Radiation Protection

Radiation Protection

Objectives

Describe dosimetry principle in calculating patients’ dose (Justification, optimization, collimation, shielding and dose reference levels) Describe radiation protective measures ( Protective gargets) Describe time, distance and shielding as protective measures Describe factors influencing patient exposure in conventional radiography

Outline

• System of radiation protection
• Personal protective equipment

Radiation Protection Measures

Factors influencing patient exposure in conventional radiography

Concepts and aims of radiation protection

Radiation Protection is a tool for the management of measures to protect health against the risks (for people and environment) generated by the use of ionizing radiation Always consider BENEFITS Vs RISKS

Biological effects of ionizing radiation: aims of radiation protection

• Deterministic effects
• RP aims at PREVENTING them.
• Stochastic effects

RP aims at REDUCING them.

Protection from what?

• Unnecessary examination or treatment (justification)

Unnecessary exposure (optimization)

Inadequate examinations, which can lead to incorrect or incomplete diagnosis (optimization)

Justification of practices

• Limitation of doses
• Optimization of protection

System of radiation protection

Justification of a practice

Justification means that any exposure produces sufficient benefit to offset the radiation harm that it might cause.

Thus, if the exposure has not any benefit it is not justified.

Optimization of protection

Optimization includes the criterion: doses should be “as low as reasonably achievable”, economic and social factors being taken into account” Optimization means that minimum risk and maximum benefits should be achieved, economic and social factors being taken into account.

BENEFIT

RISK

As Low As Reasonably Achievable

refers to the continual application of the optimization principle in the day-to-day practice.

DOSE

Limitation of doses

The normal exposure of individuals shall be restricted so that neither the total effective dose nor the total equivalent dose to relevant organs or tissues, caused by the possible combination of exposures from authorized practices, exceeds any relevant dose limit, except in special circumstances Dose limits shall not apply to medical exposures from authorized practices.

Other factors to consider in patient dosimetry

Dosimetry is the act of measuring or estimating radiation doses and assigning those doses to individuals Collimation

• Shielding

Dose Reference Levels (DRLs)

Collimation

Collimation refers to limiting the radiation field to only the necessary area for imaging.

• Reducing the size of the X-ray beam to match the patient area being imaged
• Minimizes exposure to unnecessary body parts
• Improves image quality by reducing scatter radiation

Can reduce dose by up to 80% compared to full-field exposures

Shielding

• Shielding involves using physical barriers to block or absorb radiations.
• Using lead aprons, thyroid shields, gloves, and caps for staff protection
• Placing concrete walls around radiology rooms to absorb scattered radiation
• Using lead glass for windows in control areas

Properly positioning patients and staff to avoid direct beam exposure

Dose Reference Levels

Dose reference levels provide benchmarks for acceptable doses in different imaging procedures.

• Establish diagnostic reference levels for common exams.
• Measure actual patient doses and compare to reference levels.

Use data to optimize protocols and reduce unnecessary exposure.

Personal protective equipment

Workers are provided with suitable and adequate personal protective equipment which meets any relevant regulations or standards.

Protective equipment includes lead aprons, thyroid protectors, protective eye-wear and gloves. The need for these protective devices should be established by the Radiation Protection Officer.

Protective clothing:

Gowns, aprons and thyroid protectors made of a material (such as vinyl) which contains lead Aprons should be equivalent to at least 0.25 mm Pb if the X Ray equipment operates up to 100 kV and 0.35 mm Pb if it operates above 100 kV Aprons may be of the style which is open, or contains less lead, at the back, due to the extra weight of lead required – this assumes, however, that the wearer is always facing the radiation source Gauntlets are heavy gloves. They have limited value because they are difficult to use and should therefore only be used where appropriate

Thyroid shield

Lead apron

CURTAIN

SCREEN AND GOGGLES

Protective devices

Radiation Protection Measures

• Time
• Distance

Shielding

Time

• Dose is proportional to
• the time exposed

Dose = Dose-rate x Time

Consequence

• Limiting exposure duration reduces overall dose
• The longer you're exposed, the more radiation you absorb
• Minimizing time near radiation sources is crucial

For medical procedures, reducing exam time lowers dose

Distance

• dose-rate
• Dose-rate  1/(distance)2

Inverse square law (ISL):

Consequence

• Increasing distance from the radiation source reduces exposure
• Radiation intensity decreases rapidly with distance
• The inverse square law applies – doubling distance reduces dose to 1/4
• Moving farther away provides significant dose reduction

For medical imaging, positioning patients farther from detectors reduces dose

Shielding

• incident
• radiation
• transmitted
• radiation

Barrier thickness

Consequence

• Using barriers to block or absorb radiation
• Effective shielding depends on the type of radiation
• Common shielding materials include lead, concrete
• Examples: Lead aprons, thyroid shields, concrete walls

Shielding effectiveness increases with thickness/material density

Factors influencing patient exposure in conventional radiography

• Beam energy
• Depending on peak kV and filtration
• Regulations require minimum total filtration to absorb lower energy photons
• Added filtration reduces dose
• Goal should be use of highest kV resulting in acceptable image contrast
• Collimation
• Area exposed should be limited to area of CLINICAL interest to lower dose

Additional benefit is less scatter, netter contrast

Grids

• Reduce the amount of scatter reaching image receptor
• But at the cost of increased patient dose
• Patient size
• Thickness, volume irradiated and dose increases with patient size

Except for breast (compression): no control Technique charts with suggested exposure factor for various examinations and patient thickness helpful to avoid retakes