ESTRO 2025 - Abstract Book

S2662

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

treatment plansremains below the doses recommended in guidelines (<2 Gy). However, further validation with a larger dataset is necessary.

Keywords: out-of-field dose, OSL dosimetry, CIED

3976

Digital Poster Dose delivery accuracy of visually gated SBRT: a stress test for clinical acceptance Arttu Cowell 1 , Pauliina Petrow 2 , Laura Tuomikoski 2 , Antti Kulmala 3 1 Department of Science, University of Oulu, Oulu, Finland. 2 Radiotherapy, Comprehensive Cancer Center, Helsinki, Finland. 3 Radiotherapy, Clinical Research Institute HUCH Ltd., Helsinki, Finland Purpose/Objective: As radiation therapy continues to advance, 4D methods are becoming increasingly relevant for achieving personalized and dynamic cancer treatment plans, marking a significant evolution in radiotherapy. Since 4D therapy relies on tracking and compensating for tumor motion over time, inaccuracies can lead to underdosing the tumor or inadvertently irradiating healthy tissues. Material/Methods: A Winston-Lutz-type (field size = (3 × 1.5) cm² and beam angles = 0°, 120°, and 240°) radiotherapy plan was measured using a dynamic thorax phantom with a moving cylindrical insert containing a target sphere (at isocentre) and dosimetric film (outside the cylinder). The Respiratory Gating for Scanners (RGSC) (Varian Medical Systems, Palo Alto, CA, USA) was used to monitor target motion and gating the radiation production. The performance of the RGSC was tested with various motions, including a 6-second period cos⁴ wave, a "cough"-type motion, a 2-second period cos⁴ wave, a trapezoid wave, and a triangle wave. To quantify the performance of RGSC, the planned dose was interpolated to the film cylinder (Figure 1) and gamma indices: Gamma Passing Rate (GPR) and ΔGPR (ΔGPR = dynamic plan GPR – static plan GPR), were calculated using the criteria: 1 mm distance-to-agreement and 2 % dose difference.