An experimental investigation of the electron energy dependence of the EPR alanine dosimetry system

The dose-to-water response of the EPR alanine dosimetry system for various electron beams used in radiotherapy is studied. The EPR alanine dosimetry system is established for high-dose dosimetry, usually transfer dosimetry of 60Co γ-rays. However, for clinical applications, where radiation qualities other than 60Co γ-rays are used, the behavior of the alanine dosimeter response needs to be further investigated. In the present work, electron beams from a clinical linear accelerator of the type Varian Clinac 2100 were used. Alanine dosimeters were irradiated with doses between 16 and 54 Gy in a plastic sleeve at the depths of dose maximum in a water phantom with electron beams of nominal energies of 6, 9, 12, 16 and 20 MeV (corresponding beam quality indices R50: 2.4, 3.4, 4.8, 6.5 and 8.2cm2/g). For the electron beams, the dose-to-water was monitored using a plane-parallel ion chamber, while for the 60Co γ-rays, the dose was monitored using a cylindrical chamber that was calibrated with water calorimetry. The obtained alanine dose-to-water responses for electrons relative to 60Co γ-rays indicated a small deviation from unity. An average relative response of about 0.97 for the electron beam qualities is indicated from the data. Possible explanations for the small observed response reduction relative to 60Co γ-rays are discussed.