Radiation Exposure of Medical Staff and Radiation Protection Measures

Nuclide

Radiation type

T _1/2

E _β.max [keV]

p [%]

Eγ [keV]

p [%]

Maximum beta range in plastic [mm]

Dose rate factor^a

[mSv/hGBq]

[mSv/h]

30 cm from point source

Contact with 5 ml syringe^b

Contamination of 1 MBq in 0.05 ml droplet

Y-90

β-

2.67 days

2,284

100

–

9.2

108

–

43,500

1,350

Re-186

β-/γ

3.78 days

1,077

137

3.4

120

0.04

380

910

939

Er-169

β-

9.40 days

352

–

0.8

9.2

–

<<^c

280

344

Tc-99 m

6.01 h

120^d

141

0.3

–

0.26

354

T _1/2 half-life, E _β.max maximum beta energy, E _γ gamma energy, p emission probability

^aFirst column: skin dose rate, second column: deep tissue dose rate

^bOn 1 ml syringes, the dose rate is higher because of lower self-shielding

^cOnly very low dose rate due to bremsstrahlung

^dInternal conversion electrons

Obviously, as can be derived from the last three columns of the table, the dose rate factors (dose rate per unit of activity) and, thus, the hazard of skin exposure of staff members are much higher for beta particles than for gammas and also depends strongly on the maximum beta energy.

In situations of low radiation protection standards, the medical staff may receive high exposures (mainly to the skin on their hands) that might exceed the annual skin dose limit of 500 mSv [2]. Therefore, appropriate safety standards have to be strictly complied with.

8.2 General Radiation Protection Principles

Radiation protection is based on three rationales: justification, limitation and optimisation. These principles are defined and elucidated in numerous international recommendations (e.g. IAEA 1996 [3]) and national regulations. Particularly, the International Commission on Radiological Protection (ICRP) has addressed the nuclear medical community with several publications focusing on radiation protection of staff and patients in general and nuclear medicine [4–8]. In addition, the International Atomic Energy Agency (IAEA) has issued some comprehensive publications on this topic [9–11]. In the European Union, the basic safety standards for protection against the dangers arising from exposure to ionising radiation were implemented in the Council Directive 2013/59/Euratom (2013) [12].

8.2.1 Justification

A general definition of the justification principle is given in the European basic safety standards: “Medical exposure shall show a sufficient net benefit, weighing the total potential diagnostic or therapeutic benefits it produces, including the direct benefits to health of an individual and the benefits to society, against the individual detriment that the exposure might cause, taking into account the efficacy, benefits and risks of available alternative techniques having the same objective but involving no or less exposure to ionising radiation” [12]. In the EANM procedure guidelines for radiosynovectomy (2003) [13] and in Mödder (1995) [14], general justification criteria for RSO are given.

In the context of this article, the justification, i.e. the individual medical indication for a radionuclide therapy, is taken for granted and shall not be discussed here; however, it is a further precondition also for the justification of the occupational exposure of medical staff.

8.2.2 Limitation

The ICRP has defined dose limits for workers, which have been implemented in most countries [15].

The limit on the effective dose for occupational exposure shall be 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.

In most countries, the limit on the equivalent dose for the eye lens is still defined as 150 mSv in national legislation, but ICRP (2011) [16] and EURATOM (2013) [12] recommend 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).

In addition to the limits on effective dose, several limits on equivalent dose shall apply.

Especially in nuclear medicine, the limit on the equivalent skin dose (500 mSv per year) is of specific concern. In this case, the dose shall be averaged over an area of 1 cm², regardless of the area exposed. For keeping the limit, the area considered is that where the highest dose is suggested.

For pregnant and breastfeeding workers, the equivalent dose to the unborn child shall be as low as reasonably achievable and unlikely to exceed 1 mSv during at least the remainder of the pregnancy after pregnancy has been notified to the employer. These members of staff shall not do work which involves a significant risk of intake of radionuclides or bodily contamination.

For apprentices aged between 16 and 18 years and for students aged between 16 and 18 years who, in the course of their studies, have to work with radiation sources, the limit on their effective dose shall be 6 mSv in a year. The equivalent dose limit for the eye lens shall be 15 mSv and for the skin, for extremities, 150 mSv in a year, respectively.

For emergency situations, the occupational exposure limit shall be set, in general, below an effective dose of 100 mSv. In exceptional situations, in order to save lives, prevent severe radiation-induced health effects or prevent the development of catastrophic conditions, a reference level for the effective dose from external radiation of emergency workers may be set above 100 mSv but no higher than 500 mSv. Before they start working, the workers must be informed clearly and comprehensively about the associated health risks and the available protection measures. They undertake these actions voluntarily.

8.2.3 Optimisation

To make sure that a worker does not receive or exceed the dose limits, all procedures that may cause exposures of staff members have to be optimised regarding radiation protection. The most common rule of optimisation in radiation protection is the “ALARA principle”. The acronym refers to the principle of keeping radiation doses “as low as reasonably achievable”. In this context, economic aspects, i.e. the costs of protection measures, should be taken into account.

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