The Design of Diagnostic Medical Facilities where ... - ResearchGate

Records should be kept as they will be required in years to come. Records to be kept include:
• Final approved shielding drawings and the assumptions on which the shielding recommendations were
based.
• Construction or ‘as built’ documents certifying the shielding installed.
• Survey reports.
• Information regarding alterations.
• Subsequent survey reports following changes.
A similar process is required to ensure best practice in radiation protection when an existing building is
refitted to allow for new clinical facilities, which include radiological or nuclear medicine services. This applies
even where the building is presently used for such purposes. Some of the steps may be combined in practice,
and may not be necessary if little change to the existing building structure proves necessary after a risk
assessment; however the RPA must be involved. In practice it will be essential to have detailed information
on the construction and materials in the existing walls, floors, ceilings, etc., in order to determine if additional
shielding is required.
2.4 Dose limits and dose constraints
To protect workers and members of the public from the hazards of exposure to ionising radiation dose limits
for 12 month periods are set down in S.I. No. 125 of 2000. These dose limits are presented in Appendix A
and are enforced by regulatory control. In brief they require that occupationally exposed workers receive less
than 20 mSv per year and that members of the public receive less than 1 mSv per year. These limits can be
taken as the lower boundary for unacceptable risk.
When designing new facilities the design should be to a standard that will keep the doses to workers and
members of the public as low as reasonably achievable (the ALARA principle) taking social and economic
factors into consideration. This means that the facility should be designed to ensure that the radiation
exposure of workers and members of the public are much lower than those of the legal dose limits. To ensure
that optimisation of protection exists, dose constraints are applied to the design of any new facilities.
A dose constraint is defined by S.I. No. 125 of 2000 and S.I. No. 478 of 2002 as “a restriction on the
prospective doses to individuals, which may result from a defined source, for use at the planning stage in
radiation protection whenever optimisation is involved”. They are generally regarded as advisory. Thus the
dose constraint, while not having the legal force of a dose limit, is the value that must be used in planning
the design of a new facility.
There are other situations in which the term dose constraint is used, for example, in dealing with the exposure
of comforters and carers, and these situations should not be confused with the above.
The dose constraints to be used in the design of all new medical facilities are given in Table 2.1. It is also
prudent to use these dose constraints in situations where existing facilities are being upgraded or modified or
when new equipment is being installed in existing facilities.
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The Design of Diagnostic Medical Facilities where Ionising Radiation is used