Evaluation of detector performance for bremsstrahlung measurement in total skin electron treatment

Bremsstrahlung measurement in total skin electron treatment (TSET) is challenging due to low signal at extended distances (3-5 m). The suitability of various detectors for picocoulomb measurements to both electrons and bremsstrahlung are evaluated in this study.

Multiple detectors, including a 0.6 cm³ Farmer chamber, Advanced Markus parallel-plate ionization chamber, electron diode, Edge detector, microSilicon, microDiamond, and EBT3 film were used for a 6 MeV high-dose-rate beam (2500 MU/min) TSET. Measurements were performed in solid water and a small water tank. Data were analyzed in terms of signal-to-noise ratio. For EBT3 film, appropriate scaling for exposure to electron and bremsstrahlung radiation, along with standard film-handling procedures, was applied.

Signal-to-noise performance with certain detector-electrometer combinations is critical for TSET measurement as shown for the Advanced Markus chamber and the microDiamond detector that exhibit signal saturation and not suitable in TSET. With higher signal fidelity detectors, we observed a more modest increase in bremsstrahlung dose with distance, typically ranging from 0.6 % to 2.0 %. An exponential relationship, Br = 0.67·e^{(0.0017·SSD)}, is provided to estimate the magnitude of bremsstrahlung within the limits of experimental accuracy.

The Farmer chamber, Edge detector, EFD diode, microSilicon detector, and EBT3 film are best suited for bremsstrahlung measurements. The increase in bremsstrahlung dose with distance is modest, and the proposed functional form provides a practical method for estimating its magnitude at any treatment distance.