Saturday, March 19, 2011

Radiation Dose and Risks (another perspective...)

Radiation Dose and Risks (another perspective...)

Radiation is measured using the unit sievert, which quantifies the amount of radiation absorbed by human tissues.

Below are some facts about the health dangers posed by higher radiation levels:

- Japan's Chief Cabinet Secretary Yukio Edano had at one point said radiation levels near the stricken plant on the northeast coast reached as high as 400 millisieverts (mSv) an hour. That figure would be would be 20 times the annual exposure for some nuclear-industry employees and uranium miners.

- People are exposed to natural radiation of 2-3 mSv a year.

- A typical chest X-ray involves exposure of about 0.02 mSv, while a dental one can be 0.01 mSv.

- Exposure to 100 mSv a year is the lowest level at which any increase in cancer risk is clearly evident. A cumulative 1,000 mSv (1 sievert) would probably cause a fatal cancer many years later in five out of every 100 persons exposed to it.

- There is evidence linking an accumulated dose of 90 mSv from two or three CT scans with an increased risk of cancer. The evidence is reasonably convincing for adults and very convincing for children.

- Large doses of radiation or acute radiation exposure destroy the central nervous system and the red and white blood cells, leaving the victim unable to fight off infections. For example, a one sievert dose (1,000 mSv) causes radiation sickness such as nausea, vomiting, hemorrhaging, but not death. A single dose of 5 sieverts would kill about half of those exposed to it within a month.

- Exposure to 350 mSv was the criterion for relocating people after the Chernobyl accident, according to the World Nuclear Association.

"Very acute radiation, like that which happened in Chernobyl and to the Japanese workers at the nuclear power station, is unlikely for the population," said Lam Ching-wan, a chemical pathologist at the University of Hong Kong.

Sources: the New England Journal of Medicine, World Nuclear Association and Taiwan's Atomic Energy Council

Plain Film X Rays
Single Radiographs Effective Dose, mrem (mSv)
Skull (PA or AP)1 3 (0.03)
Skull (lateral)1 1 (0.01)
Chest (PA)1 2 (0.02)
Chest (lateral)1 4 (0.04)
Chest (PA and lateral)5 6 (0.06)
Thoracic spine (AP)1 40 (0.4)
Thoracic spine (lateral)1 30 (0.3)
Lumbar spine (AP)1 70 (0.7)
Lumbar spine (lateral)1 30 (0.3)
Abdomen (AP)1 70 (0.7)
Abdomen6 53 (0.53)
Pelvis (AP)1 70 (0.7)
Pelvis or hips6 83 (0.83)
Bitewing dental film6 0.4 (0.004)
Limbs and joints6 6 (0.06)

Doses Received Undergoing an Entire Procedure
Complete Exams Effective Dose, mrem (mSv)
Intravenous Pyelogram (kidneys, 6 films)1 250 (2.5)
Barium swallow (24 images, 106 sec fluoroscopy)1 150 (1.5)
Barium meal (11 images, 121 sec fluoroscopy)1 300 (3.0)
Barium follow-up (4 images, 78 sec fluoroscopy)1 300 (3.0)
Barium enema (10 images, 137 sec fluoroscopy)1 700 (7.0)
CT head1 200 (2.0)
CT chest1 800 (8.0)
CT abdomen1 1,000 (10)
CT pelvis1 1,000 (10)
CT (head and chest)5 1,110 (11)
PTCA (heart study)6 750-5,700 (7.5-57)
Coronary angiogram6 460-1,580 (4.6-15.8)
Mammogram6 13 (0.13)
Lumbar spine series6 180 (1.8)
Thoracic spine series6 140 (1.4)
Cervical spine series6 27 (0.27)

Dose  MSCT Conventional angiography 
Mean effective radiation dose (mSv)  14.7 5.6

Multislice computed tomography (MSCT) using a 16-slice scanner delivers more than twice the radiation than conventional angiography

1 comment:

Winston said...

Dr Quek, I think that many specialists have a cavalier attitude in ordering CT sans for their patients.
Perhaps this is done to recover the expenses paid for these equipment.
I hope that you can put a stop to it.