Dosimetric comparison of 4MeV and 6MeV electron beams for total skin irradiation

Abstract

Background In this study, dosimetric aspects of TSEI consisting of a 4MeV beam with no spoiler were investigated in comparison to a nominal 6MeV beam with spoiler, and the potential for clinical applications was evaluated.

Methods The TSEI technique is based on the Stanford technique, which utilizes a beam configuration of six-dual fields. MOSFETs were used to measure the optimal gantry angle, profile uniformity, and absolute dose at the calibration point. The depth dose curve of the central axis was measured in the treatment plane using EBT2 film. Photon contamination was measured as the dose at 5cm depth in a solid water phantom relative to the maximum dose using a parallel plate ion chamber. A MOSFET dosimeter placed on the surface of a humanoid phantom, and EBT2 films inserted into a humanoid phantom were used to verify the TSEI commissioning.

Results Dosimetric aspects of the 4MeV TSEI beam, such as profile uniformity (±10%) and relative photon contamination (<0.001%), were comparable to those of a 6MeV TSEI beam. The relative depth dose of the 4MeV electrons was 81.4% at the surface and 100% at 0.4cm. For the 6MeV electrons, the relative depth dose was 93.4% at the surface and 100% from 0.2cm to 0.4cm. The calculated B-factor of the 4MeV TSEI beam was 1.55, and 1.53 for the 6MeV TSEI. 80% of the prescribed dose was obtained at 0.22cm depth for the 4MeV TSEI beam and 0.53cm for the 6MeV TSEI beam in the humanoid phantom measurement.

Conclusions The suggested 4MeV beam for TSEI could be applied to shallow depth skin diseases and to electron boost as second treatment course.