Skin injuries to patients can be avoided when radiation dose is monitored

Radiation dose due to interventional radiology procedures has attracted the attention of specialists for the past several years. Special dedicated radiation protection appreciation programmes will be useful to make specialists aware of the need to reduce radiation doses.

K.S.Parthasarathy



Public release date: 20-Nov-2007
[ Print Article | E-mail Article | Close Window ]

Contact: Necoya Tyson
necoya@arrs.org
703-858-4304
American Roentgen Ray Society
Skin injuries to patients can be avoided when radiation dose is monitored

Maximum radiation skin dose during coronary angioplasty can be accurately determined by monitoring the total entrance skin radiation dose as the patient is being examined and dividing that number in half according to a recent study conducted by researchers at Tohoku University in Sendai, Japan. By knowing the maximum radiation skin dose, radiologists can avoid skin injury to the patient, the researchers said.

Angioplasty, is a procedure that helps treat narrowed coronary arteries. “Many patients benefit greatly from procedures such as angioplasty, however, a major disadvantage associated with these procedures is patient radiation exposure,” said Koichi Chida, PhD, lead author of the study. “In most cardiac interventional procedures, real-time monitoring of maximum skin dose is not possible,” however monitoring total entrance skin radiation dose is, Dr. Chida said. The study was conducted to determine if total entrance skin dose could help determine maximum radiation dose to the skin.

The study evaluated 194 angioplasty procedures. The researchers investigated the relation between maximum skin dose and total entrance skin dose and found that the maximum skin dose constituted between 48%-52% of the total entrance skin dose during angioplasty. There were significant correlations between maximum skin dose and total entrance skin dose during angioplasty, Dr. Chida said. .

“This study is an important addition to interventionalists’ knowledge and understanding about how to evaluate radiation exposure to their patients,” he said.

###

The full results of this study appear in a recent issue of the American Journal of Roentgenology, published by the American Roentgen Ray Society.

Minimum standards for CT colonoscopy

The American Gastroenterological Association (AGA), an Association in USA with 16,000 members has prescribed minimum standards for physicians carrying out CT colonoscopy. Specialists do not endorse CT colonoscopy to screen asymptomatic patients; it will be useful for those patients unwilling to undergo other screening tests. Let us hope that professional associations in India may arrive at similar standards for prescribing the competence of physicians carrying out this test.

K.S.Parthasarathy



Public release date: 7-Sep-2007
[ Print Article | E-mail Article | Close Window ]

Contact: Aimee Frank
media@gastro.org
301-941-2620
American Gastroenterological Association
Gastroenterology sets standards for CT colonography

Recognizing that CT colonography will play a role in screening for colorectal cancer (CRC), and the critical need to increase overall CRC screening rates, the American Gastroenterological Association (AGA) Institute issued minimum standards for gastroenterologist performance of the test. To ensure competence, a minimum of 75 endoscopically confirmed cases should be interpreted by the physician.

Despite the fact that CT colonography has not yet been endorsed as a primary screening test in asymptomatic, normal risk adults, many patients have shown interest in this test. The indications for CT colonography are controversial, with many payers recommending that this test only be indicated for patients who have had a failed optical colonoscopy or who have a mass obstructing the colon where examination of the entire colon is required prior to surgical resection. Nonetheless, CT colonography may be considered for patients unwilling to undergo other colorectal screening tests, note the authors of the standards paper, which is published in Gastroenterology, the official journal of the AGA Institute.

“Because of our specialized training, gastroenterologists are experts in CRC screening and colorectal disease. It follows that if patients want a ‘virtual colonoscopy’ it may be highly appropriate to see a qualified gastroenterologist for the test,” notes Don Rockey, MD, AGAF, chair of the AGA Institute Task Force on CT Colonography. “As CT colonography technology is evolving, it is important to check that your physician has been properly trained to ensure that the test is performed and interpreted accurately.”

After formal training, during which at least 75 tests should be interpreted, the AGA Institute Task Force on CT Colonography, which authored the standards paper, recommends that gastroenterologists should participate in a mentored CT colonography preceptorship with the candidate physically present and involved in the interpretation of at least 25-50 additional cases. In addition, it is expected that those performing CT colonography will undertake ongoing training and self assessment including attending formal continuing medical education-accredited courses in CT colonography.

The AGA Institute Task Force on CT Colonography offers the following recommendations. The full recommendations are available in the September issue of Gastroenterology.

Patient Care

* Any polyp > 6 mm in size (i.e., widest diameter) should be reported and the patient referred for consideration of endoscopic polypectomy.

