ShotOne, as far as “the implication that the radiation risk experienced by flight crew is very low” is concerned, my points are that (1) radiation risk is dependent upon specific variables: radiation type, dose, and dose-rate, and (2) below a certain threshold, radiation exposure has little risk or even a benign effect. It all depends on the numbers in each person’s case. Of course, if a pilot’s exposure exceeds that threshold, there would be an X probability of cancer.
The article and personal radiation-dose computation worksheet links provided in my earlier posts provide some perspective.
It is quite probable that a significant level (especially at high altitudes) of long-duration-UV exposure can cause skin cancer.
Paradoxically, sunlight is not the only significant variable. As my dermatologist tells me, skin melanoma often occurs without lifetime high exposure to sunlight. There are other factors involved such as genetic predisposition. Nonetheless, since I live in Florida, I try to minimize sun exposure.
Speaking more generally, the devil is in the details. Different (other) kinds of radiation (alpha, beta, gamma) have different biological effects. According to MIT News: “Because x-rays and gamma rays are less damaging to tissue than neutrons or alpha particles, a conversion factor is used to translate the rad or gray into other units such as rem (from Radiation Equivalent Man) or sieverts, which are used to express the biological impact.”
Another variable is dose rate. The same dose received within a small span of time has a greater negative effect than that received during a much longer duration.
There is growing evidence supporting radiation hormesis, the theory that low doses are harmless and may even have a beneficial effect by stimulating cell-repair mechanisms. Science sometimes takes a long time to change course, and challenging its conventional wisdom in a highly contradictory way means opposing its massive inertia, which is like that of a super tanker.
The scientific challenge is to define more precisely the boundary between the harmful and beneficial levels of both radiation dose and dose-rates, so that we can transition from the woolly generalization that all radiation is bad.
That can lead to use of low-level radiation to improve health in specific, scientifically proven contexts, and also reduce overextended radiation protection regulation that unnecessarily increases the cost of compliance for industry and government.
The current Linear No-Threshold (LNT) model underlying worldwide radiation protection standards is imprecise and clumsy. As Wikipedia (which provides an excellent overview of the LNT pros and cons) notes:
“The linear no-threshold model (LNT) is a model used in radiation protection to quantify radiation exposure and set regulatory limits. It assumes that the long term, biological damage caused by ionizing radiation (essentially the cancer risk) is directly proportional to the dose.
This allows the summation by dosimeters of all radiation exposure, without taking into consideration dose levels or dose rates. In other words, radiation is always considered harmful with no safety threshold, and the sum of several very small exposures are considered to have the same effect as one larger exposure (response linearity).” https://en.wikipedia.org/wiki/Linear...el#Controversy
According to the World Nuclear Association:
“Some of the ultraviolet (UV) radiation from the sun is considered ionizing radiation, and provides a starting point in considering its effects. Sunlight UV is important in producing vitamin D in humans, but too much exposure produces sunburn and, potentially, skin cancer. Skin tissue is damaged, and that damage to DNA may not be repaired properly, so that over time, cancer develops and may be fatal. Adaptation from repeated low exposure can decrease vulnerability. . . . Our knowledge of the effects of shorter-wavelength ionizing radiation from atomic nuclei derives primarily from groups of people who have received high doses. The main difference from UV radiation is that beta, gamma and X-rays can penetrate the skin. The risk associated with large doses of this ionizing radiation is relatively well established.
However, the effects, and any risks associated with doses under about 200 mSv [20 rem], are less obvious because of the large underlying incidence of cancer caused by other factors. Benefits of lower doses have long been recognised, though radiation protection standards assume that any dose of radiation, no matter how small, involves a possible risk to human health. However, available scientific evidence does not indicate any cancer risk or immediate effects at doses below 100 mSv [10 rem] per year. At low levels of exposure, the body's natural mechanisms usually repair radiation damage to DNA in cells soon after it occurs (see following section on low-level radiation). However, high-level irradiation overwhelms those repair mechanisms and is harmful. Dose rate is as important as overall dose.” Radiation | Nuclear Radiation | Ionizing Radiation | Health Effects - World Nuclear Association
More documentation about hormesis by other sources:
“In 1990, the ICRP [International Commission on Radiological Protection] (in its Publication 60) conceded that hormesis might exist but said that “the available data on hormesis are not sufficient to take them into account in radiological protection.” With the publication of a great deal of evidence on hormesis since 1990, the converse is now true, viz: that the ICRP would need to be very confident that radiation hormesis does not occur if it is going to recommend the assumption of LNT [the Linear No-Threshold concept].” --Dr. Donald J. Higson, Australasian Radiation Protection Society
ICRP: Consultation view comment
“The conclusion of zero threshold dose for carcinogenic effects of radiation in the recent updated report on the atomic bomb survivor cancer mortality data appears to be unjustified and may be the result of the restrictive functional forms that were used to fit the data. Also,
the shape of the dose-response observed in the recent update of atomic bomb survivor data is clearly non-linear with the significant reduction in cancer mortality rate in the dose range of 0.3 Gy to 0.7 Gy.
This raises doubts about the LNT model and possibly shows evidence for the phenomenon of radiation hormesis when a correction is applied for a likely bias in the baseline cancer mortality rate. Though the use of radiation hormesis was proposed more than three decades ago as a method of reducing cancers, no prospective human cancer prevention studies have been conducted so far to determine its validity due to carcinogenic concerns based on the LNT model. . . . Low dose radiation may also be helpful in improving outcomes in cancer patients by cure of early stage cancers, as an adjuvant to standard radiation therapy to improve tumor control and reduce metastases, and to reduce the incidence of second cancers. Pilot clinical trials are needed to determine the effectiveness of low dose radiation in these applications. Success in such clinical trials can help to reduce the concerns regarding low dose radiation and enable the study of cancer prevention using radiation hormesis.”--”Linear No-Threshold Model VS. Radiation Hormesis,” by Mohan Doss, PhD, Associate Professor, Fox Chase Cancer Center, Philadelphia, PA
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3834742/