radiation safety

 
 

Gamma rays, like x-rays are a form of ionising radiation, which can cause teratogenic and carcinogenic effects through their interaction with DNA.  There is no “safe” dose of ionising radiation, but there are thresholds below which adverse events are extremely unlikely to occur.  The measures described below are designed to keep radiation doses to patients as low as reasonably achievable (a concept abbreviated to “ALARA” in the radiation protection world) and to keep staff doses well below safety thresholds that are defined by the Radiological Protection Institute of Ireland.


 

protecting patients and staff

Radiation safety is achieved through a combination of education, procedures and devices, some of which are pictured above

Protecting patients


  1. All imaging procedures which use radiation require a careful balance between minimising the dose to the patient and obtaining sufficient data for the examination to be diagnostically useful.  Therefore we use a defined dose, measured in megabequerels (MBq), for each type of procedure.  Whilst it would be theoretically desirable for many procedures, It is not practical to have an infinitely variable dose that depends on the size of the patient.  Instead, for certain procedures, a fixed higher dose of radioactivity might be given for patients over a certain weight.  This is to try to ensure that enough counts are obtained for the resulting image to be diagnostically useful.

  2. Once the tracer is injected, the duration for which the patent remains radioactive depends on the physical and biological half-life of the tracer.  The physical half-life obviously cannot be changed, but biological half-life, which depends on the rate of excretion of the tracer, can be influenced.  For example, Tc--99m HMDP, used for bone scans, is excreted in the urine, so patients are encouraged to drink plenty of fluids and to void frequently to reduce their radiation dose.

  3. Radiation exposure to a fetus or a small child is more dangerous than to an adult.  Therefore great care is taken to avoid unnecessary exposure of a pregnant woman to radiation, either by direct injection of a pregnant patient or by passive irradiation of a pregnant woman by a radioactive patient.  All patients are given instructions to avoid close contact with t pregnant woman for 24 hours

STAFF SAFETY


The main tenets of staff safety are maximisation of distance from radiation and minimisation of the time spent in contact with radiation.  Dose rates from a patient injected with typical doses of Tc-99m labelled tracers are low, so it is safe for staff to be in the room with the patient who has been injected, but ideally for short times and without being too close to the patient for any prolonged period.


Staff wear radiation monitors at all times and these are processed once a month to see if staff doses are within the acceptable limits which are set by the Radiological Protection Institute of Ireland.  As well as badges worn on the body, staff who are handling radiopharmaceuticals also wear finger monitors to assess hand dose.


A detailed set of instructions, processes and workflows which are designed to ensure radiation safety, known as the “local rules” exists in every radiology department and the staff who work there need to be familiar with this document.