142 EPR/alanine dosimetry: Just another dose measuring system?

Electron paramagnetic resonance (EPR) dosimetry is based on a non-destructive quantitative measurement of stable free radicals in samples, induced by energy deposited by radiation. The amino acid L- α alanine shows favorable dosimetric properties: a linear response with dose, no energy nor dose rate dependence and no fading. The detector itself is small in size and tissue equivalent, which makes it an ideal measuring device for radiotherapy. Commercial available alanine dosimeters together with a low budget desktop spectrometer (Bruker EMS 104) are tested since more than two years at our department as an in vivo dose measuring system. All types of dosimeters show a perfect linear dose-response, but the background level (zero dose signal) can differ significantly between different manufacturers: from 2.5 Gy to 14 Gy. Measurement precision is less than 1% (1 σ ) if dose exceeds 10 Gy. No fading was observed over a period of one year. The reliability of alanine dosimetry for in vivo dosimetry will be illustrated with several case studies: dose measurements at the cervix wall during treatment of the cervix carcinoma with high and low dose rate brachytherapy, dose to the rectum wall; entry dose measurements during teletherapy. For all these very different cases correspondence of calculated and measured dose was excellent. From our experience we believe that alanine dosimetry can play an important role in clinical dosimetry in the future, combining advantages from TLD and diode dosimetry systems.