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Thursday, May 04, 2006

Essential reading: Imaging X-rays Cause Cancer


Imaging X-rays Cause Cancer

"Let's play a new game: Its called Fry Teddy"
Go here for a PDF summary of the BEIR VII report on this most important subject.
http://fermat.nap.edu/execsumm_pdf/11340.pdf
The report was issued by the National Academy of Sciences in the fall of 2005. The National Academy of Sciences is the largest scientific body in the world. The focus of their report was the part that ionizing radiation plays in the development of cancer. The benchmark that they came up with is that an x-ray exposure of 10 mSieverts (mSv; units that radiation dose is measured in), which is roughly equivalent to the radiation a patient is exposed to with a CT study of the chest or a CT study of the abdomen, produces cancer in 1 per 1000 patients.
Read the following quotation by imaging expert Dr Richard C. Semelka, MD:
“The indisputable fact, and in my opinion rendered truly indisputable by the BEIR VII report, is that medical x-rays cause cancer. BEIR VII also emphasizes that there may be no safe lower limit.[1] This statement taken as said has the potential to cause considerable alarm, so my intuitive modification is that perhaps below the dose of a standard body CT, which is approximately 10 mSieverts (mSv; units that radiation dose is measured in), there is likely negligible if any risk for an individual test.
However, even 1 body CT scan (1 CT scan of only 1 of the following regions: the chest region, the abdominal region, or the pelvic region) carries with it some element of risk. The risk that BEIR VII reports is 1 in 1000 chance of developing cancer from a 10 mSv radiation dose. In my prior report, I described what is written on the US Food and Drug Administration Web site, which is a 1 chance in 2000 of developing cancer from a dose of 10 mSv. The BEIR VII report doubles that risk. The risk in children is even higher, with a reported chance of 1 in 550 of developing cancer.”
Read this extract carefully about what the Dr Semelka says about medical x-rays:
“In general, BEIR VII supports previously reported risk estimates for cancer and leukaemia, but the availability of new and more extensive data have strengthened confidence in these estimates. A comprehensive review of available biological and biophysical data supports a "linear-no-threshold" (LNT) risk model that the risk of cancer proceeds in a linear fashion at lower doses without a threshold and that the smallest dose has the potential to cause a small increase in risk to humans.”
Note that there is no safe lower threshold – cancer risk is linear.
The following is a table of the standard reported dose of radiation for various common imaging procedures:

Table: Average Radiation Doses Associated With Common Imaging Studies

Diagnostic Examination
Effective Dose (mSv)
X-rays
Chest (PA film)
0.02
Head
0.07
Cervical spine
0.3
Thoracic spine
1.4
Lumbar spine
1.8
Abdomen
0.53
Pelvis/hip
0.83
Limbs/joints
0.06
Upper GI
3.6
Lower GI
6.4
Screening mammogram
0.13
CT
Head
2.0
Abdomen
10.0
Chest
20-40
Pulmonary angiography
20-40
PET - CT
25
You can see from this table that many people are easily getting far too much radiation; especially from CT scans and when one takes account the number of x-ray studies that one may receive throughout a lifetime, including dental x-rays.
There is too much damaging radiation in my opinion and the experts now agree.
Patients who are receiving multiple CT scans and more x-rays from other sources are getting dosages that far exceed what would appear reasonable risk.
It is the patients and their families who end up carrying the can for the consequences. By the time any cancers rear their ugly heads, the institutions and the individuals who first ordered the radiation will probably be long gone. Who pays? Ultimately, it is the patient and their families.

Here is what Dr Semelka recommends to patients”

“I believe it is your right to know that radiation exposure from medical x-rays, in particular procedures utilizing high x-ray doses (eg, CT, PET, PET-CT), may result in cancer, and it is your right to request an alternative procedure when that alternative procedure generates comparable diagnostic information. Providers should know which alternative imaging modalities provide comparable information for the medical indication that you have. It is your right, based on the Hippocratic oath that all physicians have taken, that you undergo the safest test that has sufficient diagnostic accuracy to evaluate your condition. I recommend that you refer your provider to the BEIR VII report regarding radiation hazards, and Abdominal Pelvic MRI regarding how to perform and interpret MRI studies -- if the capabilities of MRI are questioned. Liver exams are one study in particular that should almost always be done with MRI.”
Concluding advice:
Always question the need for imaging x-rays, no matter the reason and to avoid CT scans altogether – be the imaging for a dental exam, a suspected fractured foot or to find the source of abdominal pain.
In most cases, there is a good alternative. Where there is not, insist on the lowest possible exposure in order to get the job done and always insist on a protective lead shield to protect the rest of your body from radiation scatter.

Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII-Phase 2. 2005. Available at: http://books.nap.edu/catalog/11340.html
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