The energy dependence of lithium formate EPR dosimeters for clinical electron beams.
The objective of this study was to investigate the potential of using polycrystalline lithium formate for EPR (electron paramagnetic resonance) dosimetry of clinical electron beams, with the main focus on the dose-to-water energy response. Lithium formate dosimeters were irradiated using (60)Co gamma-rays and 6-20 MeV electrons in a PMMA phantom to doses in the range of 3-9 Gy. A plane-parallel ion chamber was used for water-based absolute dosimetry. In addition, the electron/photon transport was simulated using the EGSnrc Monte Carlo code. From the EPR measurements, the standard deviation of single dosimeter readings was 1.2%. The experimental energy response (the lithium formate dosimeter reading per absorbed dose to water for electrons relative to that for (60)Co gamma rays) was nearly independent of the electron energy and on average 0.99 +/- 0.03. The Monte Carlo calculated energy response was on average 0.5% higher than the experimental energy response, the difference being not significant. Simulations with water and polystyrene as irradiation media indicated that the energy response of lithium formate dosimeters was nearly independent of the phantom materials. In conclusion, lithium formate EPR dosimetry of clinical electron beams provides precise dose measurements with low dependence on the electron energy.
Department of Medical Physics, The Norwegian Radium Hospital, N-0310 Oslo, Norway. eirik.malinen@fys.uio.no
Eirik
E
Malinen
Einar
E
Waldeland
Eli Olaug
EO
Hole
Einar
E
Sagstuen
D004307:Dose-Response Relationship, Radiation; D004578:Electron Spin Resonance Spectroscopy / Q000295:instrumentation* / Q000379:methods; D004583:Electrons / Q000627:therapeutic use*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005561:Formates / Q000528:radiation effects*; D018499:Linear Energy Transfer; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D005561:Formates; C030544:formic acid