Lung cancer fatality risk and smoking habits

It is well known that there is a strong relationship between the smokers and the incidence and lung cancer fatality. A US lung cancer mortality study indicated the mortality rate increased with age and the number of fatalities from lung cancer among smokers increased very significantly as compared to non-smokers.

Mortality rate per 100,000 person-years

Age group                Non-smokers          Smokers

55 – 59 y                   5.3                              206

60 – 64 y                   11.6                           361

65 – 69 y                   21.5                           581

70 – 74 y                   34.9                           909

It is indicated that the incidence of lung cancer is more prevalent amongst the uranium miners who are exposed to radon (radioactive gaseous decay product from uranium and thorium series) and its decay products. The risk of incidence of lung cancer varies with the different smoking habits. Studies have indicated that there is enhancement (synergistic effect) in the lung cancer risk due to radon exposure and the smoking habits of the exposed persons.

This means risk of lung cancer resulting from unit radiation dose due to exposure to radon for people who are smokers is substantially higher than that of people who never smoked.

Exposure to radon is much more injurious to heath if you are a smoker. 

LNT approach is not justified for radiation protection

LNT controversy is appearing again and again in the scientific forums worldwide. In every forum it is said that there is no concrete evidence and justification to accept LNT approach for radiation protection purposes. Finally, it is said that in-spite of all the controversies, LNT is accepted in the radiation protection system since it is easier to manage the radiation doses, and for decision taking regarding w.r.t a practice or procedure.

Why this is forced acceptance? And what cost? Billions of dollars?

As a well-informed radiation protection professional, I am strongly of the opinion that:

1.     ICRP has recommended one-year dose limit of 50 mSv for occupational workers in the System of Dose Limitation. It is assumed that there are no clinically observable biological effects up to a dose of 100 mSv.

Accept 50 mSv as the threshold dose for stochastic effect.

2.     As a measure of good work practice, optimise the occupational exposures in a dose band of 10 to 50 mSv/y. Optimization to be carried out only up to a risk level keeping in view of the overall risk in perspective. 

[10 mSv is the annual dose accepted in radon at work places.] 

ALARA / ALARP / ALATA

The aim of radiological protection must be to prevent unnecessary exposures and to keep the exposures below the internationally accepted ICRP dose limits. It is not possible to control the exposures lower than the background radiation dose levels and hence zero or even close to zero exposures to occupational radiation workers is neither possible or justifiable. Due to its acceptance of LNT theory for radiological protection, and use of As Low As Reasonably Achievable (ALARA) approach, ICRP is over-cautious in its recommendation of ALARA. However, over the years, ALARA has become a regulatory requirement!

The recommendation of ALARA is based on the optimization of the protection taking into account the socio-economic considerations and should remain as the best possible level of protection under the prevailing circumstances. This statement makes ALARA a very uncertain requirement which is difficult to quantify.  

Risk must be averted unless there is gross disproportion between the cost in terms of averting the risk and the benefits of averting such a risk. A proportionate approach - ALARP is the term used in UK legislation, as a requirement that risks to health must be reduced to a level that is As Low As Reasonably Practicable (ALARP). It is the tolerable risk level, which is in- between normally unacceptable and broadly acceptable levels.

 

The “As Low As Technically Achievable (ALATA)” approach is to take the protection level to a level that may be achieved using “World’s Best Practice” utilizing grossly disproportional amount of resources (manpower, money and technology) to reduce exposures which has trivial amount of risk. 

Comment: One sensible and practical approach is to get away from the ALARA, ALARP and ALATA, and ensure that the occupational exposures are strictly maintained below the scientifically derived ICRP dose limits. This will be uniformly in line with the chemical industry where the exposures to chemicals, including carcinogens are regulated by the Threshold Limit Values (TLVs) / Permissible Exposure Limits (PELs). The TLV/PEL of a chemical substance is an exposure level to which a work worker can be exposed for a working lifetime without adverse health effects. The regulation will be through use of SOPs, regular monitoring, periodic review and ensuring compliance. 

2015 Nobel Prize in chemistry for work on DNA repair

Three scientists from Sweden, US and Turkey won the most prestigious Noble Prize for their works on DNA repair mechanism. The three scientists are: Swedish citizen, Prof. Tomas Lindahl (UK); US citizen Prof. Paul Modrich (USA) and US and Turkish citizen, Prof. Aziz Sancar (USA). Prize money of 8 million Swedish Krona to be shared equally between them.

Our body consists of cells of different types. Deoxyribonucleic acid (DNA), stored in the nucleus of every cell, contains genetic code written in chemicals.  DNA replicates itself during cell division. During this process something can go wrong and there can be damage to the DNA molecule. The DNA damage (called mutation) can also take place due to many other reasons, such as exposure to some chemicals, radiation and many other environmental pollutants, both physical and chemical.  The repair mechanism is able to repair this continuous damage of the DNA due to variety of reasons. Prof. Lindahl studied the degeneration or DNA decay over time and how the DNA repair takes place at molecular level.  

Enzymes, viz., specialized protein molecules, act as media in DNA repair through chemical reactions taking place at molecular level. The work carried out by these scientists helped in understanding the working of these repair mechanisms; and will help in better understanding of the chemistry behind ageing process and other diseases, including cancer.

One of the three scientists, Prof. Aziz Sancar worked on repair mechanism of the DNA damage caused by the exposure to visible light and UV radiation. He worked on the repair mechanism which made DNA in bacteria exposed to lethal doses of UV radiation to recover under blue light. However, in mammalian cells, a different repair mechanism, called nucleotide excision repair works. However, there is a possibility of a tiny mismatch during the repair of damaged DNA strands. There exists in the cells, enzymes which repair these mismatches in the DNA strands. Prof. Paul Modrich studied the mechanisms correcting such mismatches.   

