|Comments on RP-05 (ICRP Recommendations 2005)
Dr. D.N.Sharma (Member RASSC), Dr. B.S.Rao, Dr. A S Pradhan , Dr. Pushparaja, Dr. R.K. Gopalakrishnan and Dr. B. Rajashekharrao
Health, Safety and Environment Group
Bhabha Atomic Research Centre, Trombay, Mumbai, India
1. ICRP may consider to add an Introduction / Editorial to demonstrate clearly the changes from the ICRP-60 and the necessity / rational for the compelling changes demanding the new Recommendations.
2. Frequent changes in Radiation Protection terminologies create problems at the operational level. The radiation protection professionals has taken time to adapt and make aware the personnel at operational level the terminologies proposed in ICRP-60. Now introduction of new terminologies such as:
¡¥Tissue reaction¡¦ in place of ¡¥Deterministic effects¡¦, ¡¥Radiation weighted dose¡¦ in place of ¡¥Equivalent dose¡¦, Proposal to introduce new unit for ¡¥Radiation weighted dose¡¦ while keeping units for ¡¥effective dos¡¦ same etc., may create confusion. We are of the view that these changes seem to be unnecessary as these are not going to bring in any fundamental changes in the recommendations.
3. Regarding the dose constraints proposed in the text there is confusion as to what these refer to? In the text it looks these and ¡¥dose limits¡¦ are overlapping. If this is true, meaning of ¡¥optimization¡¦ gets blurred.
The lowest constraint introduced i.e., 0.01 mSv is still more confusing. Dose this mean one has to apply optimization even below 0.01 mSv effective dose, which has been accepted world over as ¡¥trivial dose¡¦?
Furthermore, it may be difficult to quantify the constraints for all situations. This appears to have been overemphasized and not carried out adequately / convincingly, because the concept of constraints is already existing and duly taken care by the basic requirement of optimization and ALARA. The over emphasis overlaps with the limits and the optimization. The aim of enhancing the protection appears to have been already taken care because of the conclusion that probability coefficients for stochastic effects are reduced by more than 10% as compared to values of ICRP-60 (But this too should not generate logic in future to increase the dose limits because the prob. for the stochastic effects reduced). Therefore, it appears that the changes in the new recommendations could be minimized.
4. Removal of the concept of ¡¥Avertable Dose¡¦ during an ¡¥intervention¡¦ in an emergency situation will lead to undue consequences as it amounts to that ¡¥intervention¡¦ need not to be justified.
5. It is okay that we should protect environment and radiation protection community is alive to this. Regarding protection of non-human species, it is acceptable in principle. But can there be a common benchmark for the protection of human and non-human species? It is difficult to visualize. Furthermore, we are not sure which species we are talking about. Arguments can go as far as protecting species like earthworm. Are we going to burden the radiation safety related resources to protect species like earthworm? We are afraid this type of approach may generate an argument against ¡¥Atomic Energy¡¦ itself.
6. It seems ICRP is giving up the concept of ¡¥collective dose¡¦, which is currently being used as a safety index of an operating facility and for estimating risk to the public. We are of the view that this is an important concept and must be retained.
7.Basis of choosing Natural Background level (its fractions / multiples) for the need for action is not clear and need more clarification / justification and the basis. There may be need to include or refer the situation in high background areas when emphasis may be given to aircrew members.
8. There are several ambiguities in the terms especially while referring to volunteers, occupational workers, emergency team members, carers / comforters, public etc. and the constraints / dose limits applicable to them.
9.Significant enhancement in the tissue-weighting factor for the breast needs a clarification whether this will lead to a Gender based limits and constraints or this has been averaged, if so, how?
10. It appears that the use of ALI (where the internal exposure is of main concern) has been ignored / dropped out, but this quantity has played a significant role and may therefore be retained in a restricted way.
(Format: Comment No., Page No., Para No. in the Document)
1, 16, 40: There is no need to stress the importance of using the WR values only in the context of stochastic effects. It is well known that WR values used are based either on the radiation carcinogenesis data or other stochastic effects such as induction of cytogenetic damage in peripheral blood lymphocytes. These values are far less for the induction of cell killing, which leads to the deterministic effects (tissue reactions). Quite often RBE for cell killing does not exceed 3-4 even for the most effective radiation. The RBE must be defined for every different tissue for each end point scored (and also for the level of the effect). It would be best not to attempt to arrive at any single value. To site an example, the RBE for neutrons for the induction of cataracts can vary from 2-5 depending on the energy. It is difficult to predict tissue reactions based on WR value defined for deterministic effects.
