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Shielding plan

A shielding plan details the level of shielding installed to protect workers and members of the public. This could include dental, veterinary, chiropractic, or other medical premises where ionising radiation apparatus is used. The plan includes floor plans, estimated dose calculations and other details related to radiation protection.

Radiation shielding must be documented when registering a radiation source and if shielding modifications are made after registering a source.

Any source installed in new or renovated premises must have a radiation shielding plan submitted with the registration application. If a replacement source is installed on existing premises which have not been renovated, submitting a copy of your existing shielding may be sufficient.

Shielding construction

The shielding plan should be submitted before construction. The shielding needs to be inspected by the Health Protection Service, or an accredited tester, during the construction phase before it is covered by paint, plaster, floor coverings or other fittings.

Any penetrations to the shielding, including cables, power points, water pipes or light switches, need to be addressed with material equal to or greater than the lead equivalence of the material which was removed.

The additional material needs to extend beyond the edges of the penetration by at least twice the distance between the original material and the additional material. If the location of a stud or nogging makes this impossible the additional material must return along the stud or nogging to meet the original layer of material.

Third party verification of installed shielding may be requested by HPS when assessing a source registration application or renewal.

Design constraints

The following design constraints should be used in radiation shielding calculations:

  • Controlled areas 2mSv/yr (40µSv/wk)
  • Other areas 0.5mSv/yr (10µSv/wk)

A controlled area limits access for radiation protection purposes. Anyone exposed to radiation is under the supervision of an individual in charge of radiation protection. In a controlled area, employees are required to follow procedures aimed at controlling or monitoring exposure.

If a blanket design constraint is used for an entire practice or department then this should be 0.5mSv/yr (10µSv/wk).

Shielding design height requirements from finished floor level are:

  • No less than 2.1m for general radiography, fluoroscopy, mammography, BMD/DEXA, OPG, intraoral, dental CBCT and nuclear medicine.
  • No less than 2.7m or to the upper slab, whichever is the lower for CT, including SPECT/CT, PET/CT and all other non-dental CBCT unless a lower height has been authorised by the Health Protection Service.

Shielding design depends on site-specific factors for high dose areas including CT and interventional radiology.

Shielding designers are asked to refer to authoritative texts, such as Radiation Shielding for Diagnostic Radiology, Second Edition for more information and to specify height requirements greater than those indicated above, where applicable.

Dental shielding design

The British Institute of Radiology design methodology, outlined in Radiation Shielding for Diagnostic Radiology, Second Edition must be used in radiation shielding calculations for intraoral, OPG and CBCT units in the ACT, along with the design constraints of 40µSv/wk for controlled areas and 10µSv/wk for other areas.

For OPG, the required incident air kerma at 1m from the patient is 1µGy per dental image. Variations from this requirement may be considered if sufficient evidence is provided to justify the variation.

For CBCT, the incident air kerma at 1m varies with the type of unit and the operating kV. Similarly, the amount of shielding is critically dependant on the kV used. Shielding experts are required to comply with the BIR methodology outlined in Radiation Shielding for Diagnostic Radiology, Second Edition. The incident air kerma at 1m may be provided by the manufacturer or may need to be determined by measurement.

Plasterboard densities

For radiation shielding purposes the density of gypsum plasterboard is assumed to be 0.705g/cm3, as determined by Radiation Shielding for Diagnostic Radiology, Second Edition.

Since plasterboard products with a density lower than this are available on the Australian market, calculation of a density scaling factor is required for any shielding design which specifies a thickness of plasterboard to achieve a particular level of x-ray attenuation.

If the specific plasterboard product which will be used is not known, then the lowest density plasterboard should be assumed for calculation of the scaling factor (currently approximately 0.57g/cm3 which gives a scaling factor of 0.81).

The calculated plasterboard thickness should be divided by the scaling factor to produce an adjusted thickness which takes account of a lower density plasterboard material.

In the absence of a published and peer-reviewed scientific paper, or data from a NATA accredited measurement facility, indicating the X-ray attenuation properties of the particular material at clinically relevant kVp values, plasterboard with a higher density will be assumed to provide only the X‑ray attenuation properties of the ‘standard’ density (0.705g/cm3) material.

Alternative shielding materials

Fyrchek plasterboard

We may request supporting information in relation to the x-ray attenuation properties of Fyrchek plasterboard if this material is included in your shielding plan.

The supporting information must be in the form of a published and peer-reviewed scientific paper that details the use of relevant thicknesses of this material at various kVp values.

Recommended information

For further information contact the Health Protection Service, and consult the following documents: