The first American radiation fatality occurred in 1904 when Thomas Edison’s assistant died of cancer. Since then we have learned a lot about the harmful effects of ionizing radiation. A healthy concern about these harmful effects is understandable. However, many veterinary technicians seem to have an unreasonable fear of the harmful effects of ionizing radiation. This unhealthy concern may even affect job performance. Fortunately, these fears are generally a result of misinformation and a discussion about radiation safety with your technicians will go a long way to allay their fears. The following is a three part series that discusses the harmful effects of ionizing radiation, radiation monitoring, radiation safety, and the special cases of the pregnant veterinary technician, digital radiography, and high frequency generators.
The Harmful Effects of Ionizing Radiation:
All ionizing radiation is harmful. Ionizing radiation has the potential to cause mutations that can be passed along to future generations or mutations that result in the development of cancer. Technicians routinely ask me “how much radiation is too much or how many films can I take before I get cancer?”
The answer to these questions is a bit involved. This is because all ionizing radiation is harmful and data is not available to indicate if there is or is not a threshold below which no harmful effects will occur! In other words no one really knows just how much radiation is tolerable. (I know, so far this discussion does not bode well for allaying your technician’s fears. Hang in there.)
Scientists have been studying the problem of “how much is too much” as far back as 1931 when a group of American scientists began to look at this problem. Their group has persisted to this day at the National Council on Radiation Protection and Measurements (NCRP). This group is still considering this question and meets periodically to consider the issue. It is the NCRP that recommends a maximum permissible dose that is the cornerstone of our radiation safety policy formulated by the NCR.
Currently, the NCR guidelines state that 5000mrem (5rem) per year is the maximum permissible dose(MPD) for occupational exposure. In other words, the NCRP recommends that veterinary technicians obtain less than 5000mrem of exposure during the course of a year. However, what this really means (since all radiation is harmful and we really don’t have the data to indicate that there is a threshold below which no harmful effect will occur) is that in light of the present knowledge, this dose is not expected to cause appreciable bodily injury to a person at any time during his lifetime, but, in actual practice radiation levels should be kept as low as practical and we should not think of permissible doses as being perfectly safe.
To put things in perspective, technicians need to remember that we live in a radiation filled environment. Cosmic rays constantly bombard us from outer space, radon is present in our basements, and radionuclides in the rocks used to make our buildings and food we eat even give off radiation. On average, we can expect to get 360mrem of radiation a year just from living on earth.
A handout from the US Department of Energy called “Radiation in Perspective” can be found at the end of this article.
Understanding that 5000mrem is the MPD you can now have a meaningful discussion with your technicians and help allay their fears. To begin this discussion you will need the technician’s quarterly radiation monitoring badge reading. Technicians should be given their badge reading and this number should be related to their MPD for the quarter/year/and lifetime cumulative dose.
For example, I was recently working with a clinic where a technician saw her badge report and was terrified that she had an exposure of 28mRem for her lifetime dose. After our discussion, she understood that her MPD was 5000mrem/year so 28mrem was more than 100 times less than her exposure for a single year. Furthermore, her 28mrem was her lifetime occupational exposure. She had been working for three years. Therefore, her lifetime dose was 10,000 times less than her lifetime MPD of 5000 x 3=15,000! After our discussion, she understood that she was well below her MPD.
In most practices I evaluate, the exposure to technicians generally falls in the range of 10-20mrem per quarter. It is recommended that any technician receiving greater than 125mrem/quarter (i.e. 10% of the allowable dose) be counseled about radiation safety and safety practices enacted and enforced in the hospital to reduce the radiation exposure to the technical staff. If the technicians dose is persistently greater than 125mrem/quarter, it is likely that they are not following proper radiation safety practices or possibly that they are mishandling their badge (leaving it in the x-ray room, on the dashboard of their car etc.)
Ways to reduce radiation exposure in the veterinary hospital:
The principle guiding radiation safety in the veterinary hospital is the ALARA principle (As Low As Reasonably Achievable). It cannot be overstated that the last two words in ALARA are “reasonably achievable.” Reasonably achievable is very different from “as low as possible.” If the guiding principle was to obtain radiation exposure levels as low as possible, that would indicate a zero tolerance for radiation exposure. A goal of zero exposure would place unrealistic economic, design, and workflow constraints on the veterinary profession to the point that obtaining radiographs in a general practice would likely be impractical or cost prohibitive.
Veterinary technicians should understand that by accepting their job as a veterinary technician, they are accepting some (albeit small) risk of harmful effects of radiation exposure for the tangible benefit of gainful employment. It is the duty of the veterinary hospital owner to instruct and provide the technician with the tools necessary to obtain radiation exposures as low as reasonable achievable. These tools fall into three categories; time, distance, and shielding.
- Time:Always use the shortest exposure time possible and decrease repeats. Using a technique chart that has been customized for your practice will decrease repeats. If you do not have a technique chart, if your technique chart was not customized for your practice, or if you are having problems obtaining properly exposed radiographs, you can find a tutorial on how to create your own technique chart elsewhere on this website. Finally, digital radiography will decrease the number of repeat radiographs taken at your hospital.
- Distance:Always stay as far from the radiation source as practical. Small increases in distance will dramatically decrease exposure. If possible exit the room during radiography. The use of sedation to allow for sandbag and non-manual restraint is recommended. A tutorial about the proper use of sandbags and tape for non-manual restraint (including pictures) can be found elsewhere on this website.
