ESR News April 2015
Occupational doses from diagnostic and interventional radiology
John Damilakis, Professor of Medical Physics
Medical imaging procedures are performed in large numbers worldwide. Occupational radiation doses from diagnostic radiology are generally very low and well-controlled. However, fluoroscopically-guided interventional procedures are associated with relatively high patient and occupational doses, mainly due to high utilization, long fluoroscopy time and large number of cine acquisitions (1). Management of occupational radiation exposure is of great importance for radiologists and other healthcare workers involved in these examinations.
It is well known that the International Commission on Radiological Protection (ICRP) has established three radiation protection principles, i.e. justification, optimization of protection, and application of dose limits. They all apply to medical exposures of medical workers. Article 19 of the EU Basic Safety Standards on justification of practices (2) states that ‘Practices involving occupational and public exposures shall be justified as a class or type of practice, taking into account both categories of exposures’. Therefore, in the justification of medical procedures, the risk from the exposure of medical personnel participating in these procedures should also be taken into consideration. Optimization of protection is essential in order to reduce patient dose while keeping image quality at acceptable levels. Optimizing patient dose will result in a decrease in scatter radiation to the staff. The current occupational dose limits mandated in the European Basic Safety Standards are shown in the Table. It is not common for interventionalists to exceed these limits, especially if he/she takes all appropriate radiation protection measures.
Several recent studies show that the eye lens is more radiosensitive that previously estimated and thus protection of the eyes of occupationally exposed personnel is very important (3). Radiation-induced opacities and cataracts may take years or decades to develop. It is not entirely clear whether radiation-induced cataracts are stochastic or deterministic effects. However, it is known today that cataracts can occur after receiving radiation doses as low as 0.5 Gy. For this reason, ICRP has accepted the dose threshold of 0.5 Gy for radiation-induced cataracts. The equivalent dose limit for the lens of the eye for occupational exposure has been reduced from 150 mSv per yearto 20 mSv per year averaged over defined periods of 5 years, with no annual dose in a single year exceeding 50 mSv.
To decrease occupational radiation doses, exposed personnel must use protective garments i.e. a lead apron with lead equivalence of 0.25-0.5 mm to protect body trunk, leaded gloves, radio-protective glasses and a thyroid shield. Radiographers using mobile radiographic equipment should stand at least two metres from the patient. Interventional radiologists should keep their hands outside the primary beam. If hands are inside the beam, the automatic exposure control will increase exposure parameters and, therefore, radiation doses to both patient and staff will increase. Positioning the x-ray tube below the examination table will decrease radiation dose. Radiation dose to staff is reduced drastically when ceiling-suspended protective lead shielding or mobile floor shielding is used. Two dosimeters should be used, one inside the apron at the chest level and another outside the apron at the collar to monitor exposure to the eyes.
Table: Occupational dose limits (EU Basic Safety Standards, 2013)
|Dose Quantity||Occupational Dose Limit|
|20 mSv in any single year. However, in special circumstances or for certain exposure situations specified in national legislation, a higher effective dose of up to 50 mSv may be authorised by the competent authority in a single year, provided that the average annual dose over any five consecutive years, including the years for which the limit has been exceeded, does not exceed 20 mSv.|
|Equivalent dose in:|
|Lens of the eye
|20 mSv in a single year or 100 mSv in any five consecutive years subject to a maximum dose of 50 mSv in a single year, as specified in national legislation.|
|500 mSv in a year, this limit shall apply to the dose averaged over any area of 1cm², regardless of the area exposed.|
|Extremities||500 mSv in a year.|
1. Chida K etal. Occupational dose in interventional radiology procedures. AJR 2013;200:138-41
2. Council of the European Union. (2013). Council Directive 2013/59/Euratom laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom. Official Journal L-13 of 17.01.2014.
3. Ainsbury EA et al. Radiation cataractogenesis: a review of recent studies. Radiat Res 2009:172(1):1-9