Accuracy of the electron transport in mcnp5 and its suitability for ionization chamber response simulations: A comparison with the egsnrc and penelope codes

• Published in: Medical physics (Lancaster) 2012-03, Vol.39 (3), p.1335-1344
• Main Authors: Koivunoro, Hanna, Siiskonen, Teemu, Kotiluoto, Petri, Auterinen, Iiro, Hippeläinen, Eero, Savolainen, Sauli
• Format: Article
• Language: English
• Subjects: Absorption; ACCELERATORS; ACCURACY; COBALT 60; Collisional energy loss; DEPTH DOSE DISTRIBUTIONS; DOSIMETRY; Dosimetry/exposure assessment; Drug delivery; EGSNRC; electron beam effects; ELECTRON BEAMS; Electron Transport; Electronic transport; ENERGY LOSSES; Gases; ionisation chambers; IONIZATION CHAMBERS; MCNP; METHANE; MEV RANGE 01-10; Monte Carlo; MONTE CARLO METHOD; Monte Carlo methods; Multiple scattering; NEUTRON CAPTURE THERAPY; Neutrons; PENELOPE; PHANTOMS; PHOTON BEAMS; PHOTONS; RADIATION DOSES; Radiation therapy; RADIOLOGY AND NUCLEAR MEDICINE; Radiometry - instrumentation; SIMULATION; STRAGGLING; Therapeutic applications, including brachytherapy; THIN FILMS; TRANSPORT THEORY; Water
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3685446

Purpose: In this work, accuracy of themcnp5 code in the electron transport calculations and its suitability for ionization chamber (IC) response simulations in photon beams are studied in comparison to egsnrc and penelope codes. Methods: The electron transport is studied by comparing the depth dose distributions in a water phantom subdivided into thin layers using incident energies (0.05, 0.1, 1, and 10 MeV) for the broad parallel electron beams. The IC response simulations are studied in water phantom in three dosimetric gas materials (air, argon, and methane based tissue equivalent gas) for photon beams (60Co source, 6 MV linear medical accelerator, and mono-energetic 2 MeV photon source). Two optional electron transport models of mcnp5 are evaluated: the ITS-based electron energy indexing (mcnp5 ITS) and the new detailed electron energy-loss straggling logic (mcnp5 new). The electron substep length (ESTEP parameter) dependency in mcnp5 is investigated as well. Results: For the electron beam studies, large discrepancies (>3%) are observed between themcnp5 dose distributions and the reference codes at 1 MeV and lower energies. The discrepancy is especially notable for 0.1 and 0.05 MeV electron beams. The boundary crossing artifacts, which are well known for the mcnp5 ITS, are observed for the mcnp5 new only at 0.1 and 0.05 MeV beam energies. If the excessive boundary crossing is eliminated by using single scoring cells, the mcnp5 ITS provides dose distributions that agree better with the reference codes than mcnp5 new. The mcnp5 dose estimates for the gas cavity agree within 1% with the reference codes, if the mcnp5 ITS is applied or electron substep length is set adequately for the gas in the cavity using the mcnp5 new. The mcnp5 new results are found highly dependent on the chosen electron substep length and might lead up to 15% underestimation of the absorbed dose. Conclusions: Since themcnp5 electron transport calculations are not accurate at all energies and in every medium by general clinical standards, caution is needed, if mcnp5 is used with the current electron transport models for dosimetric applications.