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ICRP: Free the Annals!

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Submitted by Cari Borras, International Organization for Medical Physics
   Commenting as an individual
Document 2005 ICRP Recommendation
 

The document suffers from both conceptual inconsistencies and practical ones. The practical ones are easy to correct, but removing the conceptual ones may be counter-productive as in many cases it would mean significant changes of radiation control regulations in many countries of the world.


Major Issues

1. Need for a revision of ICRP?

As the 2005 ICRP draft states, there are no significant deviations of the radiation protection philosophy between these Recommendations and those from ICRP 60. It is clear that, as scientific knowledge progresses and more and better radiation epidemiological data become available, numerical values associated with radiation protection standards may require updating. This can be done, however, by revising numbers in an already existing publication. The ICRP 60 is by now the basis for radiation control regulations in many countries of both, the industrialized and the developing world, the United States excluded. Regulators resist new standards; their adoption and implementation is fraught with legal battles and is very costly. What is really new in these new recommendations which justify such a lengthy and costly process?

2. Radiobiological basis uncertainties

The text and especially Annex A summarize current radiobiological experimental and epidemiological studies carried out since ICRP 60. Some of the findings do not support current ICRP views. For us, medical physicists, an example is the wR value for low energy x-rays like those used in mammography. Because of the effect of Auger electrons, wR may be greater than 1. Instead, the Commission has chosen to increase the value of wT, declaring the breast tissue more radiosensitive than it was before. There are many other examples of such cases, where in analyzing the results of recent studies, the Commission concludes that the uncertainty associated to the findings is such that, in their judgment, changes are not warranted. If this is the case, why not wait a few more years to change the Recommendations, when the studies have been replicated and the data are more reliable?

3. Averaging and weighting

When data are unreliable (uncertainties are high), the effect of averaging compounds the problem. The Commission acknowledges that cancer incidence is population, gender and age dependent. Furthermore, it is tissue specific. Yet, it chooses to average across all the categories for the sake of “simplicity”. One wonders why go through the trouble of reviewing all the scientific literature if the results are not to be used in a scientific manner. Particularly troublesome is how arbitrary some decisions seem. (A7), (A9), (A14), (A17), (A24), (A28), (A29), (A31), (A36), (A39) are examples of how the Commission has arrived to “ICRP judged values”.

4. Problem with the implementation of dose constraint vs dose limits

The concept of dose constraint certainly is not new. It was introduced in ICRP 60 and it is used by many regulatory agencies throughout the world to optimize radiation protection. One of the objectives of the new Recommendations is to emphasize the role of dose constraints and diminish the role of dose limits. The introduction of the maximum dose constraint, however, makes the distinction between the two parameters terribly confusing, especially in the Summary at the beginning of the document (Table S1 cannot be comprehended as is). Regulators will not know how to implement dose constraints and will tend to adopt dose constraints as limits for the sake of simplicity. In fact, this has already happened in many developing countries, where regulating constraints and limits as separate entities would create a burden beyond the capabilities of the regulatory infrastructure in place. The whole section on dose constraints needs to be rewritten and clear advice on how they are to be implemented, given. In particular, it is essential to re-write paragraph (132) and (S4): “…restrictions on individual dose from specified sources in all situations within their scope… should be applied to the exposure of actual or representative individuals. They provide a level of protection for individuals that should be considered as obligatory and not maintaining these levels of protection should be regarded as a failure.” Other confusing paragraph is (145).

For us, medical physicists, paragraph (164) is bothersome. It suggests to use 0.3 mSv as a dose constraint for the public: “ in case of multiple dominant sources a figure of 0.3 mSv/year would be appropriate”. How is the regulator to know about multiple dominant sources? The rewrite of the NCRP 49 Report encountered the problem of whether to use 1 mSv or 0.25 mSv for public protection limits in shielding design of diagnostic radiology facilities. After months of struggle, the NCRP published Statement No. 10, which clarified: “After a review of the application of the guidance in NCRP (1993) to medical radiation facilities, NCRP has concluded that a suitable source control for shielding individuals in uncontrolled areas in or near medical radiation facilities is an effective dose of 1 mSv in any year. "

Yet, many countries (the UK for instance) have adopted 0.3 mSv as a shielding constraint. If the new ICRP keeps this figure in this paragraph, many more countries will adopt this value. Since the money available for health care is limited, radiological equipment maintenance and/or replacement as well as staff training are sacrificed in order to comply with regulatory requirements for shielding. The net result is a significant detriment to patient management, especially in developing countries.

