PRIOR RISK ASSESSMENT FOR WORK WITH IONISING RADIATION:
In-vivo STUDIES
SCOPE AND DEFINITIONS
A generic risk assessment for routine work with small quantities of radioisotopes in laboratories has
been undertaken. This risk assessment only considers the additional radiation risks arising from in-vivo
studies (animal and human volunteer).
The activity levels used in individual studies are expected to fall within the limits specified in the generic
risk assessment e.g. 1000MBq (27mCi) of H-3, or 400MBq (11mCi) of C-14. However, there are some
differences between the generic assessment and this work that require further consideration, as follows:

The generic assessment covers very small-scale work, i.e. where the active material is confined to
a drip tray or small area of bench. In contrast, when activity is administered in vivo this degree of
local containment is not expected.

The generic assessment does not cover work that might give rise to airborne contamination. In vivo
studies present two possible means of producing airborne contamination, i.e.:

Metabolism of administered compounds could lead to exhalation of activity i.e. as tritiated water
vapour or 14CO2; and

Active formulations may initially be provided in the form of a dry powder that could be resuspended.

The studies are considered to pose some risk of injuries from sharps e.g. needles used for
intravenous injections and animal bites.
RADIATION RISKS (NORMAL OPERATIONS AND ACCIDENTS)
Dose rates and external radiation risk to individuals
External radiation risks are expected to be no greater than those considered in the generic assessment.
In fact, administered activity usually carbon-14 or tritium and external radiation doses to persons are
expected to be negligible.
Contamination levels and internal radiation risks to individuals
The activity levels used are the same, or less, than those assumed in the generic assessment.
Consequently, the level of risk from internal exposure is still expected to be minimal for the majority of in
vivo study procedures. Four additional exposure scenarios are, however, worth considering, as follows.
1.
Inhaling re-suspended dry powdered compound
This might occur if the compound was spilled or dropped prior to it being made up into solution.
To illustrate the potential radiation risk, it is assumed that 10% of the material is re-suspended
into the air. For the highest activity studies, this corresponds to an activity of approximately
2MBq. Assuming a small room volume (10 m3) and a standard inhalation rate of 1.2m3 h-1 for 1
hour gives an estimated dose (for C-14) of approximately 1mSv. This is considered a very
pessimistic estimate. It is standard practice for fume cupboards to be used when handling dry
compounds, and this precaution should be sufficient to ensure that the risk of internal exposure is
minimal.
2.
Surface contamination arising post-administration
Materials such as excreta, blood and autopsy samples, etc are essentially a source of surface
contamination. However, an inherent requirement of such studies is to collect any and all such
active material. Given the low levels of activity involved in such materials, it is considered that
the standard precautions to ensure full recovery of administered activity (plus the usual hygiene
regime) are more than sufficient to protect against contamination spread.
3.
Exhalation of metabolites
Animal studies are also designed to collect any exhaled activity. In human volunteer studies, this
should not be an issue (i.e. having been avoided through previous work on the metabolism of the
compounds in question). Some C-14 may be exhaled by volunteers after administration of
activity. In any case, the exposure of the volunteers themselves is very low; even if a fraction of
the activity administered was exhaled, doses to staff and other persons in the same room would
be expected to be negligible.
4.
Internal exposures from accidents involving sharps/bites
The highest possible intake from such incidents is assumed to be as a result of an inadvertent
needle-stick injury from a syringe about to be used to administer the initial activity. Even being
very pessimistic, it is estimated that the maximum activity that could accidentally be injected into
a person is of the order of 1MBq (30μCi). For the radionuclides commonly used this equates to
an internal dose of well below 1mSv.
Precautions are already in place against sharps and bite injuries e.g. due to possible biological
hazards and these are considered sufficient to ensure that the risk of internal exposure is
negligible.
RECOMMENDED ACTIONS (Ionising Radiations Regulations 1999)
Note: All the relevant precautions arising out of the generic risk assessment for routine work with small
quantities radioisotopes should be considered to also apply to in-vivo studies. This section lists the
additional precautions considered necessary.
Restriction of exposure
No additional precautions are considered necessary. The normal precautions observed in studies are
considered more than sufficient to ensure that radiation exposures to staff and other persons will be
negligible. These precautions include:

The use of a fume cupboard when handling dry active compounds prior to the addition of the
vehicle liquid.

Routine measures to ensure the collection of excreta and other active biological samples
including, where appropriate, exhaled activity from animals.

Standard precautions against sharps injuries and animal bites.
Designated Areas and restrictions on access
It is concluded that special working procedures are not required to restrict exposures. Consequently,
the designation of a radiation “supervised area” is recommended, in common with all other routine
radioisotope work.
No special restrictions on access are required.
Classified persons and individual monitoring
Not required.
Workplace monitoring
Monthly surveys in all relevant areas, as per generic assessment.