2, 16, 42: What is meant by within a single hit cell? Suffice it to say that the distribution of damage in cells follows Poisson distribution.
3, 17, 46: "The value of energy imparted in most individual cells is then zero¡K¡K¡K."
This statement is not true even for low doses of low LET radiation.
4, 20, 58: It would be good to clearly state that the WR values must be based on the maximum RBE values. Since the dose response curve for low LET radiations are mostly linear quadratic, at very low doses and low dose rates, the response corresponds to purely linear component of damage.
5, 21, 67: In the preceding paragraphs, a number of arguments have been presented to use a single WR values for low LET radiation. But there is no doubt that the effectiveness of X-rays (lower energy) and tritium ƒÒ rays are at least 2. If the source of exposure is well known why shouldn't a WR value of 2 be used to be more precise. There is no need to look for the evidence from animal experiments when the cytogenetic end points in human peripheral blood lymphocytes clearly resolves the differences among the aforesaid low LET radiations. The ƒÑ coefficients are so distinct that the differences are difficult to ignore. Since at low-level exposures like occupational exposures, it is only the ƒÑ coefficient that matters, it may be good to use a WR value of two for HTO ƒÒ rays. The human exposure takes place frequently by the internal route. In the case of X-rays, it is true that mostly skin and underlying tissues absorb the softer components, but skin is the most frequently exposed tissue. What is the WR value to be used for assessment of breast cancer risk from mammography procedure with low energy X-rays? Is ¡¥one¡¦ an adequate value? If we can concentrate so much to compute different WR value for neutrons of different energies, we can as well do so for different low LET radiation. When we state clearly that the effectiveness of radiations varies, the effective doses based on a common WR value are erroneous.
We do see the convenience of using a single WR value for all the low LET radiations. But the arguments provided here are sketchy and not convincing. The statements even sound contradicting.
6, 22, 71: The calculations presented here suggest that nearly 20 % of the dose for 1 MeV neutrons result from low LET radiation whereas the low LET component of dose increases to >90 % in low energies.
As far as we understand the ICRP 60(1991) has addressed to all the attributes of detriment, nothing has been ignored. The only difference we see is the change over from the mortality data to incidence data. It is indeed a welcome move and of course a more reliable end point. Probably this difference has come due to the use of ICRU sphere in ICRP-60 and anthropomorphic phantom now. This needs to be clarified.
7, 27, 94: It is important to resist the temptation to define the Gy-Eq. Since the RBE values vary significantly for the same radiation under different conditions / levels of exposure and for assay of biological effect, it is practically impossible to arrive at an appropriate RBE for a particular radiation.
8, 27, 95: This statement is not entirely true. It can be modified as:
¡¥Apart from¡K control of stochastic effects will avoided the occurrence of most, and probably all, issue reactions.
9, 28, Table 4: Even though tissue necrosis occurs after some delay, it may not strictly a late effect. On the other hand, fibrosis that occurs in many tissues, contraction, atrophy, hypothermia that occur in the skin, and cataract of the lens are good examples of late effects. This table could have been more elaborate describing a number of tissue reactions.
10, 29, Table 5: This table is quite confusing. Last column shows the doses required for 1% incidence, this is misleading, 1% is not applicable to most of the end points. 1% incidence may be purely due to over sensitivity of one person out of hundred for radiation dose. It is too low an incident rate to draw such important conclusion.
When we describe the deterministic effects, it would be good either to suggest a threshold dose or 50% reaction dose. Why should temporary sterility occur in three weeks? It should take at least 6 weeks in human beings.
Why should 1 Gy radiation lead to mortality at all? If I do recall the data from a number of accidents involving a few hundred mortalities, there are no deaths for doses less than 2 Gy. At one Gy at least 37% of the bone marrow stem cells survive. I do not see the possibility of death attributable to radiation alone. The dose required for fatal pneumonitis may be well above 8 Gy, 6 Gy may be an underestimate. It is difficult to arrive at the doses required to elicit 1 % reaction due to the many uncertainties and there is no need to commit some dose values when we are quite uncertain about them.
In addition to the above, values of the absorbed doses should be greater than (>) the given value for the threshold and in no case less than (<) or a fixed value.
