2966 - A Retrospective Analysis of the Treatment Time of CBCT-Based Online Adaptive SBRT: A Single Institute's Experience

Purpose/Objective(s): There is an increasing interest in CBCT-based online adaptive SBRT (OA-SBRT) as daily anatomical variations may favor dose sparing of critical organs. However, as OA-SBRT session involves a whole workflow from imaging/contouring to plan delivery, it results in a much longer patient on-table time than conventional SBRT. This waiting time becomes an important consideration for patient care as patients remain immobilized for extended periods. This study is to evaluate the treatment time of CBCT-based OA-SBRT to provide clinically relevant data for optimizing logistics and improving patient care in OA-SBRT programs.

Materials/Methods: Adaptive SBRT treatment records were retrieved from an Ethos system. Data includes two time points: one within the first 2 months of the OA-SBRT program and the other at one year after the program. For each time point, the dataset includes two treatment sites (prostate and abdomen, each with n=15 sessions). An OA-SBRT session was divided into 4 steps/tasks: (1) 1^st CBCT acquisition & contouring; (2) plan optimization & calculation; (3) plan review & physics QA; (4) 2^nd CBCT review & plan delivery. The time spent on each step was analyzed by using the timestamp in the Dicom files generated after each step.

Results: For the first 2 months of the OA-SBRT program, the task time for 1^st CBCT&contouring is 9.1±3.5 mins (prostate) vs. 23.3±7.8 mins (abdomen). After one year, it becomes 9.2±3.9 mins (prostate) vs. 19.6±11.2 mins (abdomen). The total session time is 22.2±3.2 mins (prostate), 45.5±7.0 mins (abdomen) in the first 2 months, and 23.1±4.8 mins (prostate), 39.9±12.1 mins (abdomen) after one year. For other steps, the task time is quite consistent between the two time points as well as the two treatment sites, e.g., 1.6-2.2 min for plan optimization & calculation, 5.4-7.2 min for plan review & physics QA. The time for 2^nd CBCT & plan delivery is about 5.7-12.4 mins, which depends on the prescription dose and delivery techniques.

Conclusion: Contouring time is the primary contributor to the overall OA-SBRT procedure time and varies by treatment site. Abdominal OA-SBRT took a longer time than prostate OA-SBRT as the anatomy is more complicated for abdomen. However, it improved with gaining experience. Overall, prostate OA-SBRT took ~25 mins, and abdominal cases took ~40-50 mins (non-gated/non-breath-hold treatment).