* Patients with three or more polyps of any size in the setting of high diagnostic confidence should be referred for consideration of endoscopic polypectomy.

* The appropriate clinical management of patients with one to two lesions no greater than 5 mm in diameter is unknown. In the absence of data, the follow-up interval recommended for these patients should be based on individual characteristics of the patient and procedure.

Quality Control and Safety

* Practices offering CT colonography should establish a technical quality control program.

* Endoscopic results in patients referred from CT colonography to endoscopy, including true positive and false negative rates, should be tracked.

Regulatory Issues

* Split interpretations of CT colonography are feasible.

* Gastroenterologists and radiologists performing split interpretations should dictate and sign separate procedure reports that clearly state the specific services they performed related to CT colonography.

Exam and Equipment Specifications

* CT colonography should be performed using multidetector CT protocols with high spatial resolution.

* Computer workstations for dedicated CT colonography interpretation should permit 2D and 3D correlation and visualization of the colonic lumen.

* CT colonography images should be archived for later comparison.

* Primary 2D or primary 3D review of the endoluminal surface of the colon and rectum is required.

Guidelines from multiple agencies and professional societies, including the AGA Institute, underscore the importance of colorectal cancer screening for all individuals 50 years of age and older (younger for certain groups known to be at higher risk). The U.S. Preventive Services Task Force, the U.S. Multi-Specialty Task Force, and others have published recommendations for screening for colorectal cancer, the second-leading cause of cancer deaths in the United States. Currently, recommended screening tests include colonoscopy, flexible sigmoidoscopy, barium enema, and fecal occult blood tests.

The AGA Institute formed the CT Colonography Task Force to develop minimum training standards for gastroenterologists in order to provide guidance, and to ensure minimum training competencies are upheld for the performance of the exam. The AGA Institute continues to monitor CT colonography along with other potential colorectal cancer screening tests, and will continue to develop guidance tools and reports as appropriate. The AGA Institute will host a course on CT colonography for gastroenterologists on March 7-8, 2008, in Washington, DC. Additional information will be available this fall.

###

About the AGA Institute

The American Gastroenterological Association (AGA) is dedicated to the mission of advancing the science and practice of gastroenterology. Founded in 1897, the AGA is one of the oldest medical-specialty societies in the United States. Comprised of two non-profit organizations—the AGA and the AGA Institute—our more than 16,000 members include physicians and scientists who research, diagnose and treat disorders of the gastrointestinal tract and liver. The AGA, a 501(c6) organization, administers all membership and public policy activities, while the AGA Institute, a 501(c3) organization, runs the organization’s practice, research and educational programs. On a monthly basis, the AGA Institute publishes two highly respected journals, Gastroenterology and Clinical Gastroenterology and Hepatology. The organization's annual meeting is Digestive Disease Week®, which is held each May and is the largest international gathering of physicians, researchers and academics in the fields of gastroenterology, hepatology, endoscopy and gastrointestinal surgery. For more information, please visit www.gastro.org.

About Gastroenterology

Gastroenterology, the official journal of the AGA Institute, is the most prominent scientific journal in the specialty and is in the top one percent of indexed medical journals internationally. The journal publishes clinical and basic science studies of all aspects of the digestive system, including the liver and pancreas, as well as nutrition. The journal is abstracted and indexed in Biological Abstracts, CABS, Chemical Abstracts, Current Contents, Excerpta Medica, Index Medicus, Nutrition Abstracts and Science Citation Index. For more information, visit www.gastrojournal.org.

New CR technology boosts resolution, bags R&D award

Improvements in computed technology continue to attract attention.The new development is a new type of storage phosphor material based on a translucent glass-ceramic imaging plate.One of the attractions of the technology is that the image receptor can be substituted at existing equipment without changing the associated x-ray equipment.

K.S.Parthasarathy



Siemens

New CR technology boosts resolution, bags R&D award
9/3/2007
http://www.auntminnie.com/print/print.asp?sec=sup&sub=xra&pag=dis&ItemId=77337&printpage=true


By: Brian Casey

U.S. researchers have developed a new type of computed radiography (CR) technology that they believe could yield much higher resolution than existing CR systems. One prominent scientific magazine thought enough of their research to name it one of the top 100 scientific innovations for 2007.

Computed radiography has made impressive gains in achieving commercial acceptance in the last 25 years, but the fundamental technology behind CR remains the same -- photons produced by an x-ray generator are sent through a patient and captured on a storage phosphor plate that's coated with a powder that typically consists of barium fluorobromide doped with europium. The imaging plate is then taken to a laser scanner, where electrons stored in the plates are converted into light, then read out and converted into digital images.

