Exhibit Hall | Forum 4
Purpose: The goal is to evaluate the difference in terms of absorbed dose to water for a CyberKnife M6 unit resulting from the application of AAPM’s TG-51 protocol for clinical reference dosimetry and IAEA’s TRS-483 code of practice for small field dosimetry. This study also aims at evaluating beam quality and volume averaging correction factors for the CyberKnife M6 and the Exradin A12 ionization chamber using full Monte Carlo simulations.
Methods: Measurements are performed using a calibrated A12 ion chamber on a CyberKnife M6 unit and both protocols are applied. Monte Carlo simulations are performed with the EGSnrc suite using a fully modeled A12 ion chamber and an optimized CyberKnife M6 beam model to estimate quality correction factors prescribed by the TRS-483 (k(Qmsr,Q0)ᶠᵐˢʳᶠʳᵉᶠ, k(Qref,Q0)ᶠʳᵉᶠ, k(Qmsr,Q)ᶠᵐˢʳᶠʳᵉᶠ) and volume averaging correction factors.
Results: When using an in-house volume averaging correction factor, a difference in terms of absorbed dose to water per monitor unit of 0.11% is observed when applying both protocols. This difference is solely associated to the beam quality correction factor and is not statistically significant according to TRS-483’s reported uncertainties. No major difference in workload between both protocols is observed, which is consistent with the fact that IAEA’s TRS-483 formalism reduces to AAPM’s TG-51 formalism if conventional reference conditions can be established. The calculated beam quality correction factor k(Qmsr,Q0)ᶠᵐˢʳᶠʳᵉᶠ = 1.0004 ± 0.0002 differs by 0.36% from the value recommended by IAEA’s TRS-483 (1.004 ± 0.010) and is in agreement with the value estimated by Francescon et al 2019 (1.0000 ± 0.0016).
Conclusion: For clinical reference dosimetry of the CyberKnife M6, the application of IAEA’s TRS-483 is found to be consistent with AAPM’S TG-51, while differences in terms of workload are found insignificant.
Funding Support, Disclosures, and Conflict of Interest: The authors gratefully acknowledge the Natural Sciences and Engineering Research Council of Canada for financial support (NSERC CRDPJ/502332-2016). This research was enabled in part by support provided by Calcul Québec (www.calculquebec.ca) and Compute Canada (www.computecanada.ca).