Physical dose validation of dynamic treatment for Gamma Knife radiosurgery

• Published in: Medical physics (Lancaster) 2024-05, Vol.51 (5), p.3635-3647
• Main Authors: Tham, Benjamin Z., Aleman, Dionne M., Heaton, Robert K., Nordström, Håkan, Coolens, Catherine
• Format: Article
• Language: English
• Subjects: dose validation; dynamic treatment; Gamma Knife; Humans; Phantoms, Imaging; Radiation Dosage; Radiometry; Radiosurgery - methods; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1002/mp.17034

Background Dynamic treatment in Gamma Knife (GK) radiosurgery systems delivers radiation continuously with couch movement, as opposed to stationary step‐and‐shoot treatment where radiation is paused when moving between isocenters. Previous studies have shown the potential for dynamic GK treatment to give faster treatment times and improved dose conformity and homogeneity. However, these studies focused only on computational simulations and lack physical validation. Purpose This study aims conduct dynamic treatment dosimetric validation with physical experimental measurements. The experiments aim to (1) address assumptions made with computational studies, such as the validity of treating a continuous path as discretised points, (2) investigate uncertainties in translating computed plans to actual treatment, and (3) determine ideal treatment planning parameters, such as interval distance for the path discretization, collimator change limitations, and minimum isocenter treatment times. 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 1D superior‐inferior motion. Phantom positioning is 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 isocenters' 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, then extends the same measurements to simulated 2D motion by combining phantom and couch motion. Dose comparisons between phantom motion radiation measurements and either couch motion measurements or dose calculations are analyzed with 2 mm/2% and 1 mm/2% gamma indices, using both local and global gamma index calculations. Results Phantom positional experiments show a high accuracy, with global gamma indices for all dose comparisons ≥$\ge $99%. Discretization level to approximate continuous path as discrete points show the good dose matches with dose calculations when using 1 and 2‐mm gaps. Complex 1D motion, including varying speed, collimator sizes, or both, as well as 2D motion with the same complexities, all show good dose matches with dose calculations: the scores are ≥$\ge $92.0% for the strictest 1 mm/2% local