Related Experiment Videos
Monte Carlo calculation of depth doses for small field of CyberKnife
Tokihiro Yamamoto1, Teruki Teshima, Satoshi Miyajima
1Department of Medical Engineering, Osaka University Graduate School of Medicine, Suita, Japan.
Purpose:
A Monte Carlo (MC) model of CyberKnife was developed as a quality assurance tool. The percentage depth dose (%dd) was verified by using this model.
Materials And Methods:
An MC model was developed with Electron Gamma Shower version 4 (EGS4) in two steps: (1) a model of the CyberKnife treatment head and (2) a model of the collimator and phantom. The bremsstrahlung spectrum was calculated using the first model, and this spectrum was then used to calculate %dds with the second model. The calculated %dds for a large field (60 mm diameter) and three small fields (30, 15, and 5 mm diameter) were compared with those measured with a diamond detector.
Results And Discussion:
The MC-calculated and measured %dd-curves for the 60 mm diameter field were in excellent agreement (<1.85%), thus confirming the validity of the model. Discrepancies between the calculated and measured %dd-curves increased with decreasing field size, with considerable discrepancy (11.62%) for the 5 mm diameter field due to lateral electron disequilibrium. Accurate dose can be determined with MC even in small fields.
Conclusion:
The MC technique can provide reliable standard data for accurate dose delivery with high-technology radiotherapies using small beams.