Author: Michael Evan Chaga, Timothy Chen, Darra M. Conti, Shabbar Danish, Jing Feng, Wenzheng Feng, Joseph Hanley, Tingyu Wang 👨🔬
Affiliation: Hackensack Meridian Health, Jersey Shore University Medical Center 🌍
Purpose: In August 2024, ZAP-X introduced automatic placement for isocenters in a DP-1010 upgrade for treatment planning. In this study, plans made by automatic placed isocenters are compared to those made by traditional manually placed isocenters.
Methods: Four acoustic neuroma patients are selected for this study. New plans using automatic placement of isocenters are created under the same number of isocenters used in their respective manual plans. All plans are optimized under the same constraints to reach over 99.5% coverage on the target for 18 Gy in 3 fractions. The plans are compared with each other for coverage, conformity index (CI) and gradient index (GI) on each target, and for dose constraints on organs-at-risks (OARs) as recommended by Timmerman 2021. The differences are evaluated under one-tailed paired t-test to show possible statistical significance (P<0.05).
Results: Overall, there is no statistical significant differences (P = 0.13) in target coverage and OAR doses between plans made with two methods. On average, for the plans made using automatic placement of isocenters, the target coverage increases by 0.02%, global maximum dose decreases by 94 cGy, CI increases 0.02 and GI decreases 0.26. The ipsilateral cochlea dose increases by 55.2 cGy, whereas the contralateral cochlea dose decreases by 9.13 cGy. The maximum dose in brainstem increases by 1.21 Gy. It is observed that automatic placement typically chooses more big collimators to fit to the target shape and may overlook the location of OARs nearby. The treatment time is shorter in all four patients’ cases, and on an average decreasing the time by 2.25 minutes.
Conclusion: Plans made by automatic placement of isocenters can reduce patient treatment time while keeping dosimetrically equivalent. However, manual modification may be needed for sparing OARs near targets to meet clinical objectives.