What is DDCC?

DDCC represents "Databases of dose conversion coefficient". These databases contain the numerical values of the fluence-to-dose conversion coefficients calculated by the PHITS code [1] coupled to the ICRP/ICRU adult reference computational phantoms [2]. The details of the calculation procedures are described in our publications [3-4]. In addition, the databases have a function to make a plot of the data for 4 user-specified conditions. These databases are useful in the shielding design of nuclear facilities and accelerators as well as the evaluation of cosmic-ray doses for aircrews and astronauts.

Introduction

Fig.1 Voxel phantoms that represent the Reference Male and Reference Female (drawn by PHITS)

The International Commission on Radiological Protection (ICRP) released a new set of fundamental recommendations for a system of radiological protection in ICRP Publication 103 [5]. These recommendations replace the Commission' previous recommendations of 1990 (ICRP Publication 60) [6], and they are expected to be incorporated in radiation protection systems of many countries in the near future. In the new recommendation, ICRP decided to introduce sex-specific voxel phantoms to represent the Reference Male and Reference Female (ICRP/ICRU reference phantoms, see Fig. 1) for the forthcoming update of organ dose coefficients for both internal and external radiation sources.
We therefore calculated the fluence-to-dose conversion coefficients using the PHITS code[2], coupled to the ICRP/ICRU reference phantoms for external exposures of neutrons, protons, alpha particles and heavy ions . Additionally, we also calculated the conversion coefficients for the dose equivalents based on the Q(L) and Q(y) relationships defined in ICRP60 and ICRU Report 40 [7], respectively, where L and y denotes LET and lineal energy for site diameter 1micron, respectively. The Q(y)-based dose equivalent has a potential to be a key quantity in constructing a more sophisticated radiation protection system in space dosimetry, since the cosmic-rays generally produce a large number of high-energy -rays around their trajectories, and their radiation qualities cannot be uniquely determined from their LET.

Calculation Procedures

For calculating the conversion coefficients for organ doses and their dose equivalents, simulations were performed to estimate the absorbed doses and their probability densities in terms of LET and y in each organ of the ICRP/ICRU reference phantoms, using the PHITS code version 2.15. In the simulation, the phantoms were irradiated by varieties of particles over wide energy ranges in various irradiation geometries. The irradiation conditions are summarized in Table 1.
The conversion coefficients from fluence to the effective dose can be calculated from the absorbed doses per unit fluence in each organ or tissue with the radiation and tissue weighting factor defined in ICRP103. The conversion coefficients for the Q(L) and Q(y)-based effective dose equivalents were derived from the corresponding organ dose equivalents, using the tissue weighting factor defined in ICRP103. The details of the calculation procedures are described in our publications [3-4].

Table 1 Irradiation conditions

Particle	Energy	Irradiation Geometry*
Neutrons	1meV - 100GeV	ISO, AP, PA, LLAT, RLAT, ROT
Protons	1MeV - 100GeV	ISO, AP, PA, LLAT, RLAT, ROT
Alpha Particles	1MeV/n - 100GeV/n	ISO, PA, PA
Heavy Ions (Li - Ni)	1MeV/n - 100GeV/n	ISO

*ISO: isotropic, AP: anterior-to-posterior, PA: posterior-to-anterior,
LLAT: left-lateral, RLAT: right-lateral, ROT: rotation

Examples of the Calculation Results

As examples of the simulation results, the calculated conversion coefficients for the effective dose and the Q(L) and Q(y)-based effective dose equivalents for neutrons and protons for the ISO geometry are shown in Fig. 2. It is evident from the graphs that the conversion coefficients for the effective dose are moderately larger than the corresponding data for the effective dose equivalent, except for the low-energy proton irradiations. This tendency indicates the numerical compatibility of the radiation weighting factor with the Q(L) and Q(y) relationships. More detailed discussions are given in our publications [3-4].

Fig.2 Calculated conversion coefficients for the effective dose and the Q(L) and Q(y)-based effective dose equivalents for neutrons (left) and protons (right) for the ISO geometry.

Summary

DDCC contains the numerical values of the calculated dose conversion coefficients. You can obtain the databases as well as its manual from the download page. Note that these data are different from the corresponding data given in ICRP116 [8] and ICRP123 [9].