ORGAN AND EFFECTIVE DOSE COEFFICIENTS FOR CRANIAL AND CAUDAL IRRADIATION GEOMETRIES: NEUTRONS.

K G Veinot,N E Hertel,M M Hiller,K F Eckerman

doi:10.1093/rpd/ncy110

Abstract

With the introduction of new recommendations of the International Commission on Radiological Protection (ICRP) in Publication 103, the methodology for determining the protection quantity, effective dose, has been modified. The modifications include changes to the defined organs and tissues, the associated tissue weighting factors, radiation weighting factors and the introduction of reference sex-specific computational phantoms. Computations of equivalent doses in organs and tissues are now performed in both the male and female phantoms and the sex-averaged values used to determine the effective dose. Dose coefficients based on the ICRP 103 recommendations were reported in ICRP Publication 116, the revision of ICRP Publication 74 and ICRU Publication 57. The coefficients were determined for the following irradiation geometries: anterior-posterior (AP), posterior-anterior (PA), right and left lateral (RLAT and LLAT), rotational (ROT) and isotropic (ISO). In this work, the methodology of ICRP Publication 116 was used to compute dose coefficients for photon irradiation of the body with parallel beams directed upward from below the feet (caudal) and directed downward from above the head (cranial). These geometries may be encountered in the workplace from personnel standing on contaminated surfaces or volumes and from overhead sources. Calculations of organ and tissue kerma and absorbed doses for caudal and cranial exposures to photons ranging in energy from 10 keV to 10 GeV have been performed using the MCNP6.1 radiation transport code and the adult reference phantoms of ICRP Publication 110. As with calculations reported in ICRP 116, the effects of charged-particle transport are evident when compared with values obtained by using the kerma approximation. At lower energies the effective dose per particle fluence for cranial and caudal exposures is less than AP orientations while above ∼30 MeV the cranial and caudal values are greater.

Highlights

The International Commission on Radiological Protection (ICRP) Publication 103 [1] established a revised method for determining the protection quantities for organs and tissues and the effective dose
Changes to the defined organs and tissues, their associated tissue weighting factors, radiation weighting factors, and the use of sex-specific phantoms from ICRP 110 [2] required a recomputation of dose coefficients
In ICRP 103 methodology, the organ and tissue absorbed dose coefficients are determined for the male and female reference voxel phantoms separately, the appropriate radiation weighting factor applied, the sex-averaged equivalent dose coefficients obtained by averaging the values from the male and female phantoms

Summary

INTRODUCTION

The International Commission on Radiological Protection (ICRP) Publication 103 [1] established a revised method for determining the protection quantities for organs and tissues (equivalent doses) and the effective dose. Changes to the defined organs and tissues, their associated tissue weighting factors, radiation weighting factors, and the use of sex-specific phantoms from ICRP 110 [2] required a recomputation of dose coefficients. The ICRP DOCAL task group reported these dose coefficients in ICRP Publication 116 [3] which replaces ICRP 74 [4] and the International Commission on Radiation Units and Measurements Report 57 [5]. In ICRP 116 coefficients for the six standard irradiation geometries (anteriorposterior (AP), posterior-anterior (PA), right and left lateral (RLAT and LLAT), rotational (ROT), and isotropic (ISO)) are provided

Protection Quantity Calculations

Reference Phantoms

Reference Radiation Field Orientations

Calculational Method

RESULTS AND DISCUSSION

CONCLUSION