X rays, gamma rays, neutrons declared carcinogens

Photo: K. Pichumani

Date:31/03/2005 URL: http://www.thehindu.com/thehindu/seta/2005/03/31/stories/2005033100041500.htm Sci Tech



X-rays, gamma rays, neutrons declared carcinogens



REDUCING EXPOSURE: Medical physicists should ensure that all radiographic equipment are properly calibrated and maintained so as to provide the highest quality images at the lowest possible radiation dose.

NOW IT is official. The 11th edition of the Report on Carcinogens (ROC) released by the U.S. Department of Health and Human Services on January 31, 2005, included X and gamma-radiation and neutrons in the list of cancer-causing agents. ROC is a scientific and public health document.

It identifies potential cancer hazards. The listing does not by itself establish that a substance presents a cancer risk to an individual in daily life.

The listing for X-radiation and gamma radiation is based on sufficient evidence of carcinogenicity in humans and that for neutrons is based on the studies of their mechanisms of carcinogenesis. "X-radiation and gamma radiation are most strongly associated with leukaemia and cancers of the thyroid, breast and lung" the report asserted.

Childhood exposure

"The risk of developing these cancers, however, depends to some extent on age at the time of exposure with childhood exposure mainly responsible for increased leukaemia and thyroid cancer risks" the report cautioned.

"Exposure during reproductive years increases the risk for breast cancer, and exposure later in life increases risk for lung cancer, a press release from the National Institute of Environmental Health Sciences, National Institutes of Health noted.

Associations between radiation exposure and cancer of the salivary glands, stomach, colon, bladder, ovaries, central nervous system and skin also have been reported.

The National Toxicology Program (NTP), which prepared the report relied on the findings of sufficient evidence of carcinogenicity in humans by the International Agency for Research on Cancer as the basis for nominating X - and gamma radiation as cancer-causing agents.

Rigorous review

NTP evaluates agents of public health concern by using tools of modern toxicology and molecular biology. The rigorous review process to nominate an agent takes two and a half years.

The American College of Radiology (ACR) criticised the listing. ACR felt that many patients who desperately need X-ray examinations may avoid them.

They may mistakenly believe that they are being placed at undue risk while undergoing a medical X-ray procedure. ACR will petition NTP to have ionising radiation removed from the list.

Dr. Donald Frey, Chairman of the Board of the American Association of Physicists in Medicine (AAPM), an organisation of over 5000 medical physicists echoed similar fears. "It would be a tragedy if patients did not have needed exams because of fears raised by the report", he said.

Key role

"One of the key roles that medical physicists provide is to ensure that all radiographic equipment is properly calibrated and maintained so as to provide the highest quality images at the lowest possible radiation dose." Dr. Howard Amols, president of the AAPM noted.

Patients must ask radiologists and medical physicists about the risks and benefits of medical radiation procedures.ROC does not try to balance potential benefits of exposures to certain `carcinogens' in special situations. In a clinically indicated medical radiation procedure when carried out by qualified professionals using optimally adjusted equipment, the benefits far outweigh the risks.

Physicians routinely order many X-ray examinations. The indications are often not clinical. Repeat examinations due to poor techniques lead to unwanted X-ray dose to unsuspecting patients.

At times, even qualified professionals order exams more frequently because they cannot allow the costly equipment to remain idle! High levels of ionising radiation cause cancer. But the cancer- inducing potential of low doses of radiation is controversial.

Till we settle the issue, the radiation doses to patients should be as low as reasonably achievable (ALARA) after taking into account the clinical requirements. The listing once again highlights the importance of enforcing the ALARA principle.

K.S. Parthasarathy

ksparth@vsnl.com

© Copyright 2000 - 2005 The Hindu

Using CT for screening unjustified

Date:05/01/2006 URL: http://www.thehindu.com/thehindu/seta/2006/01/05/stories/2006010500041600.htm Sci Tech

Using CT for screening unjustified

Virtually all the scientific and professional associations think risks are not overstated

# Cardiac CT cannot detect soft plaque, the earliest form of coronary artery disease
# Each examination dose is equal to that in several hundred chest X-ray tests
# There is no outcome data available that validates its use in asymptomatic individuals


RECENTLY, A Mumbai daily published a colourful advertisement. `Know in time,' the heading splurged in bold letters, `Heart study in 8 seconds.'

