What Is ALARA?

As Low As Reasonably Achievable (ALARA) is a buzzword commonly used in medical disciplines utilizing ionizing radiation for the diagnosis and treatment of disease. It is a phrase that should be considered whenever a patient, healthcare professional or a physician is in a situation where they might be exposed to radiation.  However, what does ALARA really mean in this context, where does it come from, and why is it used?  These questions will be addressed in this article from FluoroSafety and Universal Medical.

It’s all based on the LNT model

The linear-no-threshold (LNT) dose-response model describes the risk of stochastic effects following exposure to ionizing radiation, as a function of dose.  This model is based on available scientific data* from large exposed populations, such as Japanese atomic bomb survivors and is widely accepted by regulatory agencies and governments.  If the LNT model is correct, risk increases linearly with radiation dose, and there is no safe amount of radiation exposure where the increased risk is zero.  Because LNT suggests that there is no safe radiation dose, this motivates us to keep both our radiation dose, and the radiation dose that our patients receive very low.   More details on the LNT are available in the Advanced Training Program from FluoroSafety.

What is reasonable?

The use of ionizing radiation is necessary in many medical disciplines and while the LNT tells us that there is no safe level of radiation, we also understand that there are many cases where radiation must be used.  For example, before X-rays and CT scans, exploratory surgery was often utilized to diagnose unknown medical conditions.  Certainly, no patient would choose to receive exploratory surgery instead of a CT scan because they were concerned about radiation risk!  These risks must be put into perspective and the benefit weighed against the risk—for both patients and medical professionals who work around radiation.

For patients, the benefit of medical exposure to diagnose and treat disease is clear.  However, just because the patient receives a well-defined benefit, does not mean that radiation can be used indiscriminately.  The smallest amount of radiation that will allow the physician to diagnose or treat the suspected condition should be used—in other words, doses should be kept ALARA.  ALARA in diagnostic imaging may be as simple as using the lowest possible CT, X-ray or fluoroscopic technique factors.  It may also include protection devices such as lead aprons or gonadal shields to protect organs that do not need to be imaged.   Newer protection devices such as bismuth breast and eye shields can be useful for certain CT exams and can reduce dose to these sensitive tissues.

In occupationally exposed individuals, the benefit is entirely that of gainful employment.  There is no potential health benefit like there is for a patient receiving a chest X-ray to diagnose disease; therefore, risk/benefit must be adjusted accordingly.  The federal government strictly enforces dose limits for the occupationally exposed to protect this population which does not receive a well-defined benefit for their radiation exposure.  In practice, very few occupationally exposed individuals approach the federal dose limits, primarily due to their job function.  A CT technologist for instance, leaves the scanner room prior to starting the scan.  Lead shielding in the walls keeps the technologist’s dose ALARA.

However, technologists, nurses and physicians involved in fluoroscopic procedures often do not have the luxury of leaving the examination room while X-rays are being produced.  For these individuals, doses may be maintained ALARA by following the three cardinal rules of radiation protection, which are also discussed in detail in the Advanced Training Program from FluoroSafety.

Time, Distance and Shielding

In fluoroscopic procedures, occupational dose is proportional to the amount of time spent in the room when X-rays are being produced.  Staff dose can be reduced by keeping non-essential personnel out or by stepping outside when performing digital acquisition imaging or rotational CT angiography.  Power injectors are necessary in these cases and allow for both a reduction in staff dose as well is improved vascular contrast.

Another key component of keeping occupational doses ALARA is distance.   Often times the scattered radiation coming from a patient in a fluoroscopic, CT or X-ray procedure can be approximated as a point source; to this end the inverse square law applies.  Therefore, if one doubles their distance away from the source of radiation, the dose to that individual is decreased by a factor of four.  In fluoroscopy or CT procedures, it is often the case that taking one step back away from the patient will cut your dose in half.  Ancillary personnel who do not need to be near the patient can minimize their dose by maximizing their distance.

The final way to maintain doses ALARA is to use shielding whenever possible.  Personnel protective equipment consisting of lead or lead-free garments an integral component of proper radiation safety practice when working near fluoroscopy, CT or X-ray procedures.  Individuals in the room during fluoroscopy procedures should also wear protective thyroid collars and lead glasses to protect these sensitive organs.  For interventional fluoroscopy procedures, some operators find that sterile radiation reduction drapes can decrease their exposure to radiation.  Rolling and hanging glass shields provide superior protection compared to radiation reduction garments and should always be worn when commensurate with the goals of the procedure.

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Sources: 

*National Research Council. Health risks from exposure to low levels of ionizing radiation: BEIR VII—Phase 2. National Academies Press; Washington, DC: 2005.