Cancerous Agents Warrant Precautionary Strategies

Technological advances and practitioner compliance appear to have lessened the risk of cancer in veterinarians, although potentially carcinogenic exposures are still an unfeigned threat to the profession.

Experts says that while the risks of malignancy in veterinary medicine from radiation is no greater than that of human medicine, it���s still better to practice safety.

Evidence - what little exists specific to the veterinary profession - indicates exposure to radiation and anesthetic gases poses the biggest workplace threat to veterinarians.

Additional data are "scant" compared to other professions, such as dentistry or radiography, says Dr. Lin Fritschi, author of the paper, "Cancer in Veterinarians" (J Occup Environ Med 2000;57:289-297).

Fritschi, senior lecturer at the University of Western Australia, says because veterinarians account for just 0.03 percent of the working population in western countries, they are usually lumped with statistics of other occupations.

X-ray carcinogens

In one study of female DVM graduates from the University of California, Davis, X-ray exposure was more common in small animal practice as opposed to large animal practice. Forty-three percent of those who took X-rays reported doing so at least five times a week. When veterinarians were monitored for dose exposure, the doses were well below the maximum permissible dose of occupational exposure.

Radiation exposure risks accelerate when animals need to be restrained during procedures, and with use of poorly maintained equipment and lack of training in radiation safety.

Studies conducted from 1980 showed high incidences of poorly shielded radiographic equipment and protection measures in veterinary surgeries. In 1989 a study conducted by Ohio State University that measured radiation safety in 29 Ohio veterinary practices found not all practices comply with radiation safety guidelines.

The study showed that collimators, which narrow the X-ray beam, were not used in 14 percent of practices. Although lead aprons and gloves were commonly used, researchers found they were rarely tested. Film badges were worn by about 50 percent of practices, but some practices shared the badges among the staff. Lead lining was present in only two of the 29 practices.

Dr. Myron Bernstein of the American College of Veterinary Radiology, says circumstances have changed since 1989.

"Years ago, when veterinarians dealt with imaging, they had incidences of radiation burns, especially with fluoroscopy procedures used unwisely. Since then, ACVR has put out programs to stress safety for small animal practitioners. Today the profession is well aware of safety factors.

"Incidence of malignancy in veterinary medicine is not any greater than that in human medicine."

But it's better to practice safety than be sorry, experts agree.

How to protect

"State and national regulations are in effect regarding appropriate shielding of the room, and no one is in the room during administration of treatment," says Dr. Susan LaRue, Dipl. ACVR, associate professor in the Veterinary Teaching Hospital at Colorado State University. "The radiation dose for personnel associated with radiation therapy is much lower than for personnel associated with diagnostic radiology, where people are holding the animals and lower energy DX X-rays tend to scatter."

She says risks for secondary cancers, which typically occur years after treatment, are "low but real."

"The probability of a radiation-associated cancer has not changed, but as more animals are treated, it is more probable," says LaRue. "The risk is the same as for human patients who undergo radiation therapy."

And the guidelines are also universal for those who administer X-rays.

"Dealing with radiation, there should be really strict workplace guidelines," says Linda McCauley, Ph.D., professor at Oregon Health Sciences University and expert on occupational and environmental exposures. "There should be periodic monitoring to make sure there is no radiation leakage. If you follow the protection guidelines, the levels are supposed to be such that you don't have to worry about exposures exceeding the limits."

She recommends turning to OSHA for in-depth materials on radiation safety. "If I was a veterinarian, they'd be the first people I'd call to determine safe levels."

Fritschi also advises servicing machines regularly to have them checked for leaks.

"Make sure all staff are trained appropriately in radiological protection and that systems are in place to minimize exposure," she cautions.

The rules are simple, says Diane McKelvey, DVM, author of "Safety Handbook for Veterinary Hospital Staff."

"Don't put your hands in the primary beam. Your hands should never show up on an X-ray...wear a dosimeter to measure your exposure. Wear the lead-lined equipment."

Anesthetics

Most veterinarians perform surgeries and are acquainted with anesthetics, specifically halogenated anesthetics and nitrous oxide.

