Saturday, September 12, 2015

Cockroaches: Hiroshima & Health Maintenance

5:29:45 am Mountain War Time on July 16, 1945
Los Alamos National Laboratory
On a Monday in August 1945, Little Boy was dropped on Hiroshima by the crew of an American B-29 bomber Enola Gay. Around 80,000 people were killed immediately. By the end of that year another 100 to 150 thousand died from radiation. It was estimated though that at least 43 % of the cockroach population survived.

For nearly 300 million years, most species of cockroaches (and there are nearly 4000 of them) did not evolve at all and the chances are that they will be around in another 300 million years.

The ability of cockroaches to survive a nuclear winter has drifted into urban mythology, so much so that the Discovery Channel found it necessary to 'bust' that myth.

Yes, the cockroach, being an insect, can withstand at least 6 times the radiation a human can. It is still no match for the fruit fly, one of the most studied insects in biology.

In the meantime a good friend from my Hong Kong University Medical School days alerted me to some important but little publicized fact on Health Maintenance.
“It is so common nowadays for doctors to order a CT scan for this and that, without knowing that the amount of radiation that the patients are exposed to may be equivalent to the radiation exposure experienced by the Japanese survivors of the atomic bombs in the 1940s, which was estimated to be in the region of 5 to 20 millisieverts (mSv).”

Now, one thing is for sure, we are not cockroaches and certainly not fruit flies. Should we not be more cautious?

My friend, an eminent cardiologist, is two years my senior at Medical School. He said:

“During my class reunion (HKU Medics '66) in November 2006, one of my classmates drew me aside and showed me the reports of coronary CT angiograms (CTA) that he and his wife went through as routine checkup and asked me for my comment. Did they have any coronary artery disease risk factors? None.

On my recent visit to Hong Kong in February this year, one of our friends who is an anesthesiologist in her mid-forties casually mentioned that her family doctor ordered a CTA for her when she complained of dyspepsia due to acute gastritis. Neither she nor her family doctor realized that the risk of cancer of breast or lung cancer from the CTA may be as high as between 1:284 to 1:466 12 years from now, which is scary.”

In December 2006, my friend was indeed asked to write a review article on the Risks and Benefits of Coronary CT Angiography (CTA) for the Journal of Hong Kong College of Cardiology. This is an extract:

“The risk of cancer from radiation exposure in CTA has been estimated to be 1:1000 to 1:2000, and the time lapse between radiation exposure and onset on cancer was reported to be 2 to 5 years for acute leukemia and 10 to 20 years for solid tumours such as breast and lung cancers.

In July 2007, an article was published in the Journal of American Medical Association entitled Estimated Risk of Cancer Associated with Radiation Exposure from 64-Slice Computed Tomograohy Coronary Angiogram (by AJ Einstein, MJ Henzlova and S Rajagopalan, JAMA July 2007, Vol 298, No.3, 317-323), which showed that a certain subset of the population are more vulnerable to the risk of cancer. Children, who are even more susceptible, were not included in the study.

Using data provided in the Biological Effects of Ionizing Radiation (BEIR) VII phase 2 Report (of the National Academy of Sciences, USA), the authors calculated that the lifetime attributable risk (LAR) of cancer from radiation exposure in CTA was much higher in young and female subjects, being 1:143 for the 20 year-olds, 1: 284 for the 40 year-olds and 1:466 for the 60 year-olds. Breast and lung cancers will account for 80-85% of all radiation induced cancers in women. The corresponding figures of cancer risks for men were 1:686, 1:1007 and 1:1241 respectively.”

I am sure the world will be a better place if we all share our knowledge. We cannot know all but we certainly can share all.

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