Consideration of the ICRP 2006 revised tissue weighting factors on age-dependent values of the effective dose for external photons.
The effective dose recommended by the International Commission on Radiological Protection (ICRP) is the sum of organ equivalent doses weighted by corresponding tissue weighting factors, w(T). ICRP is in the process of revising its 1990 recommendations on the effective dose where new values of organs and tissue weighting factors have been proposed and published in draft form for consultation by the radiological protection community. In its 5 June 2006 draft recommendations, new organs and tissues have been introduced in the effective dose which do not exist within the 1987 Oak Ridge National Laboratory (ORNL) phantom series (e.g., salivary glands). Recently, the investigators at University of Florida have updated the series of ORNL phantoms by implementing new organ models and adopting organ-specific elemental composition and densities. In this study, the effective dose changes caused by the transition from the current recommendation of ICRP Publication 60 to the 2006 draft recommendations were investigated for external photon irradiation across the range of ICRP reference ages (newborn, 1-year, 5-year, 10-year, 15-year and adult) and for six idealized irradiation geometries: anterior-posterior (AP), posterior-anterior (PA), left-lateral (LLAT), right-lateral (RLAT), rotational (ROT) and isotropic (ISO). Organ-absorbed doses were calculated by implementing the revised ORNL phantoms in the Monte Carlo radiation transport code, MCNPX2.5, after which effective doses were calculated under the 1990 and draft 2006 evaluation schemes of the ICRP. Effective doses calculated under the 2006 draft scheme were slightly higher than estimated under ICRP Publication 60 methods for all irradiation geometries exclusive of the AP geometry where an opposite trend was observed. The effective doses of the adult phantom were more greatly affected by the change in tissue weighting factors than that seen within the paediatric members of the phantom series. Additionally, dose conversion coefficients for newly identified radiosensitive organs--salivary glands, gall bladder, heart and prostate--were reported, as well as the brain, which was originally considered in ICRP Publication 60 as a member of the remainder category of the effective dose.
Lee
Choonsik
C
Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, FL 32611, USA.
Lee
Choonik
C
Han
Eun Young
EY
Bolch
Wesley E
WE
D000293:Adolescent; D001921:Brain / Q000473:pathology; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D009010:Monte Carlo Method; D019047:Phantoms, Imaging / Q000592:standards*; D017785:Photons; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D012306:Risk