Author: Peter Jermain, Ying Niu, Abdul Rashid, Yuan Yuan, Mohammad Zarenia 👨🔬
Affiliation: Medstar Georgetown University Hospital, MedStar Georgetown University Hospital, Department of Radiation Medicine, MedStar Georgetown University Hospital 🌍
Purpose: ZAP-X is a self-shielded radiosurgery system that utilizes a linac-based isocentric technique and a compact gyroscopic gantry design. While it provides a large solid angle for beam orientation, its accessibility is limited by the constrained inner space. This study examines the dosimetric advantages of improved solid angle accessibility, made possible by the recently upgraded treatment table.
Methods: Fifteen treatment plans delivered using the ZAP-X system with the previous treatment table, where solid angle accessibility was compromised, were selected. The origin of the new treatment table, along with a corresponding generic patient model for clearance calculations, was applied to the CT images of these plans. Comparative plans were generated using the same number and locations of isocenters, identical clinical goals for target and critical organs, and consistent optimization constraints. Dosimetric comparisons were performed by evaluating the conformity index (CI), homogeneity index (HI), and gradient index (GI). Delivery efficiency was assessed by analyzing monitor units (MU) and delivery time.
Results: Compared to the original plans, the plans incorporating the upgraded treatment table demonstrated improved accessibility in solid angles, with a median increase of 22.0% (range: 8.6%–27.9%) within current mechanical limits. Exceptional and moderate plan-quality improvements were observed in 4 and 7 out of 15 plans, respectively, benefiting from newly accessible beam directions. The median reductions in CI, HI and GI were 2.7% (range: 0.8%–11.7%), 1.4% (range: 0%–4.7%), and 1.8% (range: -3.4%–13.0%), respectively. The plans utilizing the upgraded treatment table led to an average increase of 12.2% in the number of used beams, with corresponding average increases in MU and delivery time of 1.5% and 5.7%, respectively.
Conclusion: The upgraded treatment table of the ZAP-X system significantly improves solid-angle accessibility, resulting in notable enhancements in plan quality with minimal impact on delivery efficiency.