Radiation Risk from CT Scan

Dr. Khalid Shokor Mahmood

Computed tomography (CT) scans are widely used and are an invaluable tool for medical imaging.

However, the possible overuse of CT scans and the variability in radiation doses might subsequently lead to thousands of cases of cancer.

Sir Godfrey Hounsfield (1919-2004),Nobel Prize, 1979

In September 1971, CT scanning was introduced into medical practice

Radiation Absorption

The biological effect of radiation can be described by the roentgen-equivalent man (REM) or Sievert (Sv) where 1Sv = 100REM.

1 REM is estimated to cause about 300 aditional cases of cancer per million persons ( one third of which are fatal).

360 mREM Average annual exposure to radiation

10-40 mREM A CXR

18-40 REM A CT scan of the head

1.25 REM Each slice of CT scan

10-20 REM An angiogram

5 mREM A transcontinental airline flight

Radiation dose comparison,according to the FDA

More than 19,500 CT scans are performed every day in the United States; these expose each patient to the equivalent of 30 to 442 chest radiographs per scan.

An estimated 72 million CT scans were performed in the United States in 2007.

researchers estimated future cancer risks from current CT scan use in the United States, and projected that 29,000 future cancers will be directly attributable to CT scans that were performed in 2007.

No. of estimated cancer cases due to CT

14,000 abdomen and pelvis

4100 Chest

4000 Head

2700 CT coronary aniography

The US Food and Drug Administration (FDA) estimates that a CT examination with an effective dose of 10 millisieverts (1Sv=100REM), for example, 1 CT examination of the abdomen, may be associated with an increase in the possibility of fatal cancer of approximately 1 chance in 2000.

The comparison of organ-specific doses showed that CT coronary angiogram delivers a dose to the breast that is equivalent to approximately 15 mammography screenings. It also delivers a radiation dose to the lung that is equivalent to 711 chest x-rays, the authors note.

The risk is higher in children and females

Based on the highest effective dose that was observed, a 20-year-old women who received a CT scan for suspected pulmonary embolism, a CT coronary angiography, or a multiphase abdomen and pelvis CT scan could have an associated increased risk of developing cancer of as high as 1 in 80, note the authors.

"The risks declined substantially with age and were lower for men, so radiation-associated cancer risks are of particular concern for the younger, female patient.

What is becoming clear . . . is that the large doses of radiation from such scans will translate, statistically, into additional cancers.

Thank You…