title: Comparison of measured and Monte Carlo calculated dose distributions in inhomogeneous phantoms in clinical electron beams.
abstract: Calculations of dose distributions in heterogeneous phantoms in clinical electron beams, carried out using the fast voxel Monte Carlo (MC) system XVMC and the conventional MC code EGSnrc, were compared with measurements. Irradiations were performed using the 9 MeV and 15 MeV beams from a Varian Clinac-18 accelerator with a 10 x 10 cm2 applicator and an SSD of 100 cm. Depth doses were measured with thermoluminescent dosimetry techniques (TLD 700) in phantoms consisting of slabs of Solid Water (SW) and bone and slabs of SW and lung tissue-equivalent materials. Lateral profiles in water were measured using an electron diode at different depths behind one and two immersed aluminium rods. The accelerator was modelled using the EGS4/BEAM system and optimized phase-space files were used as input to the EGSnrc and the XVMC calculations. Also, for the XVMC, an experiment-based beam model was used. All measurements were corrected by the EGSnrc-calculated stopping power ratios. Overall, there is excellent agreement between the corrected experimental and the two MC dose distributions. Small remaining discrepancies may be due to the non-equivalence between physical and simulated tissue-equivalent materials and to detector fluence perturbation effect correction factors that were calculated for the 9 MeV beam at selected depths in the heterogeneous phantoms.
authors.affiliation: Medical Physics Unit, McGill University, Montreal General Hospital, 1650 Ave Cedar, Montreal H3G 1A4, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Doucet
authors.forename: M
authors.initials: M
authors.lastname: Olivares
authors.forename: F
authors.initials: F
authors.lastname: DeBlois
authors.forename: E B
authors.initials: EB
authors.lastname: Podgorsak
authors.forename: I
authors.initials: I
authors.lastname: Kawrakow
authors.forename: J
authors.initials: J
authors.lastname: Seuntjens
mesh_terms: D000465:Algorithms; D004583:Electrons; D008954:Models, Biological; D015233:Models, Statistical; D009010:Monte Carlo Method; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013819:Thermoluminescent Dosimetry / Q000379:methods