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: ZapMU is the first independent monitor unit check software freely available supporting ZAP-X. In this study, the clinical experience with ZapMU for independent second check of dose calculation in ZAP-X SRS is reported.
Methods: ZapMU software was developed with Visual Basic 6.0 utilizing modified source code from CKMU, a secondary MU check software popular for CyberKnife. ZapMU calculates with heterogeneity correction, using measured off-center ratios (OCRs), tissue-phantom ratios (TPRs), and output factors (OFs) and linearly interpolating OCRs and TPRs based on beam data files generated by the ZAP-X treatment planning system (TPS). Validation of the developed software was carried out using eight plans for each collimator size on an IROC phantom. Clinical analysis was performed for 188 SRS patient plans. Percentage difference between TPS and ZapMU was obtained for the summation of isocenter dose (Diffiso) and the summation of maximum dose (Diffmax) calculated for each beam.
Results: For phantom validation, the average Diffiso was 0% and the average Diffmax was 0.003 ± 0.004% (range: 0 – 0.01%). For clinical plans, the average Diffiso was 0% and the average Diffmax was 0.3 ± 0.3% (0 – 1.46%).
Conclusion: The results demonstrate that the average dose calculated with ZapMU software is within 2% for phantom validation and within 5% for clinical plans. ZapMU is an accurate tool that can be integrated into a ZAP-X quality assurance program in Radiation Oncology departments for independent dose verification.