But some industry observers believe that CR has reached a plateau in terms of improving on this basic design, and as a result its image quality has been surpassed by digital radiography (DR) units based on flat-panel technology, according to a research group that includes scientists from Argonne National Laboratory in Argonne, IL, and the State University of New York (SUNY) at Stony Brook. To improve on CR, the group developed a new type of storage phosphor material based on a translucent glass-ceramic imaging plate.

The SUNY/Argonne technology could offer much higher resolution than current CR systems, and could be used to retrofit existing x-ray rooms in the same way as CR, without requiring a new x-ray generator and other equipment, according to Anthony Lubinsky, who represented SUNY on the research team. Lubinsky is a former employee at Eastman Kodak Health Group (now Carestream Health of Rochester, NY), and has been working on CR technology for the past 20 years.

"It would be as easy to make the switch (to digital) for your x-ray room as it is with CR in the ordinary practice," Lubinsky said. "What's inside the cassette is different and what's inside the scanner box is also different, but to the user it works the same way."

See-through CR?

The heart of the new technology is a CR design developed at SUNY and Argonne National Laboratory that the group calls transparent storage phosphor (TSP). TSP is based on a photostimulable material that employs fluorozirconate rather than barium fluorobromide. Rather than coat an imaging plate with the fluorozirconate, the material is used in combination with europium-doped barium nanocrystals to create a composite glass imaging plate.
Experimental setup of x-ray imaging system for testing fluorochlorozirconate glass-ceramic imaging plates.

The SUNY/Argonne design results in a detector material that's translucent, rather than the opaque powder screen used today with CR. As a result, a point of light entering the imaging plate doesn't scatter as much as it does with conventional imaging plates, resulting in a higher modulation transfer function (MTF). That means that a manufacturer developing a CR system based on the SUNY/Argonne technology could make the imaging plate much thicker than one based on barium fluorobromide or some other type of powder, with correspondingly higher spatial resolution.

How much higher? The group has fashioned imaging plates with a resolution of 17 microns, compared with 70 microns for amorphous selenium-based DR and 100-200 microns for conventional CR, according to Jacqueline A. Johnson of Argonne National Laboratory. The group points out that the 17-micron specification was achieved in a test environment and with a radiation dose that's much higher than would be used clinically.
Phantom image collected with tabletop CR system. Parallel vertical lines represent gold bars at spatial frequencies of 19 line pairs (left) and 20 line pairs (right) per mm. All images courtesy of Argonne National Laboratory.

One of the most obvious applications for the SUNY/Argonne technology in the clinical realm would be mammography, in which CR units based on conventional technology are entering clinical use in the U.S. after the Food and Drug Administration's 2006 approval of the first CR mammography unit, from Fujifilm Medical Systems USA of Stamford, CT. Argonne's technology could give mammographers an even finer level of detail than conventional CR.

But the Argonne team believes that its technology could have a wide range of applications in medical imaging. "If it works for mammography, I would hope the resolution would be helpful in the extremities as well," Lubinsky said.

However, you won't see the SUNY/Argonne technology in a commercially available CR system anytime soon. At present, the group has built a tabletop system and collected phantom images, and their next step is to develop a working prototype. The research team estimates that it could be more than five years before the technology hits clinical users, due to the vagaries of technology development and the need to move such a system through the FDA approval process.

If the technology does make it into the commercial marketplace, it wouldn't be totally plug-and-play with existing CR systems. Although the technology could be used with existing x-ray generators and gantries, the TSP plates would require specially adapted scanners for reading the plates, according to Lubinsky.

But the SUNY/Argonne's team work was promising enough to catch the attention of R&D Magazine, which named the research one of the top 100 scientific innovations of 2007, based on the group's March 2007 paper in the Journal of the American Chemical Society (Vol. 90:3, pp. 693-698). The award will be announced in the magazine's September issue.

The development of a translucent CR imaging plate is not a new idea: "It's something that people have thought of as a great idea if you could do it," Lubinsky said. But the SUNY/Argonne group's major achievement has been in developing both a translucent imaging plate and the concept of a laser scanner to read out the images.

"The trick is to get the (TSP and readout technologies) working together so well," he said.

By Brian Casey
AuntMinnie.com staff writer
September 3, 2007

Related Reading

PACS data-mining technique tackles CR dose creep, July 30, 2007

DICOM-compliant displays aid CR/DR exposure control, July 17, 2007

CR/DR image quality: Issues and concerns, April 12, 2007

Strategies for reducing 'dose creep' in digital x-ray, April 11, 2007

Study suggests ways to cut CR radiation, March 5, 2007

Copyright © 2007 AuntMinnie.com

Ways to cut radiation dose in computed tomography

Any one who is involved in radiological protection cannot ignore the development which involves reduction in radiation doses in computed tomography (CT).CT examinations are exposing patients to doses in the range in which the survivors of atomic bombings suffered excess cancers.

