General comments
Definition of effective dose
In Publication 103, ICRP states that the Commission now uses reference computational phantoms of the adult Reference Male and adult Reference Female for the calculation of equivalent dose for organs and tissues. Equivalent dose can essentially be calculated only for adult reference phantom, as is the case for effective dose. On the other hand, ICRP provides the age group dependent dose coefficients for effective dose, and effective dose is used in diagnostic reference levels for various ages. Such age or sex-dependent effective dose might be misleading, so ICRP needs to explicitly describe the proper use of effective dose in practical cases, e.g. compliance with regulation, or during the optimization process in the planned exposure situation.
Organ absorbed dose
The summary of the October 2012 Main Commission meeting states “the use of the special name sievert without proper context can cause confusion, and therefore recommends that the quantity (effective dose or equivalent dose) always be specified. Furthermore, when used for equivalent dose the relevant organ must also be specified”. This statement may be explicitly described in this report, i.e., noting that “when used for absorbed dose the relevant organ must also be specified”.
Absorbed dose limits for tissue reactions
Radiation weighting for absorbed dose limits was not dealt with. Publication 118 did not provide updated knowledge on high-LET radiation. As such, developments in the relevant knowledge made since Publications 41 and 92 needs to be reviewed, and then a strategy for radiation weighting for tissue reactions needs to be discussed. For skin and extremities, wR can be used for absorbed dose limits for skin and extremities, because RBEM and RBEm have been compared. However, for the lens of the eye, such comparison has not been made, and RBE will thus be more appropriate.
Specific comments
Main Points and Paragraph 63 “This procedure introduces an element of conservatism for long-lived radionuclides with long biological half-times”
To avoid being overly conservative in assessing committed dose due to long-lived radionuclides, ICRP should encourage a quantitative evaluation of conservativeness.
Main Points and Paragraph 126 “its use exceptionally in emergency exposure situations at acute doses in the range up to around 1 Sv (or the order of several 100 mSv) is reasonable”
For managing short term exposure of the Fukushima emergency workers (age >40 with low risk for radiogenic thyroid cancer), the equivalent dose to the thyroid was added to effective dose (in the same way as for the planned exposure situation). There is the possibility that this impeded emergency responses or led emergency workers to increase their anxiety. As such, for management of dose to emergency workers, other index may be considered, taking into account mortality, lethality or severity of health effects.
Paragraph 64
Dose coefficient for internal exposure due to radiopharmaceuticals has been provided for age groups, but the control of public or occupational exposures does not include medical exposure. This statement may need to be added.
Lines 1522-1524 (Paragraph 88) “It is important to balance the reduction in doses with any deleterious effects of the action and a cautious assessment of doses could lead to unnecessary actions with adverse consequences for the affected population.”
For optimization purposes, a balance between the degree of caution and efforts for dose reduction is important in any exposure situations. To clarify this, the following revision of the sentences is proposed.
“It is important to balance the reduction in doses with any effort or resource to reduce dose in any exposure situation. Particularly in an emergency exposure situation, a too cautious assessment of doses could lead to unnecessary actions with adverse consequences for the affected population.”
Table 5.2
It needs to be explicitly stated that this table is only dedicated to risk communications for medical exposures of adults.
From the viewpoint of risk communications, it is important to touch on epidemiological observability as was done in Table 1 of Publication 96.
In the second column from the left, it needs to be stated that risk at <0.1, 0.1-1, 1-10 mSv is also based on LNT in addition to that at 10-100 mSv.
The label for the second column from the right may be changed from “Proposed term for dose level” to “Proposed term for dose level in medical exposure of adults”.
Lines 327-328 (Paragraph 3) “low dose rates (< 5 mGy/h low-LET radiation)”
The need to define the concrete level of low dose rate is unclear, and it may be better if only the order of magnitude is described while describing the relevant numbers: e.g., <5 mGy/h [originally defined by Wakeford & Tawn (PMID: 20234068) and employed by NCRP], <6 mGy/h averaged over a few hours (defined by UNSCEAR 1993), and 0.1 mGy/min averaged over one hour (UNSCEAR 2012).
