Flying free of skin cancer – Part 2

Brought to You by - Brent Taylor, MD, Premiere Dermatology and Mohs Surgery of Atlanta

In last month’s article about aviation and skin cancer, we looked at FAA regulations relating to pilots, melanomas, and the importance of early detection. This month, we’ll look at the question of whether flying in general causes skin cancer. Are you assuming much risk of cancer by flying at 35,000 feet? What if you’re a frequent flier?

We know that pilots develop skin cancer at a higher rate than the general population. A large Nordic study of male pilots found that they developed 130% more melanomas than expected, 110% more squamous cell skin cancers than expected and 150% more basal cell skin cancers than expected. The risk of skin cancer increased with the time since first employment, the number of flight hours, and the estimated radiation dose from being at altitude.

What is not known is whether radiation received during flight is to blame for these skin cancers. Correlation does not always mean causation, and just because pilots had higher rates of skin cancer doesn’t mean that cosmic radiation solely is to blame. The “flight environment” includes a combination of exposures including ultraviolet light, decreased oxygen levels, ozone, disinfectants and other hazards and stressors that are uniquely combined in aviation. These confounding variables make confident blame of any one hazard difficult to prove. Still, cosmic radiation is known to cause DNA damage and is worth examining, especially given how much flying is being done by flight crew and passengers alike.

Both the atmosphere and earth’s magnetic fields provide protection against cosmic radiation. Radiation levels approximately double for every 4500 feet of increased elevation due to thinner atmosphere. Due to magnetic fields shielding less at earth’s magnetic poles, radiation levels are approximately double at the poles compared with the equator. The most radiation occurs during a flight at high altitude over one of the earth’s poles. In the European Union, airlines attempt to keep radiation levels below 6mSv per year. How much is a mSv?

We all receive about 1 mSv just from living at sea level in a year. We average an additional 1 to 2mSv from other sources such as flying, medical and dental x-rays, etc.

The International Commission on Radiological Protection (ICRP) recommends no more than 20mSv per year for people working in occupations such as nuclear power or radiology that involve radiation exposure. How did they come up with 20mSv?

A generally accepted figure is that every 1000mSv of excess radiation increases one’s risk of dying from cancer by 5%. The ICRP assumed that 5% excess risk of dying from cancer is a reasonable cutoff and that few people will spend more than 50 years in any given career. 1000mSv divided by 50 years is 20mSv per year.

A pilot flying at 35,000 feet for 1000 hours each year can expect between 3 and 5mSv of excess cosmic radiation per year. This means that a pilot who works 40 years can expect 120 to 200mSv of excess radiation on average which means that a pilot’s chance of dying from cancer might be increased by about 0.6% to 1% on average. Of course, the chance of developing cancer but not dying from it is higher.

Is this risk acceptable?

My assumption is that everyone in the United States drives, and we are all willing (reluctantly) to assume the risk of death that comes from driving. Driving risk is a useful benchmark when contemplating other types of risk. Let’s assume you wouldn’t want to raise your risk of dying from cancer any more than your current risk of an automobile death, which is a lifetime risk of 1% in the United States. Well, about 200mSv of radiation exposure is expected to result in that increase. Assuming 0.004mSv per hour of commercial air travel, you would have to fly 50,000 hours in your lifetime to increase your risk of cancer death from high altitude radiation enough to equal your risk of dying in an automobile accident. Almost no pilot will reach that number, and certainly few if any passengers approach that number.

A more significant risk is probably unnecessary medical radiation. See https://www.health.harvard.edu/ cancer/radiation-risk-from-medicalimaging for a complete breakdown of radiation from common medical tests. Food for thought is that each CT scan of the chest averages 7mSv. A whole-body CT scan averages 20mSV or more, and a PET/CT scan averages about 25mSv. If a patient needs the scan, then the patient needs the scan. But unnecessary scans involving radiation are to be avoided. 25mSv is more than the annual radiation limit of 20mSv recommended by the ICRP, and someone receiving a PET-CT scan receives that radiation all in a single day.

When compared with the risks of driving a car or the risk of radiation from medical imaging, the risks of cosmic radiation while flying appear acceptable. Sit back and enjoy your flight.