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When considering all these risk factors, you should take into account that all nuclear medicine and X-ray diagnostic procedures have been classified by the International Commission on Radiological Protection (ICRP) as having either negligible, minimal, very low or low risk. They emphasise that the risks represent very small additions to the 1 in 3 chance we all have of getting cancer. In addition, when prescribing the scan, your doctor will have weighed up the benefit of improved diagnosis of your condition against the small risk of the radiation exposure. If you are still concerned about this aspect, you should ask your doctor to explain the benefits and risks involved.
Typical effective doses, equivalent periods of natural background radiation and lifetime fatal cancer risks from diagnostic medical exposures in the 1990’s (figures from the National Radiation Protection Board (NRPB), UK). These figures are also used by the International Commission on Radiological Protection (ICRP) in their report: “Radiation and your patient: a guide for Medical Practitioners”)
| Diagnostic Procedure | Typical effective dose (mSv) | Equivalent period of natural background radiation* | Risk of fatal cancer per examination** |
|---|---|---|---|
| X-Ray examinations | |||
| Limbs and joints (except hips) | < 0.01 | < 1.5 days | 1 in a few million |
| Teeth (panoramic) | 0.01 | < 1.5 days | 1 in 2 million |
| Chest (single PA film) | 0.02 | 3 days | 1 in a million |
| Cervical spine (neck) | 0.08 | 2 weeks | 1 in 200 000 |
| Hip | 0.3 | 7 weeks | 1 in 67 000 |
| Thoracic spine or abdomen | 0.7 | 4 months | 1 in 30 000 |
| Barium swallow | 1.5 | 8 months | 1 in 13 000 |
| IVU (kidneys and bladder) | 2.5 | 14 months | 1 in 8000 |
| Barium enema | 7 | 3.2 years | 1 in 3000 |
| CT head | 2 | 1 year | 1 in 10 000 |
| CT abdomen/pelvis | 10 | 4.5 years | 1 in 2000 |
| Radionuclide Studies | |||
| Lung ventilation (81mKr) | 0.1*** | 2.4 weeks | 1 in 200 000 |
| Lung perfusion (99mTc) | 1 | 6 months | 1 in 20 000 |
| Kidney (99mTc) | 1 | 6 months | 1 in 200 000 |
| Thyroid (99mTc) | 1 | 6 months | 1 in 200 000 |
| Bone (99mTc) | 4 | 2.3 years | 1 in 5000 |
| Dynamic cardiac (99mTc) | 6 | 2.7 years | 1 in 3300 |
| Myocardial perfusion (201Tl) | 18 | 8 years | 1 in 1100 |
* UK average = 2.2 mSv per year: Regional averages range from 1.5 to 7.5 mSv per year
** Approximate lifetime risk for patients from 16 to 69 years old; for paediatric patients, multiply risks by about 2; for geriatric patients divide risks by about 5.
*** the risk of death by exposure to 0.1 mSv is the same as that of smoking one cigarette or drinking half a bottle of wine.
Compare these risks with the risks of everyday activities