The problem may lie in the definition of single source (174). How can “the x-ray equipment in a hospital” be a single source? What are we going to do for shielding calculations? Take the “geometrical center of all the x-ray units as an “effective point source” or the edge of the closest one to the point of measurement? Perhaps we need the Commission to help us finding an average and weighted judgment value…


5. Justification of practices

In ICRP 60, justification of practices was a pillar of radiation protection (5). Now (18), the Commission acknowledges that factors other than radiation protection enter into the decision of countries adopting practices involving radiation. This is not new. Still, the way the Commission rationalizes it (10) is not clear at all and it should be re-written. Radiation protection is just one factor for governments to take decisions on legalizing practices, and clearly, not the most important one. The change in emphasis would not be bad, if now [(19), (148), (213)], the Commission were not to insist that medical practices involving radiation need to be justified not only in a generic form [(216), (218)], but individually (219), especially in “complex diagnostic procedures” (which are not defined) and radiation therapy. Regulatory authorities demanding justification of each patient undergoing interventional radiology or radiation therapy is an interference with a medical act and it should not be allowed.

Interestingly, there are inconsistencies on this issue throughout the document. For example (222) states that: “The medical procedures causing patient exposures are clearly justified”. Are they or aren’t they?

Another example (not related to medical exposures) is (161), which seems to lead to the need of justification.

Also (185), which refers to “practices that are already justified in normal conditions”.

6. Patient Protection Optimization and Diagnostic Reference Levels

The last sentence of paragraph (147) should be re-written for greater clarity, as nothing has been said before about the need to reduce dose, and the point the paragraph is trying to make is a very important one.

(223) defines Diagnostic Reference Levels as dose levels against which “unusually high doses” are to be compared. What happens if the doses are too low? The International Basic Safety Standards (IAEA 1996) in regards to Reference Levels (called “Guidance Levels”), also recommended that “corrective actions be taken as necessary if doses or activities fall substantially below the guidance levels and the exposures do not provide useful diagnostic information and do not yield the expected medical benefit to patients”.

7. Operators vs Operating management

In the nuclear power community, operators are the managers of the facility. In the medical field, operators are the individuals who operate a machine such as an x-ray unit or a linear accelerator. To refer to facility managers, the document uses two terms “operators” [(140), (190)] and “operating management” [(156), (174)]. It is recommended that the latter term be used throughout to avoid confusions.

8. Definition of occupational exposure

The International Labor Organization (ILO) defines occupational exposure as that incurred in one’s work, regardless of whether the workers are radiation workers or not. The document in (143) has a slightly stricter definition, which will be contested by the international organizations (FAO, IAEA, ILO, NEA(OECD), PAHO and WHO), which co-sponsored the International Basic Safety Standards and adopted the ILO definition. These organizations will also question paragraph (169).

9. Protection of the environment

This section is not fully developed in the current draft and should be excluded until the issue is scientifically more mature.

Minor Issues

10. Inconsistencies

a. Re-word (49). Not all photons and neutrons are “penetrating”.

b. Medical exposure definition
(141) and (146) should be re-written for greater clarity. The exposure of the staff is occupational exposure, not medical exposure.

c. “Deterministic effects” should be replaced by “tissue reactions” in (247).

d. Figure 2 has the caption “Radiology” under a photograph of a linear accelerator. It should say “Radiation Oncology” or the photo should be changed to show a diagnostic or interventional x-ray unit, including a CT scanner.


11. Typographical/Formatting Errors

a. There are ? signs in (S15), Table S4 and table A2 that need to be replaced by the proper symbol.

b. H needs to be defined in the formulas of (A26) and (A27).

c. (231) is missing words.