11, 30, 103: The follow up is for 48 y and not 47 years.
12, 31, 111: Working population has always been described in the past in the age range of 18-65 y, but here we see 20-64 y. The working age could have been harmonized.
13, 32, 117: We have carefully studied the report by Otake and Shull on the incidence of severe mental retardation among those exposed in-utero. There is not much of an evidence for a threshold, but statistically a threshold cannot be ruled out. If we recall correctly, the reduction of IQ is 30 units Sv-1. Since not much is known about the mechanism of induction of mental retardation, there is no need to stress on the threshold of 300 mGy. There is no way to prove this. If this is true there is no need to have separate limits to pregnant women.
Pregnant women may be advised to work in areas, where the effective dose doses not exceed 0.75 mSv (3/4th of public dose limit) for the next 9 months. This is easier to control exposure for occupational workers. Should this be followed for contractor¡¦s workers, who are declared as pregnant??? How? (Setting a limit of 2 mSv really does not help). Since the incidence of untoward pregnancy and malformations is significant, there is a need to protect pregnant women against radiation. Such a step will avoid unnecessary confusion and save radiation from being held responsible for many unfortunate incidences.
So far as the guidance on termination of pregnancy is concerned, it should not have any threshold and should be advised on case to case basic only.
14, 33, 123: Even though an increase in non cancer mortalities has been reported, there is no known reason as to why low doses and chronic exposures should cause such effects. It is not surprising to see this among those exposed to large doses and also among radiotherapy patients, since this is likely to be caused by severe cellular damage in the tissues. But this effect seen among those exposed to large doses should be declined with the possible increase in non-exposed population which may be manifestation of other reason like stress, lifestyle etc. Hence, these non-cancer mortalities may not be a matter of concern in occupational type exposures.
15, 48, Table 9: These dose limits are really for low LET radiations. We feel that a more serious thinking is necessary to assign meaningful WR values; otherwise these limits should be restricted to gamma rays (photons). Limit on skin is adequate to take care of tissues of hands and feet. A separate limit is not justified.
16, 70, A 30: qT has been defined here as an adjusted lethality fraction. We think it is the same as [(1-q min) q + q min ] shown in page 72. I think kT and q both refer to lethality. If that were so, it would be good to use only one of them throughout the document.
17, 44, 169: Including administrative and support staff in the ¡¥general public¡¦ category is like merging ¡¥public domain¡¦ with the site boundary. This will have additional burden on personal monitoring services and may lead in future to unnecessary complications. One should not separate out workers in un-controlled areas from those working in controlled areas within the site boundary of a nuclear facility. As we have been stating, within the dose-limit boundary, the exposures are ¡§acceptable¡¨ for accepting occupation in nuclear industry, which is considered as reasonably safe. They too are working within the acceptable level of risk for occupational workers and should not be taken as members of the public.
18, 54, 213-224: Though it is understood that dose constraints would apply to workers, however, in case of members of the public, especially family members who are providing care and support to the patient, a dose constraint applied, would be for a single diagnostic or a treatment procedure or multiple procedures needs to be clarified. There is a very good likelihood that a patient may undergo a diagnostic or treatment procedure more than once a year, for e.g. 131I treatment for hyperthyroidism or thyroid cancer. In such cases, whether the dose constraint is for a single year (if yes, how this year to be taken?) or is it for a single procedure needs to be elaborated.
In medical application of radiation, in addition to the physicians, technologists and physicists are an integral part of patient management. The commission has stressed the importance of training only of physicians but not of the other important paramedical personnel viz. technologists and physicists. More often, the physician decides and prescribes the dose in consultation with the Physicist. And technologists deliver this dose. It is vital that the emphasis of radiation protection training is extended to these personnel as well
19, 55, 225-227: In cases of individuals, consenting to help the patients by providing support and comfort to the patients, the exposure of such individuals have been considered as medical exposures. However, this will be justified only if it is a non-ambulatory or a pediatric patient. Those instances where the patient is not entirely dependent for care and support, the exposure may be non-voluntary and thus dose constraints should be considered rather than it being termed as medical exposures.
It would be necessary to consider and discuss the likely exposure to friends and family members of deceased patient containing therapeutic amounts of radioactivity. These are very rare events and therefore if at all a death event occurs, considering the sentiments of the bereaved family, there should be no restrictions on the release of the cadaver but to avoid possible public exposures during cremation, burial only may be recommended.