Retrospective Analysis to Define Appropriate Physics FTE Support for Online Adaptive Radiotherapy Programs

Abstract

<h3>Purpose/Objective(s)</h3> In 2019, ASTRO published an update to "Safety is No Accident", a comprehensive reference guide to promote safety in radiation oncology. Included in this report are staffing guidelines that provides a simple way to calculate physics and dosimetry staffing for individual centers. Since this publication, the use of online adaptive radiotherapy (ART) has been on the rise with RT delivery units (CT- and MR-based) being cleared for clinical use. While some centers have adopted the use of online ART delivery systems, it remains unclear how to properly define the staffing of full-time equivalent (FTE) employees for an ART program. Current staffing models rely on physics to lead the delivery of adaptive sessions, including contouring and plan evaluation/selection. Our hypothesis here is that ART programs are more demanding (in terms of physics FTE) than SRS/SBRT programs. <h3>Materials/Methods</h3> In-house software was developed to query treatment delivery logs from our institution's treatment delivery system. The system's daily machine logs contain detailed information for individual patient's treatment session including time-stamps for each step in the ART treatment delivery workflow. For this study, we identify time points for the following steps in the adaptive workflow: 1) patient session is started (when patient's identity is verified prior to treatment set up), 2) start of auto-contouring review (after acquisition of CBCT), 3) completion of contour review/editing (this marks the start of dose optimization/calculation), 4) start of treatment delivery, and 5) patient session is completed (required prior to removing patient from Linac). We use methodology by Batista et al to estimate per patient relative FTE factors for physicists using treatment session times. <h3>Results</h3> Machine logs from August 2021 to February 2022 were analyzed for this study. During this time, our clinic delivered over 450 online daily adaptive treatments for 26 unique patients. Treatment sites included prostate, GYN, lungs, breast, H&N, and abdomen. On average (± std. dev.), adaptive sessions took 37 ± 16 mins from start to end. Average contour review/edit time was 7.8 ± 5.5 mins. After contour approval, it took an average of 10.1 ± 3.4 mins for plan generation, evaluation, and selection to start of treatment delivery. Based on overall session times, we calculate a conservative estimate of relative FTE factor of 0.02 for physicists per number of adaptive cases per year (w/ 30 fx/pt, 45 min/session, and 2000 work-hours/yr ≈ 0.012 + 0.008 from [1] for IGRT-based planning/QA). <h3>Conclusion</h3> The clinical adoption of online ART will increase demand for physics support. To our knowledge, this is the first data-driven analysis to make recommendations of physics staffing for CBCT-based online ART programs. The relative FTE factor measured in this study should be confirmed using multi-center data.