ESTRO 2024 - Abstract Book

S4223

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

three 3D patient-measured prostate motion traces from a previous international comparison study 5 was used. Traces included (a) continuous drift (b) high frequency and (c) erratic prostate motion. 5 For each motion trace, the plan was delivered using the KIM system and the ExacTrac system (Fig. 1). The KIM system imaged and monitored the tumour motion at 5.5 Hz during treatment, whereas, the ExacTrac system imaged and monitored the target motion only at cardinal angles. During plan delivery, a trigger condition was set both in the KIM and ExacTrac system so that any motion above 2 mm will trigger MV beam off and produce a couch shift to compensate for the detected motion. If the magnitude of the detected motion was greater than 5 mm, another pair of kV images were taken by the ExacTrac system and a single kV fluoroscopic image was acquired by the KIM system to confirm the couch shift. The geometric accuracy and precision were quantified by the mean and standard deviation of the difference between the intrafraction monitoring system measured motion with the ground truth robot motion.

Results:

Averaged over all of the traces, the geometric accuracy and precision of the KIM system was 0.0±0.6 mm, -0.2±0.6 mm and 0.1±0.9 mm in the LR, SI and AP directions respectively. The geometric accuracy and precision of the ExacTrac system was -0.3±0.4 mm, -0.2±0.9 mm and 0.3±1.9 mm in the LR, SI and AP directions respectively. As the ExacTrac system only measured the target motion at cardinal angles, all the intrafraction motion during treatment delivery were not detected by this system (Fig. 2). KIM, on the other hand, detected, and corrected any motion outside the 2 mm tolerance. With KIM monitoring, the prostate motion during MV beam on was always within the 2 mm tolerance for all three motion traces. With ExacTrac monitoring, the motion outside the 2 mm tolerance occurred 0%, 12% and 17% of MV beam-on time for continuous, high frequency and erratic traces, respectively (Fig. 2).