Purpose: Bremsstrahlung component in electron beam can be a limiting factor for the treatment especially for total skin electron treatment (TSET). Measurements are challenging due to the magnitude of bremsstrahlung at 3-5 meter distances. Additionally, suitability of electrometers in pico-Coulomb readings and detectors that are sensitive enough in electron and photon beams are investigated in this study.
Methods: Multiple detectors (0.6 cm³ Farmer chamber, Markus parallel plate ion chamber, Electron diode, Edge detector, microSilicon, microDiamond and EBT3 film) were used to measure bremsstrahlung component from a Varian TrueBeam® 6MeV high-dose-rate (2500MU/min) beam. Measurements were made in solid water and in small water tank. PTW Unidose reference class electrometer was used for data collection. Analysis is made in terms of signal-to-noise ratio. For EBT film proper scaling for exposure in electron and bremsstrahlung and other film precautions were used.
Results: Previously published data on Saturn machine using Markus chamber showed that component of bremsstrahlung increases with increasing distance up to 5% (Med Phys 21:1733-1738, 1994). However, this could be due to signal-to-noise ratio of some detectors and electrometer combination. It is confirmed that Markus parallel plate and microDiamond could give erroneous results due to saturation of the signal. Our data with various detectors which provide large signal indicated that bremsstrahlung increase is relatively modest (0.6-2%) with increasing distance. EBT3 film and other detectors provided nearly identical bremsstrahlung magnitude in TSET. A fitted exponential function (Br= 0.67e^0.0017x) from mean values of measurement data is provided.
Conclusion: Care should be warranted for bremsstrahlung measurement as it is overwhelmed with poor signal with clinical electrometers. Farmer chamber, Edge, EFD, microSilicon and EBT films are best suited for TSET. The bremsstrahlung increase with distance is modest and a functional form is used to estimate the magnitude.