ESTRO 2024 - Abstract Book

S4315

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

ESTRO 2024

The effective dose resulting from the IFCBCT and SeedTracker-based monitoring approaches for a dual arc VMAT plan with 6MV photons was estimated for prostate hypofractionation (60Gy/20 fractions) and SBRT treatment (40Gy/5 fractions) using PCXMC software. The image acquisition parameters used for both imaging approaches are presented in Table 2. To optimize the minimum imaging frequency, which can be controlled as a function of gantry angle spacing in the XVI system, for SeedTracker monitoring, the control points' delivery time of 20 retrospective prostate hypofractionation and SBRT plans were calculated. Based on this information, we determined the plan and arc specific imaging frequency and the resulting dose for position tolerances of 3mm over two durations: 1 second (3mm/1s) and 5 seconds (3mm/5s).

Table2: Image acquisition parameters.

Results:

Static offsets introduced at the start of the treatment arc were detected by IFCBCT, and the calculated offsets were consistently within 0.5mm in any direction. In scenarios where static offsets were introduced at 25%, 50%, and 75% of the treatment arc, the duplication of seeds was observed in the IFCBCT image set. Seed auto-registration resulted in a calculated position offset difference of a maximum of 5mm compared to the introduced offsets. After aligning the seeds from the plan data with the second set of duplicated seeds in IFCBCT, the maximum difference reduced to 1mm compared to the introduced offsets.

Continuous drift introduced blurring of seeds in the IFCBCT image set. Auto seed registration resulted in a maximum difference of 0.4mm compared to the final position of the phantom at the end of the treatment arc. In cases of erratic