ESTRO 2024 - Abstract Book

S3398

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Material/Methods:

This study uses a GK ICON treatment delivery machine, and a motion phantom custom-made to attach to the machine's mask adapter and move in one-dimensional superior-inferior motion. Phantom positioning accuracy and precision are first verified through comparisons against couch motion and computed doses. For dynamic treatment experiments, the phantom is moved through a program that first reads the desired treatment plan isocentre details, including position, time, and collimator sizes, then carries out the motion continuously while the treatment machine delivers radiation. Measurements are done with increasing levels of complexity: varying speed, varying collimator sizes, varying both speed and collimator sizes, and finally extending the same measurements to simulated 2D motion by combining phantom and couch motion. Dose comparison between phantom motion measurements and either couch motion measurements or dose calculations are analysed with 2 mm/2% and 1 mm/2% gamma indices, both using local and global gamma index calculations.

Results:

Phantom positional experiments show a high accuracy, with global gamma indices for all dose comparisons >=99%. Discretisation level to approximate continuous path as discrete points show the good dose matches with dose calculations when using 1 and 2 mm gaps. Complex 1D motion, including varying speed, collimator sizes, or both, as well as 2D motion with the same complexities, all show good dose matches with dose calculations: the scores are >=92.0% for the strictest 1 mm/2% local gamma index calculation, >=99.8% for 2 mm/2% local gamma index, and >=97.0% for all global gamma indices. Five simulated 2D treatments with optimised plans scored highly as well, with all gamma index scores >=95.3% when compared to stationary treatment, and scores >=97.9% when compared to plan calculated dose.

Conclusion:

Dynamic treatment computational studies are validated, with dynamic treatment shown to be physically feasible and deliverable with high accuracy. A 2 mm discretisation level in treatment planning is proposed as the best option for shorter dose calculation times while maintaining dose accuracy. Our experimental method enables dynamic treatment measurements using the existing clinical workflow, which may be replicated in other centres, and future studies may include 2D or 3D motion experiments, or planning studies to further quantify potential indication-specific benefits.

Keywords: Gamma Knife, Dynamic treatment, Radiosurgery

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Digital Poster

Comparison of two methods simulating inter-track interactions in the Monte Carlo toolkit TOPAS-nBio

Larissa Derksen 1 , Sebastian Adeberg 2,3 , Klemens Zink 1,2,3 , Kilian-Simon Baumann 1,2,3