X-Ray Equipment and Safety Specifications

Study Notes

The attenuation curve displays percentage transmission of 70 kVp X-rays against added filtration (mm Al).
The graph shows a significant drop in transmission, then a slower decline as filtration increases.
The Half Value Layer (HVL) is approximately 2.65 mm Al.

For X-ray equipment up to 125 kVp, the control panel can be located within the X-ray room.
The AERB (Atomic Energy Regulatory Board) recommends maintaining a minimum 3-meter distance between the control panel and X-ray unit/chest stand for general purpose fixed X-ray equipment.

In mobile radiography, where there's no fixed control booth, the technologist should maintain a minimum 2-meter distance from the patient, X-ray tube, and primary beam during exposure.
The ICRP (1982) and NCRP (1989a) guidelines recommend a minimum 2-meter long exposure cord for mobile radiographic units.

Shielding materials like concrete and lead attenuate radiation by reducing its intensity.
These materials are placed between the radiation source and the exposed individual.

Lead is a good shielding material due to its high atomic number (82).
The mass absorption coefficient for photoelectric process increases with the cube of the atomic number (z³).

0.25 mm of lead attenuates 66% of the beam at 75 kVp.
1 mm of lead attenuates 99% of the beam at the same kVp.
For general purpose radiography, the minimum lead equivalent thickness in protective apparel is 0.5 mm.
Lead aprons cut exposure by a factor of 20.
0.25 mm Pb eq and 0.5 mm Pb eq refer to lead equivalent thickness.

X-ray tube shielding (Source Shielding). X-ray tube housings are lined with lead to protect from leakage radiation. Manufacturers are required to ensure leakage at a rate of 0.1 R/hr at 1 meter from the anode.
Room shielding (Structural Shielding). Lead-lined walls protect individuals outside the X-ray rooms from unwanted radiation.
- There are two types of protective barriers:
  - Primary Barrier: This barrier is the first to directly receive the X-ray beam.
  - Secondary Barrier: This barrier receives scattered or leakage radiation.
Control Area: shielding should allow for radiation workers receiving an occupational dose to be below <26mSv/kg/week.
Uncontrolled area: shielding should reduce exposure rates to <2.6mSv/kg/week.
Room size: X-ray examination rooms and patient waiting rooms need minimum 18 m² space.
Room walls: In residential complexes, primary beam receiving walls need 35 cm of brick or equivalent thickness. Scattered ray receiving walls need 23 cm of brick or equivalent thickness.
Openings, shielded or not: Unshielded openings for ventilation or natural light should be at least 2 meters off the ground.
Room positioning: rooms should be as far as possible from areas of high occupancy and general traffic, areas with a high concern for radiation, and other locations that are not directly related to radiation use.

Shielding for occupational workers can be achieved by limiting time in the radiation environment.
Workers should only enter radiation areas when necessary.

Lead aprons are used by radiation workers as secondary radiation barriers for protection.
Lead apron thickness dictates level of protection. Women should use customized aprons to enclose the entire pelvis, extending below the mid-thigh.

Lead aprons should not be abused, such as dropping, piling, or improperly draping. Appropriate racks are necessary for storage while the aprons should be radiographed for damage every year.

Eye glasses with side shields, thyroid shields, and hand gloves offer additional protective cover for radiation workers. The minimum lead equivalent for these should be 0.5 mm.

Many radiology departments do not prioritize patient shielding, which is recommended.
Thyroid, breast, and gonads should be shielded, particularly in children and young adults.

CT machines account for a significant, although less than half, of the collective X-Ray dose in a radiography department.
CT scanners have scattered radiation levels which can be unsafe.
Computed Tomography Dose Index (CTDI) is used to measure dose in CT. CTDI is measured in relation to the radiation field. CTDI air denotes absorbed dose in terms of air. Dtissue is absorbed dose in relation to tissue, measured in terms of CTDI air.
Measurements are made using pencil ionization chamber or thermoluminescent dosimeter (TLD).
The floor of CT rooms can have radiation as high as 0.3 Gy/day.

Adequate shielding should be implemented for floor and roof areas depending on room location. An additional 2.5 mm of lead or 162 mm of concrete is recommended.

The highly collimated X-ray beam in CT results in a markedly non-uniform distribution of absorbed dose, so the room needs to be at least 25 m².

Only authorized users may access X-ray devices. Energized equipment must be attended at all times.
Lock the lab door when equipment is unattended.
Notify of hazard presence via signs.