Abstract Background: Adaptive radiation therapy (ART) is a personalized radiation treatment approach which adjusts the treatment plan during the radiation course to account for anatomic changes and tumor response. Real-time adjustment allows for smaller margins, particularly in stereotactic partial breast irradiation (SPBI, 1). We have implemented a radiation therapy technologist (RTT) driven workflow at our institution which was previously shown reduces treatment demand on physicians without compromising plan quality (2). Here we report with more experience the adaptive stereotactic partial breast irradiation (A-SPBI) workflow is more efficient and total treatment time is quicker for patients. Objectives: Describe our institutional experience with A-SPBI and demonstrate that with increased ART experience, treatment time is quicker while maintaining plan quality and delivery compared to the inception of the ART program. Methods: We retrospectively reviewed patients with early stage breast cancer treated with A-SPBI between 01/2023-03/2025. Patients received SPBI on a cone beam computed tomography-based ART platform. Thirty Gy in 5 fractions was prescribed to the planning target volume (PTV) delivered twice weekly on non-consecutive days. A total of 867 fractions were evaluated. RTTs prospectively collected treatment planning time which was defined as time taken from the initial cone beam to time at which the plan was signed by the physician. Results: Eight hundred and sixty-seven A-SPBI fractions were evaluated from 01/2023-03/2025. From 01/2023-06/2023, ART was physician-driven where clinicians contoured in-person organs at risk (OARs) and target volumes for each fraction with an average planning time of 17.4 minutes. During this time, RTTs were present to review contours and concurrently trained for ART certification, the process for certification which has previously been described (2). From 07/2023-04/2024, RTTs contoured OARs and target volumes under direct supervision from a physicist or physician with an average planning time of 22.2 minutes. Importantly during this time, 95% of fractions had no major edits or only stylistic changes recommended by the reviewing physician. From 10/2024 - 03/2025, A-SPBI was primarily RTT-driven. RTTs generated OARs and target volumes with remote physician review with an average planning time of 19.8 minutes. From 10/2024-03/2025, this was reduced to 17.0 minutes. Comparing 03/2025 to 07/2023, RTTs have decreased treatment delivery time by 3.3 minutes per fraction (p=0.0004 welch’s t-test) while allowing physicians to review contours and plans remotely, and also doubling total number of delivered fractions. Conclusions: With 27 months of follow up and more experience, A-SPBI treatment delivery time has decreased while still maintaining plan quality with an RTT-driven workflow platform. Sources: 1. Montalvo SK, Kim N, Nwachukwu C, Alluri P, Parsons D, Lin MH, Cai B, Zhuang T, Hrycushko B, Chen L, Timmerman R, Rahimi A. On the feasibility of improved target coverage without compromising organs at risk using online adaptive stereotactic partial breast irradiation (A-SPBI). J Appl Clin Med Phys. 2023 Feb;24(2):e13813. doi: 10.1002/acm2.13813.2. Parsons D, Domal S, Chambers E, Salazar D, Visak J, Arbab M, Holgado F, Li X, Okoro C, Wandrey N, Iqbal Z, Alluri P, Cai B, Keen H, Cleaton J, Godley A, Sher D, Badiyan S, Rahimi A, Lin MH. Feasibility and Impact of a Radiation Therapy Technologist-Driven Workflow for Cone Beam Computed Tomography Guided Partial Breast Adaptive Radiation Therapy. Int J Radiat Oncol Biol Phys. 2025 Jul 15;122(4):893-901. doi: 10.1016/j.ijrobp. Citation Format: N. Wandrey, D. Parsons, J. Wang, M. Arbab, P. Alluri, X. Li, A. Rahimi. Partial Breast Adaptive Radiation Therapy Workflow Decreased Planning Time with Increased Institutional Experience abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-07-26.
Wandrey et al. (Tue,) studied this question.