At what level is radiation totally safe for our body?

[Rev. Cheeseman]

TL;DR Summary

What is the dose of radiation that is practically harmless for our body

According to this link https://www.sciencemag.org/news/202...sformed-our-understanding-radiation-s-impacts even at radiation doses as low as 0.005 gray, there is still a risk of cancer over long term. I have read some Radiation Effects Research Foundation (RERF), the same organization that was mentioned in the link, studies on Life Span Study and there are death cases recorded among those Hiroshima and Nagasaki bombing victims who exposed to those very low dose radiations (0.005-0.1 grays).

From https://www.ncbi.nlm.nih.gov/books/NBK202000/ referring to "Effect of recent changes in atomic bomb survivor dosimetry on cancer mortality risk estimates" which was written by authors affiliate with RERF,

"By the late 1940s, there were suggestions of an increased risk of leukemia among the atomic bombing survivors; the earliest evidence of an increased leukemia was reported in 1952 (Folley et al., 1952). The latest published LSS mortality data for leukemia are through 2000 and a 46 percent excess (93 excess deaths) are attributable to radiation exposure among the survivors to >0.005 Gy (Preston et al., 2004; Richardson et al., 2009). A clear dose-response relationship exists, with 90 percent of the leukemia deaths among those exposed to doses >1 Gy being excess deaths. Separate analyses also indicated strong dose responses for most subtypes of leukemia except chronic lymphocytic leukemia (Preston et al., 1994).

Because the atomic bombing survivors received whole-body exposure from penetrating radiation, a large number of organ sites were affected. An analysis by Preston et al. (2007) on solid cancer incidence in atomic bombing survivors for the period 1958-1998 showed that an excess of 11 percent of solid cancers are attributed to exposures >0.005 Gy (mean 0.23 Gy). The attributable proportion increases with increasing dose and reaches 48 percent among those who received at least 1 Gy."

But there are several authors who criticized these studies whether the victims actually exposed to very low doses or actually high doses which are fatal. I'll find those articles that criticized the study later.

My question is, how much radiation is truly safe for us that even the possibility of cancer risk over very long term is zero?

 

[anuttarasammyak]

Linear no threshold model https://en.wikipedia.org/wiki/Linear_no-threshold_model#:~:text=The linear no-threshold model,to exposure to ionizing radiation. is often used for the estimation of the exposure risks.

 

[hutchphd]

Like nearly everything in the real world, there are no bright lines. There may be a no-harm threshold, there may not be. The statistical diifficulties of studying low probability events are obvious.
Life is a "crap shoot", you estimate each step, commit, and then repeat. Eventually you get subsumed..

 

[Rev. Cheeseman]

Like nearly everything in the real world, there are no bright lines. There may be a no-harm threshold, there may not be. The statistical diifficulties of studying low probability events are obvious.
Life is a "crap shoot", you estimate each step, commit, and then repeat. Eventually you get subsumed..

So, that means next time we should be careful and think many times before taking X-rays, CT scans, etc. although their radiation doses are very low?

 

[hutchphd]

Not necessarily. If the alternative is die from some horrible suspected disease, the decision is easy! (I recently had a full body CT scan on this basis...it was enough radiation that a good estimate could be made of the possible effects). Also radiation exposure is likely to be more consequential, eventually, if you are young. But there is no firm evidence that a threshold "no-harm" level exists. But clearly more radiation is worse than less for clinical exposures.
The more difficult assessments are environmental exposures, and bioactive isotopes which may concentrate. The evaluation of nuclear power tradeoffs are made more difficult by these unknowns with respect to small exposures to large populations.

 

[Vanadium 50]

Insisting on absolute safety is unproductive. At some point the drive to the doctor's to get an X-ray exceeds the risk of the X-ray itself. Are you going to forego bananas? (K-40 source) Marriage? (sleeping next to a K-40 source) Live in a basement? (cosmic rays) Not live in a basement? (radon)

The fact of the matter is that at low doses the risk is so small as to be impossible to measure. We can create models, like LNT, but we cannot verify them.

 

[Choppy]

So, that means next time we should be careful and think many times before taking X-rays, CT scans, etc. although their radiation doses are very low?

Just to add to what's been said, it's important to remember that in radiology there are guidelines for the use of imaging modalities that use ionizing radiation that help physicians weight the risks and benefits of imaging exams. See for example:
https://www.imagewisely.org/
https://www.imagegently.org/

Generally we're most concerned about how things work on a statistical basis. A whole, we have to look at populations of people. If you take a cohort of 10,000 women for example and perform mammography exams to screen for breast cancer--in how many of those 10,000 will a cancer occur because of the systematic exposure that otherwise wouldn't have? And you have to weigh that against the number of cases of breast cancer you will discover (and effectively treat and cure) because of the screening.

From an individual point of view, it's important to consider radiation exposures in terms of background dose. Most people receive about 2-3 mSv per year, from many different sources (as V50 alluded to: terrestrial sources like radon, potassium, cosmic rays, etc.) Some people can receive ten or even one hundred times this average amount without detrimental effects. People in Ramsar Iran, for example can receive up to 260 mSv annually and there is even some evidence to suggest that the higher background doses may have some protective effects, although these are not commonly factored into radiation protection models.

Radiation causes harm by inducing genetic damage at the cellular level--it induces free radicals that interact with the DNA and cause lesions that keep it from functioning. If the DNA is not repaired properly, in the long term, that can lead to the induction of cancer. But radiation is not the only agent that induces genetic damage. Even cellular respiration itself can generate reactive oxygen species that will lead to genetic damage. So at some point, the harm done by low doses of radiation is just noise in the system.

 

[jim mcnamara]

@Choppy said

Even cellular respiration itself can generate reactive oxygen species that will lead to genetic damage

This is called oxidative stress. Mitochondrial damage occurs from ROS (reactive oxygen species). There are builtin anti-oxidants like glutathione that mop up the mess - but too much ROS and cells get damaged anyway. DNA can get altered for example.

See:https://en.wikipedia.org/wiki/Oxidative_stress
See the red stuff in the graphic top right? Those are the points (biochemical steps) where this damage can start.

 

[Keith_McClary]

When X-Rays Were All the Rage, a Trip to the Shoe Store Was Dangerously Illuminating

The shoe-fitting fluoroscope was unnecessary and hazardous, but kids loved it

Anyone else remember thinking these were really cool?

 

[hutchphd]

When X-Rays Were All the Rage, a Trip to the Shoe Store Was Dangerously IlluminatingAnyone else remember thinking these were really cool?

Luckily I just missed out on them. My oldest brother,now an M.D., remembers in horror a number of fascinating trips to the shoe store.^