Radiation shielding of X-ray rooms in health care and veterinary practice
Radiation is produced momentarily during X-ray imaging. Typically, X-ray images are taken in a separate imaging room, which is designed so that practically no radiation leaves the room. Therefore, the risks caused by X-ray radiation to workers and members of the public can be typically kept to a very low level.
Premises where radiation sources are used have to be planned and implemented in such a way that the occupational exposure and public exposure is as low as possible when reasonable actions are implemented. Exposure shall, at least, not exceed the dose constraint set for the applicable group of persons, which is typically 0.1 millisieverts (mSv) per year for members of the public and 0.3 mSv per year for occupational exposure outside the premises of use. Radiation shielding is implemented by using a material in the shielding that reduces the radiation dose rate. When assessing the need for radiation shielding, the following factors could be taken into account:
- the type of equipment or radiation source and the characteristics of the radiation used
- the workload of the equipment or radiation source
- the direction and size of the radiation beam
- the location of the equipment or source in the room
- the intended purpose of the space behind the shields.
Structural shielding is often implemented by using lead, which is why the need for shielding is presented in millimetres of lead (mmPb). However, it is often more practical to implement structural shielding with other building materials, especially in the case of sources that produce lower radiation exposure. For this purpose, lead equivalent values for different radiation energies have been determined for different building materials.
The level of radiation shielding of the room’s doors and windows, including their frames, must be equal to that required from the surrounding wall. Attention should also be paid to larger penetrations, such as ventilation ducts. Particular attention has to be especially paid if people can occupy spaces behind them.
Below are some examples of the required shielding in veterinary X-ray practice when the dose constraint for the practices is set to 300 microsieverts (µSv) per year. Typically, the members of the public occupying the shielded area change frequently, which is why the need for shielding depends on the dose constraint for occupational exposure.
The number of images here refers to individual exposures, not entire examinations. For example, if, on average, two images per examination are taken with an X-ray device and the number of examinations is 10 per week, the need for shielding should be assessed on the basis of 20 images.
Intraoral X-ray units
The need for shielding, when the radiation beam is always aligned downwards, the device is positioned at a distance of 1 or 2 m from the shielded space and the imaging voltage is assumed to be 70 kilovolts (kV), the imaging current 8 milliamperes (mA) and the exposure time 0.4 s.
| Number of images per week | Need for shielding, distance 1 m (mmPb) |
Need for shielding, distance 2 m (mmPb) |
| 10 | 0.0 | 0.0 |
| 20 | 0.0 | 0.0 |
| 50 | 0.10 | 0.0 |
| 100 | 0.15 | 0.0 |
| 150 | 0.20 | 0.05 |
| 200 | 0.20 | 0.10 |
Conventional X-ray equipment
The need for shielding, when the radiation beam is always aligned downwards, the device is positioned at a distance of 1 or 2 m from the shielded space and the imaging voltage is assumed to be 70 kV and the tube current-time product 16 mAs.
| Number of images per week | Need for shielding, distance 1 m (mmPb) |
Need for shielding, distance 2 m (mmPb) |
| 10 | 0.20 | 0.10 |
| 20 | 0.25 | 0.10 |
| 50 | 0.30 | 0.20 |
| 100 | 0.40 | 0.25 |
| 150 | 0.45 | 0.30 |
| 200 | 0.50 | 0.35 |
CT-equipment
The shielding of premises in which fixed CT-equipment are used has to be determined with calculations when the floor area of the room is small and the equipment is located close to a wall or the control room. The shielding must also be determined with calculations if the workload of the device is unusually high. In other cases, structures with a lead equivalent value of 3 mm are typically sufficient.
Below are some examples of the required shielding in dental X-ray practice when the dose limit for the practices is set to 300 µSv per year as dictated by the dose constraint for occupational exposure. Typically, the members of the public occupying the shielded area change frequently, which is why the need for shielding depends on the dose constraint for occupational exposure.
The number of images here refers to individual exposures, not entire examinations, which may include multiple exposures.
Intraoral X-ray units
The need for shielding in the direction of the primary beam, when the voltage of the X-ray tube is 70 kV, the device is positioned at a distance of 2 m from the shielded space and the imaging current is assumed to be 8 mA and the exposure time 0,2 s.
| Number of images per week | Need for shielding, distance 2 m (mmPb) |
| 10 | 0.20 |
| 20 | 0.35 |
| 50 | 0.45 |
Panoramic tomography equipment
The need for shielding when the imaging voltage is 85 kV, the device is positioned at a distance of 1 or 2 m from the shielded space and the imaging current is assumed to be 8 mA and the exposure time 18 s.
| Number of images per week | Need for shielding, distance 1 m (mmPb) |
Need for shielding, distance 2 m (mmPb) |
| 10 | 0.40 | 0.05 |
| 20 | 0.65 | 0.25 |
| 40 | 0.80 | 0.45 |
Cone beam computed tomography (CBCT) equipment
The intended use of a CBCT device and the resulting exposure to the patient and the surroundings of the device can vary greatly. The lowest patient exposures from CBCT examinations equal those of panoramic tomography examinations, in which case the values above can be applied. The maximum exposure levels are several times higher than in panoramic tomography examinations. Typically, shielding that equals 1 mmPb is sufficient for all uses of a CBCT device.
Conventional X-ray appliances
Typically, shielding that equals 2 mmPb is sufficient for the walls. In directions subjected to high levels of direct primary radiation, shielding that corresponds to 3 mmPb might be needed. If the radiation-attenuating effect of the detector and other structures can be verified, it can be taken into account and no higher shielding level is needed in the direction of primary radiation than in other structures. On walls, the 2 mmPb shielding should extend to a height of at least 2 m.
Mammography equipment
Sufficient shielding for mammography equipment is typically 0.25 mmPb when the imaging voltage is less than 35 kV. If the mammography device is placed in a room with walls made of concrete or brick, then, as a rule, no additional shielding is needed on the walls. However, the need for additional shielding in the observation window and doors must be assessed separately.
Fixed fluoroscopic equipment and CT-scanners
The shielding of premises in which fixed fluoroscopic equipment or CT-equipment are used ought to be computationally determined in many cases when the floor area of the room is small and the equipment is located close to a wall or the control room. The shielding must also be determined computationally if the workload of the device is unusually high. In other cases, structures with a lead equivalent value of 3 mm are typically sufficient.
The table below shows alternative construction materials and their lead equivalents.
| Tube voltage (kV) |
<35 |
<70 |
<100 |
<150 (determined at 125 kV) |
||||
| Lead value (mm) |
0.25 |
0.25 |
0.35 |
0.5 |
1 |
1.0 |
2.0 |
3.0 |
| Construction material, (density (g/cm3))
|
Material thickness corresponding to the lead value (mm)
|
|||||||
| Concrete (2.37) |
20 |
25 |
35 |
50 |
80 |
90 |
160 |
230 |
| Brick, solid (1.65) |
|
40 |
50 |
70 |
100 |
130 |
220 |
300 |
| Steel (7.4) |
1 |
1.5 |
2 |
3.0 |
7.0 |
10 |
20 |
30 |
| Glass (2.56) |
25 | 35 | 45 | 60 | 90 | 110 | 190 | 230 |
| Plasterboard (0.75) | 55 | 80 | 100 | 150 | 240 | 320 | ||
| Wood (0.55) | 350 | 350 | 500 | 600 | ||||
One option for a construction material is plasterboard containing barium, which is sold under different brand names. The composition of this board might vary depending on the manufacturer, which is why their lead equivalents should be verified from the manufacturer's documentation.
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