ESTRO 2025 - Abstract Book

S4405

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

Conclusion: Conclusion: AI-generated bowel bag contours demonstrated high similarity to the clinical contours, with small, clinically acceptable differences. Geometric deviations observed in the cranial region of the bladder were systematic and should thus be manageable. This study highlights the potential of unsupervised AI-generated structures enabling faster adaptive procedures, potentially minimizing the impact of intrafractional anatomical variations,

while preserving target dose coverage. Keywords: Bladder cancer, AI, oART

References: [1] Åström LM, Behrens CP, Calmels L, Sjöström D, Geertsen P, Mouritsen LS, Serup-Hansen E, Lindberg H, Sibolt P. Online adaptive radiotherapy of urinary bladder cancer with full re-optimization to the anatomy of the day: Initial experience and dosimetric benefits. Radiother Oncol. 2022 Jun;171:37-42. doi: 10.1016/j.radonc.2022.03.014. Epub 2022 Mar 28. PMID: 35358605.

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Proffered Paper APRT Analysis for Online Adaptive Radiotherapy Contouring and Adaptor Model Evaluations Using Time Driven Activity-Based Costing Robbie Beckert 1 , Eric Laugeman 1 , Alex Price 2 , Eric Morris 1 1 Radiation Oncology, Washington University School of Medicine in St. Louis, St. Louis, USA. 2 Radiation Oncology, Case Western Reserve University, Cleveland, USA Purpose/Objective: Online adaptive radiotherapy (oART) tailors' treatment plans to daily patient anatomy changes, but delivering such care remains resource intensive. This study assessed the impact of implementing an advanced practice radiation therapist (APRT), as a physician-extender, on contouring times. Using clinical timing data, a time-driven activity based costing (TD-ABC) 1 analysis evaluated the estimated contouring cost of various adaptor models (USD $) per fraction and per year for an adaptive SBRT program. Material/Methods: A 2-year analysis of our high-volume oART SBRT program was done evaluating the effect that the APRT had on contouring times compared to physicians across a large SBRT patient cohort 2 . All timing data were stratified and compared depending on whether the individual APRT was present and contouring or if the APRT was absent and one of a team of radiation oncologists (RO) was the primary adaptor. The collective data was then used to assess the financial impact of contouring for various hypothesized adaptor models through TD-ABC using both APRT contouring times for all providers (Individual cost) and RO contouring times for all providers (Team cost). Results: Timing data was recorded for 530 adaptive SBRT fractions for 117 individual SBRT patients. The APRT was the primary adaptor for 339/530 fractions, while the RO was primary adaptor for 191/530 fractions. APRT contouring was performed by one APRT, and physician contouring was performed by a team of seven physicians. Data indicated that APRTs significantly reduced contouring times by 10 minutes on average, compared to RO fractions (p<0.001). Figure 1 shows the per fraction ranges of the TD-ABC analysis. The estimated cost was projected over our previous year (692 fractions on 139 patients) with physician contouring cost ranging between $23,224 for individual coverage to $50,855 for Team coverage. For physics, dosimetry and APRT the ranges are $12,961-28,448, $7,224 15,826, and $5,605-12,276, respectively.