|Comments of the Japanese Society of Radiological Technology (JSRT) on the draft of the new recommendations released in June 2006
1. General comment
Based on The 3rd Asian Regional Conference on the Evolution of the System of Radiation Protection of OECD/NEA, we would like to comment on the draft recommendations from the viewpoint of the medical radiation safety.
It is expected that some coefficients will be improved in new recommendations based on new knowledge. The revises of technical terms, units and unit symbols are also appreciable as the results of re-considering of the concept of radiation protection. However, the terminological change might bring undesirable confusions to the medical field. Therefore, in order to make confusion minimum, the recommendations are required to show the reasons of the changes and the points that changed clearly.
2. LNT, paragraph 30
Safety and danger can only be indicated in probability. Regarding risk as probability is accepted widely. LNT assumes a risk becomes small, simply when exposure is small. The ICRP's statement of "It is assumed that any exposure is capable of causing an effect, with no threshold (see FD C-1)." is not appropriate expression. In order not to induce too much and unnecessary anxiety to a patient, LNT should be explained appropriately. We do not have to cope with a tiny risk seriously. The meaning that adheres to the insignificant uncertainty of trivial risk presumption is small. It is clear that there is no excess risk more than the certain level at an exposure of a low dose. For this reason, we would recommend to explain logically that LNT is not irrational as a tool on radiation protection.
3. The terms of radiation effect, paragraph 48
3.1 tissue reactions
The term "non-stochastic effects" and "deterministic effects" were too notional for medical practitioners. The proposed term "tissue reactions" is more familiar to medical practitioners as Prof. Ishiguchi mentioned at the conference.
The usage of the expression, which is easy to understand, is accepted well in the medical field.
On the hand, students might confuse thinking that the development of symptoms of tissue reactions is also probabilistic. Therefore it should be explained the historical background for the changes of the technical term. Medical practitioners are not interesting in the change of technical terms without appropriate explanation. Therefore the reasons and historical backgrounds for the changes of terms should be added briefly for they can understand easily.
3.2 cancer and heritable effects
Since misunderstanding that the effect size of both might be the same might occur, the term that combines together cancer and heritable effect is not suitable for the title of the chapter or a technical term as Prof. Ishiguchi and Dr. Nagataki mentioned.
4. Medical exposure of patients, paragraph 136
4.1 The ICRP's statement of “The use of effective dose for assessing the exposure of patients has severe limitations that must be considered when quantifying medical exposure.” is considered to be insufficient for explanation. What is necessary is to select an appropriate radiation dose index regarding the kind of concerned radiation effect. We shared the committee’s view that there is a limit in estimating the risk using a low effective dose because of the limitation of scientific knowledge as being stated in this draft. However, it is not "severe limitations" in clinical situation. We do not have to worry about the accuracy of risk presumption too much when the radiation dose is low. Therefore the explanation of “severe limitations” is expected to clarify hopefully.
4.2 The ICRP's statement of “Effective dose can be of some value for comparing doses from different diagnostic and therapeutic procedures and for comparing the use of similar technologies and procedures in different hospitals and countries as well as from the use of different technologies for the same medical examination.” is thought that a part of expression is not appropriate. It is important to decrease the risk of the tissue reaction at the normal organs near the cancer in ordinary radiation therapy. The effective dose is also one of the indexes for the optimization for the advanced radiation therapy, although the role of the effective dose in radiation therapy seems to be very small. For this reason, the effective dose is not adequate parameter to compare two or more plans in ordinary radiation therapy. Therefore it seems to be appropriate to add a certain reservation such as “therapeutic procedures in some situations”
4.3 The ICRP's statement of “For planning the exposure of patients and risk-benefit assessments, however, the equivalent dose or the absorbed dose to irradiated tissues is the more relevant quantity.” is also thought that a part of expression is not appropriate. In diagnosis, control of a carcinogenic risk is the purpose of the radiation dose assessment. In these cases, the absorbed doses of different specified regions and the equivalent dose of certain organs have to be taken into consideration. Therefore, an effective dose might be appropriate for this purpose.
5. Equivalent doses and absorbed dose in medical exposure of patients, paragraph 137
5.1 In medical radiation, even if the effective dose and the equivalent dose are small, an absorbed dose to specified region might be relatively high as mentioned in paragraph 97. Therefore it seems to be more appropriate to replace the ICRP's statement of “can result in appreciable equivalent doses to local tissues” to ”can result in appreciable absorbed doses to local tissues” in this context.
5.2 Medical staff can easily understand the concept and difference of equivalent dose and effective dose. However, it is necessary to avoid misunderstandings that are likely to happen among students. Likewise, to avoid confusions and urge proper understanding, the introduction of subscripts for Sv as effective dose, equivalent dose and dose equivalent might be considered as a similar point of view of comments from Dr. Kumamoto and Dr. Fujimoto on GyEq for the region of high dose by neutron and high-LET radiations. The subscript is expected to minimize the correction and confusion.
6. Effective dose from medical exposure of patients, paragraph 138
The ICRP's statement of “The assessment and interpretation of effective dose from medical exposure of patients is very problematic when organs and tissues receive only partial exposure or a very heterogeneous exposure which is the case especially in x-ray diagnostics.” is considered to be insufficient for explanation. An effective dose seems to be adequate indicator of radiation dose as medical radiation is unequal for whole body. On the other hand we do not have to estimate the effective dose with high accuracy because medical exposure causes relatively low dose and bring much benefit. Thus, it does not seem to be appropriate to describe, " is very problematic".
7. Justification, paragraph 191
Radiology has been developing. In connection with these developments, it seems that a physician might need advice of the specialist in order to perform radiological protection properly, and to conduct clinical decision analysis appropriately. Therefore the specialist of radiation such as a radiological technologist or a medical physicist should support physicians and patients to make a good decision-making based on the scientific information especially in pediatric radiology.