- Shielding: Use proper lead shielding equipment such as lead aprons and thyroid shields. Technicians hate wearing lead shielding. Lead gloves are uncomfortable, decrease dexterity, and they smell awful. Nonetheless, technicians should be advised that not wearing gloves is not an o ption in any circumstance. Unfortunately, I have a few dozen radiographs in my database where technicians have included their unshielded fingers in the radiographs. This practice is unacce ptable for two reasons. First, these technicians should be wearing gloves. Second, human fingers should not be present in the radiograph even if they are shielded by lead!! Technicians should be instructed that lead gloves do not provide any protection from the primary x-ray beam. In other words, wearing a lead glove and putting your hand in the radiograph offers no protection at all. The lead only protects the hands from scatter radiation arising at the periphery of the radiographic image.
Special situations:
Radiation safety for the pregnant technician: The fetus is particularly susceptible to the harmful effects of ionizing radiation during the first four months of pregnancy. This special sensitivity must be considered when formulating a radiation safety protocol for the pregnant veterinary technician. The NRC states that the MPD for the pregnant patient is less than for other occupational workers. The pregnant technician should not receive more than 500mrem of exposure during the entire pregnancy and less than 50mrem in any given month.
The question that is always asked is “can my technician continue to take radiographs during pregnancy?” This is a difficult question. Legally, technicians are able to continue obtain radiographs in a veterinary hospital if the hospital follows a strict protocol for radiation monitoring and safety during the pregnancy (see below). However, a prudent approach (and an approach that nobody will criticize) is to encourage technicians to stay out of the x-ray room for the duration of the pregnancy.
Previously, it was stated that all ionizing radiation is potentially harmful and there is no threshold below which one can absolutely say for certain that that radiation exposure to the fetus is safe. This lack of scientific evidence for a threshold could be cited by a technician (or technician’s lawyer) in a legal proceeding if there was a problem associated with pregnancy. It is my opinion, that this situation simply be avoided if at all possible. However, if a technician insists on working in radiology during the pregnancy, or if working in radiology is an unavoidable requirement of employment, a strict radiation safety protocol that conforms to the NRC guidelines must be in place to protect the embryo-fetus from the harmful effects of ionizing radiation; and the veterinary hospital from liability if problems should arise related to the pregnancy.
When a technician becomes pregnant they must alert their supervisor of the pregnancy and declare the pregnancy in writing. If the technician does not declare the pregnancy in writing, the technician’s dose continues to be controlled under the normal dose limits for radiation workers.
The declared pregnant worker (DPW) should then be counseled regarding their exposure history, safety aspects of the employee’s work, the harmful effects of radiation exposure to the fetus, the proper radiation safety protocols used to protect the fetus, and provide the worker with an opportunity to ask questions. These items are outlined in the NRC regulatory guide 8.13 (Instruction concerning Prenatal Radiation Exposure). All DPW’s should be given a copy of this document. A signed copy of this document should be ke pt on record.
NOTE: Declaration of pregnancy forms, the NRC Guide 8.13, and a record of attendance at a pregnancy consultation can be found at the end of this article.
If the technician elects to continue working in radiology (which should not be a problem given the exposures commonly encountered in veterinary hospitals following prudent radiation safety procedures) the technician is given two radiation monitoring badges. One badge should be worn on the torso and the other badge should be worn over the abdomen. The badges must be submitted for evaluation on a monthly basis. Exposures must be less than 50mrem per month during the pregnancy. The monthly reports should be reviewed with the DPW and these reports should become part of the workers permanent dose history.
The fetal dose limit will remain in effect until the DPW is known to no longer be pregnant, or informs their supervisor that they are withdrawing their declaration of pregnancy.
Digital Radiography: The quality of a digital radiograph depends tremendously on the number of x-ray photons that reach the x-ray detector. In many cases, the exposure per radiograph will be increased relative to film. In our hospital, the exposure rate was increased approximately two times compared to film radiography. This increase technique will result in an increase in exposure to the technicians obtaining radiographs. However, this increase in exposure is at least partially offset by the fact that fewer repeat radiographs are taken using a digital radiography system because of the inherently wider dynamic range of digital radiography compared to film. If technicians are concerned regarding the increased exposure from working with digital radiography, they should be counseled regarding the MPD values described above. It is also recommended that heir radiation monitoring badges be reviewed with them on a monthly basis during the introduction of digital radiography to the hospital. At our hospital, we are currently evaluating if there was an increase in exposure to our technicians as a result of the introduction of digital radiography in our hospital. This page will be amended when that information becomes available.
High Frequency Generators: In recent discussions with technicians it appears that in at least two Boston veterinary hospitals, the technical staff was advised by their supervisors that they did not have to wear aprons, gloves, or thyroid shields. Both of these hospitals had recently installed new high frequency generator based x-ray machines.
Briefly, high frequency generators emit a more uniform, and relatively higher energy x-ray beam than traditional single phase generators. This results in fewer low energy x-ray photons emitted from the x-ray tube. However, this does by any means result in no scatter radiation. In fact, much of the scatter radiation is generated within the patient and is present regardless of what kind of x-ray generator is used. Therefore, lead shielding must be worn regardless of what type of x-ray generator is used in a practice.