Application of the ICRP/ICRU reference computational phantoms to internal dosimetry: Calculation of specific absorbed fractions of energy for photons and electrons
Résumé
The emission of radiation from a contaminated body region is connected with the dose received by radiosensitive tissue through the specific absorbed fractions (SAFs) of emitted energy, which is therefore an essential quantity for internal dose assessment. A set of SAFs were calculated using the new adult reference computational phantoms, released by the International Commission on Radiological Protection (ICRP) together with the International Commission on Radiation Units and Measurements (ICRU). Part of these results has been recently published in ICRP Publication 110 (2009 Adult reference computational phantoms (Oxford: Elsevier)). In this paper, we mainly discuss the results and also present them in numeric form. The emission of monoenergetic photons and electrons with energies ranging from 10 keV to 10 MeV was simulated for three source organs: lungs, thyroid and liver. SAFs were calculated for four target regions in the body: lungs, colon wall, breasts and stomach wall. For quality assurance purposes, the simulations were performed simultaneously at the Helmholtz Zentrum München (HMGU, Germany) and at the Institute for Radiological Protection and Nuclear Safety (IRSN, France), using the Monte Carlo transport codes EGSnrc and MCNPX, respectively. The comparison of results shows overall agreement for photons and high-energy electrons with differences lower than 8%. Nevertheless, significant differences were found for electrons at lower energy for distant source/target organ pairs. Finally, the results for photons were compared to the SAF values derived using mathematical phantoms. Significant variations that can amount to 200% were found. The main reason for these differences is the change of geometry in the more realistic voxel body models. For electrons, no SAFs have been computed with the mathematical phantoms; instead, approximate formulae have been used by both the Medical Internal Radiation Dose committee (MIRD) and the ICRP due to the limitations imposed by the computing power available at this time. These approximations are mainly based on the assumption that electrons are absorbed locally in the source organ itself. When electron SAFs are calculated explicitly, discrepancies with this simplifying assumption are notable, especially at high energies and for neighboring organs where the differences can reach the same order of magnitude as for photon SAFs. © 2010 Institute of Physics and Engineering in Medicine.
Mots clés
Elsevier
Germany
Helmholtz
High energy
High-energy electron
Internal radiation
International Commission
International commission on radiological protections
Lower energies
Mathematical phantoms
Monoenergetic
Monte Carlo transport code
Nuclear safety
Order of magnitude
Radiation unit
Radiological protection
Simplifying assumptions
Target regions
Dosimetry
Photons
Quality assurance
Radiation protection
Radiology
Total quality management
Electrons
adult
article
biological model
breast
colon
comparative study
computer simulation
electron
female
health care quality
human
image quality
instrumentation
liver
lung
methodology
Monte Carlo method
photon
radiation dose
radiation exposure
radiometry
sexual development
stomach
thyroid gland
validation study
Adult
Breast
Colon
Computer Simulation
Female
Humans
Liver
Lung
Models
Biological
Monte Carlo Method
Phantoms
Imaging
Quality Assurance
Health Care
Radiation Dosage
Radiometry
Sex Characteristics
Stomach
Thyroid Gland
Approximate formulas
Body models
Computational phantom
Computing power
Dose assessments