2415 - Optimizing Online CBCT-Based Adaptive System Capacity Utilizing an APRT

Purpose/Objective(s): Adaptive efficiency is a key driver for online adaptive radiotherapy (oART) to become more mainstream, as oART is a time-consuming and resource-intensive process, and most centers need to balance adaptive and non-adaptive schedules in a hybrid format on treatment units. This study analyzed the effect on total treatment time of an advanced practice radiation therapist (APRT) for oART contouring and potential impact on hybrid machine scheduling.

Materials/Methods: Total treatment times, from patient setup to treatment completion, were collected for oART utilizing a CBCT-based adaptive system equipped with advanced CBCT imaging. All timing data were stratified and compared based on if the individual APRT was present/contouring or if one of a team of radiation oncologists (RO) was the primary adaptor with no APRT help. Adaptive cases were then categorized into two groups: Non-Gated and Gated, which utilized surface guided breath hold treatments.

Adaptive treatment time slots were calculated based on the 90^th percentile for Non-Gated APRT-led, Non-Gated RO-led, Gated APRT-led, and Gated RO-led. A hypothetical treatment schedule was generated based on calculated treatment time slots. A 10 hour workday (600 minutes) was assumed with up to 300 minutes (half-day) designated for adaptive cases. All remaining non-adaptive time slots were set at 15 minutes (based on our institutional scheduling). Differences in daily schedules were projected over a calendar year.

Results: Over 19 months, 1019 adaptive SBRT fractions were evaluated on 217 unique patients (130 Non-Gated vs. 889 Gated). Table 1 shows the calculated 90^th percentiles and scheduled treatment time slots. Based on 90^th percentile, APRT-led Non-Gated cases could be scheduled in time slots 10 minutes shorter than RO-led (60 vs 70). APRT-led Gated cases could be scheduled in time slots 15 minutes shorter than RO-led (85 vs 100).

Both APRT and RO led schedules allowed 4 Non-Gated or 3 Gated adaptive cases to be treated in first half of the day. Each APRT-led schedule allowed for 3 additional non-adaptive cases per day, compared to the RO-led schedules (23 vs 20 for Non-Gated and 24 vs. 21 for Gated).

Over a calendar year, approximately 750 additional non-adaptive treatment time slots could be scheduled using APRT-led adaptive time slots compared to RO-led with the same number of adaptive treatments, which holds if adapted cases are mostly Gated or Non-Gated.

Conclusion: Utilizing clinical timing data to determine adaptive treatment time slots suggests that shorter time slots can be used when an APRT is present, resulting in increased machine availability for non-adaptive cases.

Table 1: 90^th percentile for total treatment time and scheduled time slots in minutes utilized for hypothetical machine schedule.

	APRT-led		RO-led
	90th Percentile	Scheduled Time Slot	90th Percentile	Scheduled Time Slot
Non-Gated	59.0	60	68.6	70
Gated	84.1	85	98.2	100