Lines 368-370 (Paragraph 6) “The use of equivalent dose in setting limits for the avoidance of tissue reactions in the cases of irradiation of the hands and feet, lens of the eye, and skin; that is, limits set below thresholds for the occurrence of acute damage to organs and tissues.”
“acute” needs to be deleted. Take cataracts and circulatory effects for instance: these thresholds are set for effects occurring at >20 years and >10 years after exposure, respectively.
Lines 370-372 (Paragraph 6) “In general, smaller differences in effects per Gy are observed between radiation types in relation to tissue reactions than stochastic effects (ICRP, 2003b).”
This does not apply to the lens because the lens does not develop tumors.
Paragraph 97
Dose conversion coefficient for effective dose due to external exposure and dose coefficient for committed effective dose due to internal exposure should distinctively be described.
Lines 440-443 (Paragraph 10) “However, the available data indicate that differences between radiation types (e.g. alpha particles and neutrons relative to gamma rays) in their effectiveness per Gy in causing tissue reactions are smaller than differences in their effectiveness in relation to cancer induction (ICRP, 1990, 2003b).”
This does not apply to the lens of the eye, because the lens does not develop tumors.
Lines 1853-1854 (Paragraph 116) “Depending on the risk projection models used, there are also differences between populations.”
Risk can differ among populations, but population transfer is used for simplification.
Lines 1970-1973 (Paragraph 122) “This change to the use of absorbed dose rather than equivalent dose would not require changes to the numerical values of dose limits for tissue reactions and will be considered by the Commission when new general recommendations are formulated.”
It is unclear what the Commission will consider upon formulation of the new general recommendations.
Lines 1997-2000 (Paragraph 125) “It has been argued that this approach does not adequately protect women and younger children and that differences between males and females and greater risks at younger ages should be reflected more explicitly in the ICRP system, including the use of different detriment values and wT values.”
Detriment is used only for deriving wT. As such, age-, sex-dependent detriments have no specific functions in the system of radiological protection as indicated in Table A.4.18 of Publication 103.
Lines 2028-2033 (Paragraph 126) “A secondary consideration is that for doses in excess of 100 mSv (or more precisely, absorbed doses to organs and tissues > 100 mGy) delivered at high dose rate, the DDREF of 2 applied in determining solid cancer risk at low doses will not apply, so that risks may be somewhat greater than might be assumed on the basis of Publication 103 (ICRP, 2007a) nominal risk coefficients.”
The risk posed by acute exposure to >100 mSv can directly be estimated based on epidemiological evidence, rather than with the nominal risk coefficients.
Editorial suggestions
Lines 687-688 (Paragraph 21) “Risk of Exposure-Induced InCidence (REIC)”
“Risk of Exposure-Induced InCidence (REIC)” may be changed to “risk of exposure-induced cancer”.
Line 841 (Paragraph 34) “clinical radiology”
“clinical radiology” may be changed to “radiology, radiation oncology”.
Fig 3.2 “reference phantoms”
“reference phantoms” in the title may be changed to “adult reference phantoms”.
Lines 1085-1087 (Paragraph 54) “The standard approach to the calculation of skin doses is to determine the average dose to the most exposed 1 cm2 at a depth of 70 μm (ICRP, 1991a, 2007a)”
The local skin dose is defined by the mean equivalent dose in 0.07 mm depth averaged over any 1 cm2 of the skin, regardless of the area exposed.
Lines 1143-1147 (Paragraph 58) “the increased importance of the lens of the eye with the reduction in the dose limit to 20 mSv per year (ICRP, 2012a) has led to a re-evaluation of its application (ICRP, 2010a; Bolch et al., 2015).”
“20 mSv per year” may be changed to “20 mSv/year year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv”.