A common misconception about the ALARA principle

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Federal regulations have been established to limit radiation exposure to safe levels and prevent the risk of long term effects of exposure (10 C.F.R. Part 20). One familiar regulatory requirement is ALARA, which stands for As Low As Is Reasonably Achievable.

The ALARA principle often gets distilled down to three concepts: time, distance and shielding. It was most likely described to you in that order and is a principle that you use everyday as a method for limiting your radiation exposure. However, it is a misconception that the order of the ALARA concept is actually in the order of effectiveness, when in reality it is reversed. In fact, adequate shielding is the most effective method for reducing exposure with distance and time being the least effective. This is a perspective deduced directly from the mathematical relationships between exposure and each of the three concepts; however, there are real-world limitations to these mathematical models and each principle has its own limitation:

Shielding: Although it provides the greatest opportunity for exposure reduction, it can only be so thick or the weight will make it very difficult to manage.

Distance: It is limited to how far you can hold a unit dosage of nuclear medicine from your body. For example, the length of your arms when holding radioactive material or facility design when trying to separate you from an injected patient may be distance limitations.

Time: You can only move so fast when injecting a dose without jeopardizing your safety and the safety of your patient. Similarly, facility design can also impact the time it takes to navigate from the hot lab to patient administration rooms.

As you know, the best implementation of the ALARA principle is to combine concepts for the more effective exposure reduction.


ALARA at work in everyday life

While the tips below aren’t novel, they are intended to serve as basic reminders to help protect you from unnecessary radiation exposure. Even if you aren’t being “benched” or your dosimeter readings are within range, the ultimate goal is to keep your radiation exposure to a minimum.

When assaying a radiopharmaceutical unit dosage:

  1. Using tongs (distance) when assaying radiopharmaceutical unit dosages will decrease exposure to your extremities.
  2. Moving the radiopharmaceutical unit dose pig closer to the dose calibrator before transferring the syringe to the dose calibrator will reduce the time the radioactive material is unshielded (time).
  3. Using both time and distance will further reduce extremity exposure.

When transporting the unit dosage to the patient:

  1. When moving the unit dosage from the hot lab to the patient room, try to use the most shielding possible. For example, if you can carry the transport shield the dosage was delivered in, the exposure will be reduced to a safe level. Once you get to the patient room, use tongs to transfer the dosage to a syringe shield for administration.
  2. When walking from the hot lab to the patient room, walk as quickly as possible (time) and hold the shielded dosage as far away from your body as possible (distance) to reduce exposure.

Visit our Online Educational Resource to learn more about nuclear medicine safety and earn continuing education credits by selecting the following courses:

  • RSP01: Radiation Safety Principles (Radiation Safety Part I)
  • RSP02: Personnel Monitoring for Radiation Exposure (Radiation Safety Part II)
  • RSP03: Surveys and Contamination Control (Radiation Safety Part III)




Disclaimer: Please consult the Occupational Safety and Health (OSHA) Act and its accompanying regulations as well as your applicable state and local laws and regulations to confirm compliance with your practice. In addition, any reader of this document is cautioned that Cardinal Health makes no representation, guarantee, or warranty, express or implied as to the accuracy and appropriateness of the information contained in this document, and will bear no responsibility or liability for the results or consequences of its use.