Author: Michael Evan Chaga, Timothy Chen, Shabbar Danish, Jesse Feng, Joseph Hanley, Georg A. Weidlich 👨🔬
Affiliation: Zap Surgical, Tenafly High School, Jersey Shore University Medical Center 🌍
Purpose: ZapMU is the first independent monitor unit check software freely available supporting ZAP-X. In this study, the validation of ZapMU for independent check of dose calculation is performed, utilizing measured beam data within individual institution and composite representative beam data from 10 different institutions.
Methods: ZapMU software was developed with Visual Basic 6.0 source code modified from CKMU. ZAP-X beam data includes output factors (OFs), tissue-phantom ratios (TPRs), and off-center ratios (OCRs) for each 8 cone size. A csv file including beam parameters can be exported from the ZAP-X treatment planning system (TPS). ZapMU interpolates beam data to calculate OF, TPR, OCR, source-to-surface distance and depth. Validation of the developed software was performed with 10 SRS patient plans evaluated using measured data of OCRs, TPRs, and OFs and composite representative beam data measured from 10 different institutions. Patient demographics consisted of 8 Brain Metastases, 1 Meningioma, and 1 Trigeminal Neuralgia. Plan prescriptions ranged from 16–90 Gy and prescription isodose line ranged from 51–100%. Percentage difference between TPS and ZapMU was obtained for the summation of each isocenter dose (Diffiso) calculated for each beam and the maximum point dose (Diffmax).
Results: For measured beam data validation, the Diffiso was 0.0% and the Diffmax was 0.5±0.5% (range: 0–1.09%). For composite beam data validation, the Diffiso was 2.2±1.2% (1.25–4.54%) and the Diffmax was 3.4±1.3% (1.29–6.06%).
Conclusion: The results demonstrate that the dose calculated with ZapMU software is within 5% of the TPS with measured beam data and 7% with composite beam data. Independent dose calculation with ZapMU should be used for all patient plans. Calculation with institution measured beam data can catch gross error from TPS calculation; while calculation with composite beam data can be used to validate the commissioning and measurement of institution beam data.