agreement in dose calculations. This study demonstrates that utilization of advanced on-board imaging technology could benefit SRS patients via DTU capabilities. Future work includes development of automated planning tools to aid online planning for a single-visit SRS workflow.