UK agency reports slight increase in radiation exposure
http://www.100md.com
《英国医生杂志》
The average annual exposure to radiation among the British public has risen slightly, according to the Health Protection Agency. Most of the increase is due to the greater number of people undergoing radiography and the increased use of computed tomography (CT) scanners, which carry higher levels or radiation than conventional radiography, it says.
Although the national average levels of radiation exposure increased only very slightly from 2002 to 2003—from 2.6 mSv to just under 2.7 mSv—radiation from medical interventions had increased by 10%, from 0.37 mSv to 0.41 mSv.
"This is due to increases in the frequency of x rays carried out and to CT scans," said Stewart Hughes, principal scientist of the waste management group in the agency抯 radiation protection division.
Taking a chest x ray picture, for example, will expose a patient to 0.02 mSv, whereas a CT scan of the chest carries a dose of 8 mSv.
But even though the levels of medical radiation have increased, such levels of exposure carry a very low risk of causing cancer. The national average exposure to radiation of 2.7 mSv gives a risk of cancer of 1 in 7400, Mr Hughes said. This compares with a one in five risk of cancer overall from all causes. Occupational workers whose exposure to radiation is monitored annually are not meant to receive more than 20 mSv.
"The radiologists who carry out these examinations must ensure that the dose is the minimum required to carry out the examination," Mr Hughes said. "They must also balance the risks according to the requirements for the examination."
Diagnostic nuclear medicine has also become more common, adding to the average exposure to radiation. However, exposure to high dose radiation as part of a treatment is not included in the statistics. "While there are risks with the exposure levels arising from therapeutic doses, it is not felt appropriate to consider these exposures in the review," the report says.
Other important sources of radiation exposure in the UK include background radon gas, which emanates from the ground and is found in higher levels in Cornwall and Devon than other parts of the UK. The annual average exposure to radon is 1.3 mSv—a level unchanged since the last review in 1999.
However, exposure to cosmic radiation has increased, as a result of more people flying, although the risk is still relatively low.
An eight hour flight from London to New York, for example, would expose passengers to 0.01 mSv of cosmic radiation. A return journey would expose them to as much radiation as from one chest x ray picture; whereas an air traveller would need to make 400 return journeys between London and New York to receive a dose of radiation equivalent to that in a CT chest scan.
Dr Paul Dubbins, vice president of the Royal College of Radiologists and dean of the Faculty of Clinical Radiology said that he welcomed the work of the agency in monitoring the level of exposure to radiation among patients.
"We note that it is important to continue to assess trends in radiation in the future. However, the royal college would stress that in most cases the potential risks which result from exposure to radiation are outweighed by the benefits of early diagnosis and treatment of an injury or disease."(Lynn Eaton)
Although the national average levels of radiation exposure increased only very slightly from 2002 to 2003—from 2.6 mSv to just under 2.7 mSv—radiation from medical interventions had increased by 10%, from 0.37 mSv to 0.41 mSv.
"This is due to increases in the frequency of x rays carried out and to CT scans," said Stewart Hughes, principal scientist of the waste management group in the agency抯 radiation protection division.
Taking a chest x ray picture, for example, will expose a patient to 0.02 mSv, whereas a CT scan of the chest carries a dose of 8 mSv.
But even though the levels of medical radiation have increased, such levels of exposure carry a very low risk of causing cancer. The national average exposure to radiation of 2.7 mSv gives a risk of cancer of 1 in 7400, Mr Hughes said. This compares with a one in five risk of cancer overall from all causes. Occupational workers whose exposure to radiation is monitored annually are not meant to receive more than 20 mSv.
"The radiologists who carry out these examinations must ensure that the dose is the minimum required to carry out the examination," Mr Hughes said. "They must also balance the risks according to the requirements for the examination."
Diagnostic nuclear medicine has also become more common, adding to the average exposure to radiation. However, exposure to high dose radiation as part of a treatment is not included in the statistics. "While there are risks with the exposure levels arising from therapeutic doses, it is not felt appropriate to consider these exposures in the review," the report says.
Other important sources of radiation exposure in the UK include background radon gas, which emanates from the ground and is found in higher levels in Cornwall and Devon than other parts of the UK. The annual average exposure to radon is 1.3 mSv—a level unchanged since the last review in 1999.
However, exposure to cosmic radiation has increased, as a result of more people flying, although the risk is still relatively low.
An eight hour flight from London to New York, for example, would expose passengers to 0.01 mSv of cosmic radiation. A return journey would expose them to as much radiation as from one chest x ray picture; whereas an air traveller would need to make 400 return journeys between London and New York to receive a dose of radiation equivalent to that in a CT chest scan.
Dr Paul Dubbins, vice president of the Royal College of Radiologists and dean of the Faculty of Clinical Radiology said that he welcomed the work of the agency in monitoring the level of exposure to radiation among patients.
"We note that it is important to continue to assess trends in radiation in the future. However, the royal college would stress that in most cases the potential risks which result from exposure to radiation are outweighed by the benefits of early diagnosis and treatment of an injury or disease."(Lynn Eaton)