K.S.Parthasarathy

Siemens

Study suggests ways to cut CR radiation
3/5/2007
http://www.auntminnie.com/print/print.asp?sec=sup&sub=xra&pag=dis&ItemId=74868&printpage=true

By: Leanne McKnoulty

A new study by Australian researchers has found that the radiation dose delivered in computed radiography (CR) examinations could be cut in half by adjusting the manufacturers recommended range (MRR) for exposure indices (EIs) by as little as 10%.

The arrival of CR has given radiographers (radiologic technologists) the ability to use a greater range of radiation exposures to produce diagnostic images, the article states. Because, unlike film-screen radiography, higher-than-appropriate exposures in CR result in better-quality images due to increased signal-to-noise ratio, and "radiographers develop a tendency to use higher than necessary exposure factors to improve image quality and avoid repeat radiographs."

To safeguard against overexposure, CR manufacturers each set their own exposure indicators -- numerical parameters that are estimates of radiation exposure on imaging plates. The feature is called EI on systems manufactured by Eastman Kodak Health Group of Rochester, NY, and sensitivity value (S) on units made by Fujifilm Medical Systems of Tokyo.

Dr. Helen Warren-Forward and colleagues at the University of Newcastle set out to explore whether radiographers were in fact producing images using EIs within the MRR. They also sought to investigate any evidence of "exposure creep," and the relationship between EIs and radiation dose using fixed and varying tube potential, in the hope that this knowledge would ensure the use of techniques that minimize radiation dose. The study was published in the British Journal of Radiology (January 2007, Vol. 80:949, pp. 26-31).

The researchers retrospectively assessed CR data for posteroanterior (PA) chest and lateral (LAT) lumbar spine imaging, from two hospitals, denoted as hospital A and hospital B, using the CR-800 and CR-850 systems (Eastman Kodak), during an 18-month period from January 2004.

The researchers selected PA chest data because, in Australian hospitals, this is the most frequently performed examination. LAT lumbar spine data were selected because the researchers felt this represented a high entrance surface dose examination. Also, these two examinations provided a contrast in exposure factors, body part, and positioning technique, they stated.

Although manufacturers of CR equipment recommend certain "exposure indicators," the researchers highlighted that higher tube potentials and lower mAs reduce patient radiation dose compared with lower tube potentials and higher mAs. "Therefore, it cannot be assumed that there is a good correlation between exposure index and patient doses," they wrote.

Using a lung/chest phantom (model CNR/R5330, Oxford Scientific, Silverwater, Australia), the researchers showed that for a fixed tube potential (125 kVp), without any change in other parameters, EI correlates with entrance-surface dose (ESD) -- there is a log relationship in dose and EI in CR. So, a small increase in EI results in a large increase in ESD. Additionally, the researchers investigated the relationship among a varied tube potential, EI, and patient dose. They found that an increasing tube potential and a decreasing mAs for a constant EI (1500) resulted in decreasing ESD.

"The results from this current study strongly suggest that EI should not be used as an indication of ESD when comparing examinations conducted between different radiographers and institutions using different tube potentials," they wrote.

The authors caution that, particularly for chest imaging, a number of factors can affect patient dose, in particular tube potential. Therefore, EI should only be used to indicate ESD for examinations within a specific department performed by the same radiographers. They found no significant variation in EIs when they compared CR imaging during normal operational hours with after-hours services.

EIs lower than the MRR, 1700-1900 for Kodak CR systems, were successfully used for 30% of LAT lumbar spine examinations at hospital B and 38% of PA chest examinations at hospital A. "This implies that the MRR may be set too high and can be reduced to values less than 1700," they wrote.

More than two-thirds of PA chest examinations performed at hospital B, but less than one-third at hospital A, were produced with EIs within the MRR. Almost half of LAT lumbar spine examinations performed at hospital B were produced with EIs within the MRR, but almost half at hospital A were above the MRR.

Using the lung/chest phantom to produce suitable diagnostic images, EIs were 1550. The researchers suggest that since a reduction in EI by 300 results in half the patient dose, reducing MRR values from 1770-1900 to 1530-1700 (a 10% reduction) would result in significant dose savings (50%).

