Typical radiation exposure from medical diagnostic procedures

When considering radiation exposures from natural, occupational or medicine, you should not add them together, but you can compare them. For example, you should not add medical to occupational exposure because the benefit-risk profiles are different. The benefit of being ‘made well’ (after diagnosis) is higher than simply being employed (where many would argue being paid is the most obvious benefit). Therefore, diagnostic medical exposure tends to be higher than typically received from occupations involving work with ionising radiation.

However, radiation exposure comparisons are useful when evaluating / calculating / or explaining occupational radiation exposure for routine work or reasonably foreseeable accidents. They may also be useful for example in the aviation security industry where whole body back scatter x-ray screening is employed.

Typical radiation exposures from medical diagnostic procedures

The following medical exposures are ‘typical’ for an adult. The unit is ‘effective dose’ (in micro Sv). This means that where an exposure occurs to only part of the body, the ‘exposure risk’ is reported as if it were whole body exposure. This then allows comparisons of overall exposure to be made regardless of location. The reasoning for this is that ‘effective dose’ is a derived term and can be related to excess radiation induced cancer over and above that expected in a population from all other factors (age, diet, environmental etc). This is based on the International Commission on Radiological Protection (ICRP) Publication 103 (which uses the linear no threshold model for radiation protection). There is some debate over the validity of the linear no threshold (LNT) model, however international standards and dose limits are based on ICRP 103.

The rule of thumb - typical radiation exposures from medical diagnostic procedures.

• Chest x-ray – 100 micro Sv
• Stomach x-ray - 600 micro Sv
• Back x-ray – 1000 micro Sv
• Dental x-ray (CT) – 200 micro Sv
• CT (whole body) – 21 mSv
• CT (head) – 2 mSv
• PET/CT (whole body) – 14mSv

Note: for the above values, 1mSv = 1000 micro Sv.

Occupational exposures from radiation related work in the UK

Typical occupational radiation exposures in the UK (including classified and non-classified workers) are now substantially < 1 mSv/year.

Background radiation exposure in the UK

The 2010 (PHE) review of background radiation in the UK suggests an average of 2.7 mSv/ year (nearly 50% of this is radon gas, the rest in descending order is medical, terrestrial gamma rays, cosmic radiation, and intake of naturally occurring radioactive materials other than radon). Interestingly, whilst still of public concern to many, nuclear weapon full out, occupational radiation exposure, and radioactive discharges make up only 0.2% of the total.

Radiation risk factor for use with the comparators

The purpose of this rule of thumb was to provide suggested dose comparators using medical exposures. However, it is worth relating this to excess radiation induced cancer risk (noting our comment above regarding LNT).

For simplification we will use an ICRP summary figure of 5% / Sv (rather than look at specific age-related data). This value is attributed to whole body exposure as outlined above. Since we need to use LNT, it follows that 1mSv it equivalent to a 1:20,000 excess risk of radiation induced cancer. In the UK cancer death from all causes is about 1:4.

Therefore, even if you do not believe in LNT (e.g. you might suggest that radiation health risks are exaggerated), it stands that even with LNT, 1mSv presents a tiny additional risk.