2223 - Impact of a High Performance Imaging System on CTgART

R. Beckert¹, E. Laugeman¹, E. D. Morris¹, C. G. Robinson¹, A. Mo¹, H. Kim², T. Zhao³, and P. Samson¹; ¹Department of Radiation Oncology, Washington University School of Medicine in St. Louis, St. Louis, MO, ²Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, MO, ³Washington University School of Medicine in St. Louis, Department of Radiation Oncology, St. Louis, MO

Purpose/Objective(s): A high performance CBCT imaging system was recently commercially released for use on an O-ring gantry linear accelerator with online adaptive capabilities (CTgART). One potential limitation to online CTgART is limited soft tissue contrast. For this reason, prospective CTgART patients undergo a pre-treatment imaging-only CBCT simulation to evaluate clinical appropriateness of patient image quality for daily contouring. We hypothesize that the high performance CBCT imaging system increases the percentage of patients with CBCT simulations that are treated on the O-ring linac (adaptive and non-adaptive), and percentage treated with CTgART. Additionally, we investigated the impact of the high-performance imaging system on adaptive timing and total treatment times for a subset of CTgART patients. Materials/

Methods: The number of CBCT simulations pre-upgrade and post-upgrade were recorded. The percentage of patients that ended up being treated on the O-ring linac as well as the percentage of those patients that were treated with CTgART were determined. For CTgART patients that were treated with SBRT (= 5 fractions) and VMAT the nine months prior to the upgrade and all since the upgrade, the adaptive time (time from initial CBCT to pre-treatment verification CBCT) and total treatment time was recorded.
Results: From July 2021 to August 2023 (pre-upgrade), 139 CBCT simulations were completed. After upgrading to the high-performance CBCT imaging system (August 2023- February 2023), 67 CBCT simulations were completed. The percentage of patients with CBCT simulations that went on to be treated on the O-ring linac was 82.0% before the upgrade and increased to 95.5% with the high-performance imaging system. The percentage of patients with CBCT simulations that were treated with CTgART increased from 59.7% pre-upgrade to 77.6% with the high-performance imaging system. There were 122 SBRT VMAT CTgART evaluable sessions pre-upgrade and 93 sessions with the high-performance CBCT system. The mean adaptive time increased by 2.6 min, but was not statistically significant (34.5 to 37.1 min; p > 0.05) with the high-performance imaging system compared to pre-upgrade. Total treatment time also increased by 8.2 min.
Conclusion: The improvement in image quality with a high performance CBCT system has led to an increase in the percentage of prospective adaptive patients that pass through screening for CTgART; thus, increasing the number of patients that can benefit from the potential advantages of ART. At the same time, there has been an increase in adaptive and treatment time compared to pre-upgrade system. We hypothesize that the improved image quality has led to better visibility than pre-upgrade and has allowed for increased contour scrutiny. Additionally, patients with particularly difficult anatomy that may have been excluded before the upgrade are now eligible with improved image quality with a subsequent increase in contouring time.