Exposure creep was described by the researchers as a tendency by radiographers to set higher exposures than necessary, knowing that images could be manipulated with postprocessing techniques, to achieve a suitable diagnostic image.

Results demonstrated exposure creep at hospital A, where exposure indices for LAT lumbar spine CR increased 7.1% during the 18-month period. Hospital A also showed a larger range of EIs, probably due to a higher number of patients and staff, resulting in greater variation in radiographic technique, which impacts the EI levels used to produce images, the authors suggested.

The study findings highlight the need for regular staff training on the appropriate use of CR systems and departmental quality assurance programs to ensure staff adopt the ALARA principle, to keep patient doses "as low as reasonably achievable," the researchers stated. They suggested that CR manufacturers should review the acceptable range of EIs recommended.

"The results showed that an EI of 2000 produced at 125 kVp can deliver the same patient dose as an EI of 1700 produced at 70 kVp, where the EI difference of 300 represents a doubling of dose to the detector," they wrote. "EI cannot always be used as an indicator of changes to patient dose, but that a number of other factors (predominately tube potential) need to be considered."

By Leanne McNoulty
AuntMinnie.com contributing writer
March 5, 2007

Related Reading

Korean rads find no edge for high-res CR in chest exams, January 22, 2007

Study: DR delivers lower radiation dose, November 7, 2006

U.S. hospitals find ways to take the digital x-ray plunge, October 12, 2006

AuntMinnie's IMV MarketStat #44: Percentage of U.S. hospitals with DR or CR technology, October 9, 2006

Digital radiography slowly, but surely, makes its mark, July 25, 2006

Copyright © 2007 AuntMinnie.com

Informational hand out on computed tomography to parents

Since computed tomogaphy exposes patients to significant radiation doses, physicians must use them after due consideration.They must carry out CT tests only if they are clinically indicated.Children are more sensitive to radiation so use of CT for pediatric examination must receive more attention.

Dr.K.S.Parthasarathy



Contact: Necoya Lightsey
necoya@arrs.org
703-858-4304
American Roentgen Ray Society
Informational handout key to giving parents a better understanding of CT radiation risks

Simply giving parents informational handouts can improve their understanding of the potential increased risk of cancer related to pediatric CT, according to a recent study conducted by researchers from The Children’s Hospital in Denver, CO and Yale University School of Medicine in New Haven, CT.

“Like many radiology departments around the country, we are concerned about the increasing radiation exposure to children caused by increased usage of CT. When we looked into it, our emergency physicians told us that parents' expectations may play a role,” said David B. Larson, MD, lead author of the study. “The emergency room clinicians tell us anecdotally that a number of parents expect that their child will undergo CT even before the child is seen by a physician. Parents rarely seem to understand the associated risks, so we thought it might be helpful to our emergency room colleagues to provide a handout to parents to explain, in basic terms, the risks associated with CT,” said Dr. Larson.

The study consisted of 100 parents of children undergoing non-emergent CT studies who were surveyed before and after reading an informational handout that described radiation risks. Of the 100 parents surveyed, 66% believed that CT uses radiation; 99% afterwards. 13% of those surveyed before reading the handout believed CT increases the lifetime risk of cancer, versus 86% surveyed afterward.

According to the study, after reading the handout, parents became less willing to have their child undergo a CT examination if their doctor believed that either CT or observation would be equally effective. Their willingness to have their child undergo CT recommended by their doctor did not significantly change. No parent refused or requested to defer CT after reading the handout.

“While most parents knew that CT uses radiation, we were surprised to find that most parents did not realize that this radiation exposure is associated with an increased risk of cancer,” said Dr. Larson.

“While we were working on the handout, we found it extremely difficult to find meaningful estimates of exposure, dose, and risk for various types of procedures--even in the radiology literature. It is then not surprising that not only do parents underestimate the risk, but so do clinicians and radiologists,” he said. “When addressing the question of ‘how much does a CT increase the risk of cancer"” rather than providing a meaningful basis of comparison, most publications give one of two responses; either ‘the risk is slight’ or ‘it depends.’ While both may be accurate, neither are very helpful,” he said.

“Even though risk estimates are fraught with uncertainty, a reasonable quantitative estimate is an improvement upon ‘slight’,” said Dr. Larson. “If radiologists expect clinicians to have these discussions with their patients, then we need to do a better job discussing this subject amongst ourselves and with clinicians. We believe such information should be straightforward, accurate, and widely available,” he said.
###

The full results of this study appear in the August issue of the American Journal of Roentgenology, published by the American Roentgen Ray Society.

[ Back to EurekAlert! ] [ Print Article Print Article | E-mail Article | Close Window | Close Window ]

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