My comment: The scientists have been doing great work for years on this all important and complex subject of repair of damaged DNA. The damage has been taking place spontaneously and also due to exposure to other agents, including natural background radiation. I failed to understand how some one can say that the cancer cases seen in the population is due to exposure to low level ionizing radiation from nuclear facilities?  It is time that researchers experimentally prove, beyond doubt, that there is no linear no-threshold (LNT) relationship between exposure to radiation and the cancer. 

News item in Sunday Times (Sept. 7, 2014) Cancer behind 70% deaths in India’s atomic energy hubs

The change in the cell's genetic material may occur spontaneously or be brought on by an agent (a carcinogen) that causes cancer ultimately. There are hundreds of reasons such as pollution, family history, cigarette smoking, intake of alcohol, exhausts from vehicles, etc for initiation of mutation in the body. As compared to these, radiation is a weak carcinogen.

 

It is a well-known fact that aging is associated with a number of events at the molecular, cellular and physiologic levels in our body that influence carcinogenesis and subsequent cancer growth. It is also well documented that the incidence of malignant tumors increases progressively with age, in both animals and humans. Cancer is an old-age disease. 

 

It is experimentally known that it is rather impossible to detect clinically any biological effects caused by radiation up to the cumulative radiation dose of 100 mSv. Dose limits for occupational workers are fixed on this basis, and assuming a linear non-threshold relationship between dose and its effect. This assumption is not based on sound experimental results. The well-known protective mechanisms in the body such as biological repair mechanism, adaptive response of the cells, and reported positive biological effects (radiation hormesis) which are prevalent at low dose exposure situations, are not considered by the international organizations (such as ICRP) while formulating the limits. This is an unrealistic assumption and should be challenged scientifically.

 

A clearer understanding of these events will help in predicting, and scientifically explaining the incidences of cancer.

 

The radiation doses received by workers in most of the DAE facilities are in the range of natural background radiation dose to which all human being are exposed. The increase, if at all true, may not be related to the small radiation doses received by the workers and the members of the public living near nuclear facilities. The risk from the exposures is trivial.  

 

It is reported that majority of deaths of persons in DAE centres are caused from cancer. If this is true, department should investigate the reasons other than radiation exposure for such a trend.

 

One most probable reason is the excellent health care facilities for DAE employees, families and the retirees might have caused significant increase in the life expectancy, and the malignancy is likely to be detected mostly in elder people. This can be confirmed by the age at which cancer is diagnosed among the people. There can be only some exceptions like childhood cancers.

 

We should be telling the truth to the public that cancer is an OLD-AGE DISEASE, nothing much to do radiation exposure. Millions of people are dying of cancers related to smoking, use of tobacco and consumption of alcohol!

Skin dose estimates

The personal dose equivalent at 10 mm depth, Hp(10), is used to provide an estimate of effective dose for comparison with the appropriate dose limits. As Hp (0.07) is used to estimate the equivalent dose to skin, it should be used for extremity monitoring, where the skin dose (500 mSv) is the limiting quantity. It is also possible to use the TLD cards to assess beta ray doses provided that the beta ray energy is greater than 70 keV. Beta rays below this energy will not reach the TLD card. 

In nuclear fuel cycle facilities, personnel are exposed to various types of radionuclides of different energies. Radiation environment is different in different facilities. Skin dose for the workers can be significant. Estimate of the skin dose is not easy. It depends on energy spectrum and the dosimeter used. Often, one has to calibrate the dosimety system for a particular facility. 

The absorbed doses by the TLD below the open window of the cassette used to hold the card, and the TLD under the plastic filter are used to estimate the beta component of the exposure. The estimates needs to be multiplied by the tissue weighting factor for the skin (0.01) to get the contribution of the skin dose to the whole body dose. This needs to done and entered in the personnel dose records, particularly so for the workers in: nuclear fuel production and fabrication facilities; in fuel reprocessing plants; workers near spent fuel storage bays and operators of radiopharmaceutical production facilities.       

Ethical aspects of radiological protection

Virtue ethics

 

It is well known that early applications of radiation resulted in severe injuries to the exposed personnel. Examples are: Use of X-rays and use of radium compounds for painting the watch dials. Such effects are now known as deterministic effects of radiation exposure. For radiological protection, under such situations, the control was to reduce the dose levels to the individuals to prevent such deterministic effects. Virtue ethics is concerned with the actions for complete well-being of a person, and a person-based decision to act and provide guidance to prevent severe health effects in all such radiation exposure situations.  

 

Utilitarian approach to ethics

 

In this approach, the consequences of a given radiation exposure is assessed. Action which produces the maximum benefits over harms for everyone affected or exposed is accepted as the morally right course of action. All the available options and the general balance of short-term and long-term benefit over the harm to all persons are considered. This is the justification process based on cost-benefit analysis. Dose limits, based on stochastic considerations provide the upper-bounds for optimization.

 

Duty-based or Deontological ethics

Duty-based (Deontological) ethics are concerned with what people do and not with the consequences of their actions. People have a duty to do the right thing or take right decision even if it produces consequences which may not be acceptable to all.  The Duty-based ethical systems expects due regard to be given to even to small group of persons even if the actions are at odds with the interests of a larger group. Dose constraints/risk constraints are considered for optimization of protection.

The current recommendations of the ICRP emphasize more duty-based ethics, giving more importance to the control of individual doses than to the collective dose and cost-benefit analysis. Exposure to individuals is controlled by the use of dose/risk constraints on multiple sources of exposure.