A study of private veterinary practices in Colorado showed that 81 percent of practices (90 percent of small animal; 59 percent of large animal) used inhalation anesthetics.

Exposures to halogenated anesthetics should be less than 2.0 ppm with a time-weighted average of 50 ppm, according to the National Institute for Occupational Safety and Health. Concentrations in veterinary surgeries appear to exceed the maximum limit in up to 50 percent of measurements.

For nitrous oxide, recommended exposures should be maintained at <25ppm with a TWA of 50 ppm, NIOSH reports. Again 75 percent of veterinary surgeries exceed this concentration.

Although these excess exposures stand out, Fritschi notes in her study that veterinarians in general spend less time than human anesthetists with anesthetics. The typical small animal veterinarian spends five to 20 hours a week performing surgery and in the recovery room. In comparison the mean time human anesthetists spent weekly in surgery and the recovery room was 33.2 hours.

No matter the comparisons, anesthetic exposures can be reduced considerably with the help of a scavenger, experts acknowledge.

Exposure reduction

Scavenging systems enable removal of gases exhaled by patients in operating rooms. The systems include long breathing tubes on the expiratory port to carry gases to the extraction side of the air-conditioning system.

Waste anesthetic gas scavenging is not commonly used in veterinary practices, again potentially due to cost, lack of training, et cetera.

But that's no excuse, according to McKelvey.

"You have to have a working scavenger on every machine. Everyone should know how to reduce his or her risk. And people working around anesthetics need to be trained."

The main concern with anesthetics is still for their reproductive rather than carcinogenic effects, Fritschi says. In previous studies, anesthetics have been linked to spontaneous abortions and development of congenital abnormalities in offspring.

Mortality ratios vs. incidence

Little research exists that tracks incidence of exposure to cancer; instead, studies have focused on mortality rates of death in veterinarians from lymphohematopoietic cancers, melanoma and colon cancer.

"All developed countries and many developing countries have death registries ... and so it's relatively easy to find out deaths from cancer," says Fritschi.

For cancer incidences, researchers would need a cancer registry that compiles cancer case data of a particular region.

By law, "some countries, such as Australia and Canada, have cancer registries which cover the whole country," Fritschi says. So, for Australia, tracing incidences of cancer is relatively easy.

"This isn't possible in most other countries," she says. "The U.S. for example has no country-wide cancer registry coverage."

The United States relies on proportional mortality ratios (PMRs).

Cancer types

Veterinarians differ only slightly from the general population for deaths from all cancers combined.

The profession is considered to be comprised of individuals of a higher socioeconomic status, reports Fritschi, and is therefore assumed to have a lower cancer mortality than the general population.

That was not the finding, however, in a case control study of multiple myeloma incidences in veterinarians. Investigators cited a slightly higher risk in veterinarians than other occupations (based on six cases out of nearly 12,000).

Veterinarians fared better in the lung cancer category, with a 30 percent less risk than other occupations, according to another study. This could be attributed to greater health knowledge, which would diminish the desire to smoke, asserts Fritschi.

But greater health knowledge does not seem to matter in melanoma cases. Self-employed and employee veterinarians had higher PMRs from melanoma than government and educator veterinarians. The risk was especially found to be higher in non-small animal veterinarians.

Fritschi says she presumes melanoma risks are greater because large animal veterinarians may be exposed to the sun more than their colleagues may be.

Fritschi's study asserts that cancer risk in veterinarians is about the same as the general population. While lung cancer risk is decreased, risk for lymphohemapoietic cancer, melanoma and colon cancer is greater, based on mortality ratios.

Risks of skin cancer, thyroid cancer and leukemia resulting from X-ray exposure are real but not on the increase for veterinarians. Risk from anesthetics is nearly negligible in this profession, according to Fritschi.

Overall, there's still diminutive risk for cancer, says safety author McKelvey.

"I think the incidences are falling as people are getting much smarter about where the hazards are and how to stay away from them. People are much more careful ... than they used to be. In the old days, veterinarians wouldn't even wear gloves and not think much about it."