Monte Carlo calculated beam quality correction factors for high energy photon and electron fields

Purpose: Although several studies provide data on reference dosimetry, ionization chambers are in clinical use worldwide, for which no or only a few correction factors for beam quality are available. The aim of this study was to calculate beam quality correction factors in electron and photon fields for four cylindrical ionization chamber, i.e. CC08, CC04, Razor T Chamber and Razor T Nano Chamber (all IBA, Dosimetry, Schwarzenbruck, Germany). Method: Monte Carlo simulations were performed with the EGSnrc code system to calculate the beam quality correction factor k(Q). Therefore, a detailed Monte Carlo based model of the four ionization chambers were created to calculate the dose in the sensitive volume. Electron and photon spectra of clinical linear accelerators within the entire energy range of therapeutic linear accelerators were used as radiation source. Results: k(Q) values as a function of the beam quality specifiers TPR20,10 and R-50 were calculated for high energy photon and electron fields, respectively. The data was fitted against recommended equations for photon and electron dosimetry with a chi(2) between 6.4e-7 and 4.2e-6. Conclusion: Electron and photon beam quality correction factors k(Q) were calculated by Monte Carlo simulations for the cylindrical ionization chambers CC08, CC04, Razor (TM) Chamber and Razor (TM) Nano Chamber to provide k(Q) values for absolute dosimetry according to the TRS 398 dosimetry protocol.