|Comments on the Foundation Document from Committee 1
Committee for Planning and Public Relations, Japan Radiation Research Society
1. Dose related to tissue injury
In Chapter 3, Section 3.1.7, there is a discussion whether dose equivalent (Sv) or radiation weighted dose (Gy) should be used for the dose limits for the eye and the skin, and the use of equivalent dose is recommended. There seems, however, some confusion in the discussion.
(1) gEquivalent Doseh is recommended to be replaced with gRadiation Weighted Doseh in the draft of Recommendation 2005(S14)
(2) Equivalent dose is given by multiplying the absorbed dose with the radiation weighting factor. The radiation weighting factor is defined for the stochastic effects at low dose region; therefore, it is not reasonable to use the equivalent dose for tissue injury.
(3) Although the use of equivalent dose is recommended (Lines 1174-1175), it seems to contradict the recommendation of the Committee 2 to use RBE-weighted dose (p8 in gBasis for Dosimetric Quantities Used in Radiological Protectionh).
(4) It is very confusing to use the same name of the unit gGyh for both RBE-weighted dose and absorbed dose. A name of the unit gGy-Eqh recommended in the draft 2005 recommendations (Paragraph 94) may be appropriate for this purpose.
‚Q.@Radiation Weighting Factors
The radiation weighting factor for neutrons is fully defined as a function of energy. In contrast, single values are given to the other types of radiation such as protons and heavy ions (p39, Section 4.3). Energy dependence should be carefully discussed for the particles other than neutrons. According to the discussion in light of contribution to effective dose, more persuasive reasons for employment of single values should be given. It is clear that biological effects of heavy charged particles (incl. protons) are greatly affected by energy and charge.
‚RDChanges in the Tissue Weighting Factors (p56 Table 4.3j
The tissue weighting factor for gonad was reduced from 0.2 to 0.08; and that for breast was increased from 0.05 to 0.08. In the draft 2005 recommendations the tissue weighting factor was assigned to be 0.05 for the gonad and 0.12 for the breast. Detailed explanation should be given for the change of these important factors.
‚SDThe equation on the line 2505 should be read as follows;
DD = (Average spontaneous mutation rate/average induced mutation rata)• (the dose at which the induced mutation rate is obtained)