Medical radiation workers see reduction in cancer risk

[John Jacobus <crispy_bird@YAHOO.COM>]

I saw this through another list server and thought it

would be of interest.

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Medical radiation workers see reduction in cancer risk

9/21/04

By: Shalmali Pal



Thanks to stringent radiation protection policies, the

cancer risk for modern imaging professionals has been

significantly reduced. Unfortunately, the same cannot

be said for their predecessors, who showed markedly

higher rates of disease, according to a meta-analysis

in the journal Radiology.

Shinji Yoshinaga, Ph.D., and colleagues from Japan and

the U.S. reviewed previously published epidemiologic

data on cancer risks in more than 270,000

international radiologists and technologists.



While close attention should be paid to the risk posed

to patients from localized, high radiation doses, the

detrimental effects of worker exposure to low doses

over the whole body should not be neglected, said

Yoshinaga, who is from the National Cancer Institute

(NCI) in Bethesda, MD, and the National Institute for

Radiological Sciences in Chiba, Japan. Yoshinaga's

co-authors are also from the NCI.



The authors compiled data from eight studies conducted

in the U.S., the U.K., Denmark, China, Japan, and

Canada between 1920 and 1998.



"These cohorts represent a valuable source of

information obtained from a large number of people who

worked over several decades during which modern

radiology and radiologic protection evolved," they

wrote (Radiology, September 16, 2004).



The authors parsed the earlier studies for the

standardized mortality ratio (SMR), or the ratio of

the number of deaths, and the standardized incidence

ratio (SIR), which is the ratio of the number of

incident cases. The specific disease processes they

examined included leukemia, melanoma, and breast

cancer.



Their two main findings were as follows: Increased

mortality due to leukemia was found among radiology

professionals who worked before 1950, when recommended

radiation doses started at a high of 30 Gy per year,

before dropping to 0.3 Sv per year, and then down to

0.1 Sv per year.



The SMR/SIR was 1.75-2.29 for leukemia found in U.S.

radiologists, Japanese technologists, and male Chinese

x-ray workers. From 1920-1939, the SMR was 1.38 for

all cancers in U.S. radiologists versus other

physician specialties.



For women workers employed between 1940 and 1949, the

relative risk for breast cancer was elevated (2.17),

especially if they'd been exposed to radiation for one

to four years. The authors noted a particular trend

among pre-1950 Canadian radiation workers: Melanoma

was limited to dental workers, who may have held

bitewing film in patients' mouths during x-ray,

resulting in high exposure to their hands.



Second, lower exposure levels were recorded after

1957, when the International Commission on

Radiological Protection (ICRP) reduced the suggested

dose limit to 0.05 Sv per year. In 1990, the

commission revamped that policy to an occupational

dose limit of an average of 0.02 Sv per year, over

five years, and not to exceed an annual dose of 0.05

Sv in a single year.



After 1950, the SMR for all types of cancer was less

than 1. In addition to better dose parameters, a trend

known as the "healthy-worker effect" may have

contributed to the reduction as these professionals

tend to lead healthier lifestyles and have better

access to medical care, the authors stated.



"We found no clear evidence of cancer risk in any of

the latest subcohorts of radiologists or

technologists," the group concluded. "While safe

radiation practices currently are an assumed part of

medical radiation work ... it is important to continue

follow-up."



Future research should include data on individual

doses to radiation workers, which would allow for a

direct comparison of risk between high-dose and

low-dose settings. In addition, the authors cautioned

that workers from 1960-1982 have yet to enter the time

period when background cancer risk is increased.

Radiation protection practices will require updates

based on exposure levels of new radiologic procedures.



By Shalmali Pal

AuntMinnie.com staff writer

September 21, 2004





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+++++++++++++++++++

"A devotee of Truth may not do anything in deference to convention.  He must always hold himself open to correction, and whenever he discovers himself to be wrong he must confess it at all costs and atone for it."

Monhandas K. Gandhi, in "Autobiography"



-- John

John Jacobus, MS

Certified Health Physicist

e-mail:  crispy_bird@yahoo.com





		

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