Keeping Radiation Exposures to X-Ray System Operators As Low As Reasonably Achievable (ALARA) in Veterinary Clinics/Hospitals
Utah Radiation Control Rules require that registrants develop and implement a radiation safety program. One aspect of radiation safety programs are written radiation safety procedures which are available to all operators of the x-ray system(s). The following information is provided to help you in developing written radiation safety procedures for your facility.
Whenever possible, restraining devices should be used to secure the animal in place during an x-ray examination. Using restraints allows the operator to step back from the table or leave the room during the x-ray examination, thus minimizing the operator’s exposure to scatter radiation.
If it is necessary to hold an animal during an x-ray examination, care should be taken to ensure that no part of the holder’s body is in the x-ray field. In order to be reasonably sure that the holder is not in the x-ray beam, it is important that the x-ray field and the light field are properly aligned. To check the alignment of the x-ray field and the light field, place a film on the x-ray table and collimate the light field to a size smaller than the cassette. Place coins on the inside of all four sides of the light field. Make sure that the outer edge of the coin is touching the edge of the light field. Take an x-ray exposure using approximately 65 kVp and 3 to 5 mAs (100 mA and 1/20 sec). Develop the resulting film. A comparison of the location of the coins in relationship to the exposed area of the film will show you how well your x-ray field and your light field are aligned.
When an individual is in close proximity to an area in which an x-ray examination is being performed, the individual may be subject to scatter radiation. Two items which decrease scatter radiation and are under the operator’s control are collimation and the kVp (kilovolt peak).
- If a low kVp is used during an x-ray examination, the animal absorbs more of the radiation and the percentage of the primary beam which is scattered is minimized. However, care must be taken to ensure that with the chosen kVp a good quality diagnostic radiograph will be produced. If the kVp chosen is too low and the x-ray examination must be repeated, the intent of reducing the kVp will be defeated because the operator will be expose to scatter radiation twice. As a side benefit lower kVp’s provide more contrast.
- It has also been shown that for smaller radiation fields less scatter radiation is present. For example, an 8 X 10 film size results in less scatter radiation than a 10 X 12 film size. If the area of clinical interest is smaller than the film size, the operator should collimate to the area of clinical interest only. Again, care must be taken not to over collimate in order to eliminate the possibility of a retake. As a side benefit, collimating to smaller field sizes reduces the scatter radiation received by the film thus increasing the film’s clarity.
Individuals which may be in the room during an x-ray examination must be properly protected from the primary beam and scatter radiation. These individuals must be instructed in the proper use of lead aprons, lead gloves, and any other protective apparel provided by the registrant.
When individuals must hold an animal or be in the x-ray room, they should stand as far away from the x-ray beam as possible. The further the individual is away from the x-ray beam, the less exposure they will receive from scatter radiation.
Personnel Monitors (Film Badges)
If an individual is likely to receive 500 mrem in a calendar year, that individual is required to be badged. If a survey is conducted based on the registrants workload and it is determined that individuals are not likely to exceed the 500 mrem, personnel monitoring of the individual is not required. However, it is recommended that any individual which is required to be in an x-ray room during an examination be provided with and instructed in the proper use of a film badge or thermoluminescent dosimeter. Personnel monitors must be worn at the collar and on the outside of the lead apron.
It is important that personnel monitors be properly stored. The control badge which is provide should be stored in an area free from possible exposure to machine generated radiation. This badge is used to monitor the amount of radiation received by all of the badges due to natural radiation and radiation received by the badges during transit. The control badge is read by the supplying company and the result is subtracted from the radiation levels obtained when each individuals personnel monitor is read.
It is also important to store each individual’s personnel monitor in an area free from machine generated radiation. The personnel monitor is to be used by only one individual and should not be exposed to generated radiation when not being worn by that individual. Personnel monitoring results are assigned to the individual assigned the badge. If the badge is stored in the x-ray room any level of scatter radiation the badge receives will be read and assigned to the individual even though the individual was not exposed to that radiation.
If you have any questions or require further assistance in developing written radiation safety procedures, please contact the DWMRC at (801) 536-0200.