According to another advertisement in another daily `Now discovering the state of your heart vessels is as quick and easy as having a cup of tea.'

The advertisements persuade a potential patient to believe that a computed tomography (CT) procedure to evaluate the heart would be beneficial. Any CT procedure is unjustified if it is not medically necessary.

Universal risk factors

As CT procedure is `non-surgical,' regular check up of the heart is possible; the first advertisement assured the reader. The centre invited patients with some universal risk factors such as `stress' and `erratic life style (long working hours, pressure and the like)' for the test.

As any city dweller may suffer from any one or more of the listed risk factors, the advertisement aims at mass screening of asymptomatic persons.

The risk factors highlighted in these ads were not identical. The coronary arteries supply blood to heart.

They may develop blockages due to formation of plaques, which consist of fat and other substances including calcium. CT can help the physician to get information on the location and extent of calcified plaque.

Specialists use CT for angiography or calcium scoring for evaluating coronary heart disease. Modern CT angiography helps to get clear images of the arteries non-invasively.

According to RadiologyInfo, a publication of the Radiological Society of North America, not all calcium deposits in the coronary arteries mean that there is a blockage, and not all blocked arteries contain calcium. Cardiac CT cannot detect soft plaque, the earliest form of coronary artery disease.

The relationship of calcium score to the likelihood of experiencing angina, myocardial infraction and sudden death remains uncertain.

"A screening application is currently not supported by the study data published. ... .I cannot recommend screening application... "

"Therefore, aggressive marketing strategies using the method in the context you described will face troublesome litigation in most countries," Professor Martin H. K. Hoffmann, Department of Diagnostic Radiology, University Hospital, Ulm, Germany, responded to an e-mail query.

In the May 25, 2005 issue of the Journal of the American Medical Association (JAMA), he described the potential of Multi Slice Computed Tomography (MSCT) to complement invasive coronary angiography.

Balancing benefit ,harm

Each CT examination exposes the patient to a dose equal to that in several hundred chest X-ray tests... "A screening application needs to balance benefit and harm"..."We therefore deem scanning only appropriate in patients with symptoms of unclear origin and high risk profile patients with positive stress test results", Dr Hoffmann cautioned.

Dr Mario J. Garcia, Department of Cardiology and Radiology, Cleveland Clinic Foundation, U.S., concurred.

Specific guidelines

"There is no outcome data available yet that validates the use of this test in asymptomatic individuals...right now we don't have specific guidelines to what should be done with a positive or negative result.

"I share the reservations of the American Heart Association, American College of Cardiology, American College of Radiology and Food and Drug Administration, we use this test primarily in symptomatic individuals with very few and justifiable exceptions." He listed the limitations of MSCT in an accompanying editorial in JAMA.

"There is, of course, much interest in cardiac screening, but I do not think the evidence yet supports widespread screening", Dr. Thomas B. Shope, Center for Devices and Radiological Health, US FDA, replied to my query.

"We continue to see similar advertisements here in the U.S., but I do not think we have as many such facilities as we did a few years ago", Dr Shope reacted to the advertisement on CT screening in the Mumbai daily.

Responding to an e-mail query, Dr Bhavin Jankharia, a Mumbai radiologist, claimed that cardiac CTs, especially in high risk patients, even if asymptomatic, can help in deciding further life style changes especially in the presence of an increased plaque burden.

Considerable controversy

"I agree that not everyone should undergo cardiac CTs, but often the choice is made by the patient," he clarified. He conceded that there is considerable controversy about self-referral and the use of screening.

"We don't encourage self referrals for many parts of the body, including chest, brain and the like. But a good number of our cardiac CT patients are self referred." He believes that the risks of radiation are over-stated.

But virtually all the scientific and professional associations think otherwise.

The professional associations dealt a body blow to commercialised CT screening in the U.S. Will it happen in India? The advertisements with unsubstantiated claims, condition the patient to go for the test.

The day is not far off when we will see a tennis/cricket player or a film star in India endorsing CT scans!

K.S. PARTHASARATHY

ksparth@yahoo.co.uk
(The author is former Secretary, Atomic Energy Regulatory Board)

© Copyright 2000 - 2006 The Hindu