MOD 7 - Measuring and Minimizing Radiation Exposure

the most current method of measuring radiation exposure

absorbed dose (D)

absorbed dose (D)

Amount of energy the patient receives from exposure to ionizing radiation

how is D measured

• unit

using ionization chambers, the energy of exposures is measured and quantified as J/kg and expressed by the unit Gray (Gy)

air kerma

• unit

• application

Energy released from a beam of radiation per unit mass in air

• expressed in J/kg or Gy

• applies to individuals exposed

effective dose

• unit

• application

Quantifies the type of radiation and the radiosensitivity of the tissues

• expressed in Sv or mSv

• stochastic response within an exposed population

EfD are correlated to

correlated to population risk but the results can be calculated from a single imaging exam

EfD calculation

• absorbed dose x tissue weighting factor x quality factor

• D x Wt x Wr

Quality Factor

essentially the Wt that compares the potential for biologic damage between various sources of ionizing radiaton

lowest and highest QF sources

lowest:

• X-Rays, Gamma Rays, Beta Particles

• 1 QF

highest:

• fast neutrons

• 20 QF

equivalent dose

• a product of absorbed dose and quality factor to allow exposures to be compared between the various sources of radiation

• expressed in Gy

Dose Area Product (DAP)

modern method of measuring and recording patient exposure that is built into current radiography and fluoroscopic equipment

DAP calculation

DAP (mGy-cm²) = air kerma (Gy) x exposure field size (cm2)

DAP proves

how reducing field size with collimation reduces PT dose

DAP is highly dependent on

individual characteristics, such as

• dimensions

• BMI

• weight distribution

• gender

Cumulative air kerma (CAK)

expression of dose accumulated from an entire fluoroscopy procedure (mGy)

Safety Code 35 applies to

large medical radiological facilities

SC35 does NOT apply to

radiation therapy, dental, mammography, or small radiological facilities

Owner Responsibility

• Equipment and install meet safety standards

• Radiation safety program developed, implemented and maintained

Responsible User Responsibilty

Monitor/manage radiation safety program

General Radiation Technologist Responsibility

• monitor personal exposure

• ALARA

• possess recognized qualifications and documented training- CAMRT

Referring Practitioner Responsibility

• Responsible to ensure the prescribed procedure is JUSTIFIED based on professional experience, judgement and common sense

• Give consideration to alternative non-ionizing diagnostic procedures

• Be aware of risks/benefits to inform patient

when is a staff required to wear a personal dosimeter according to SC35

when they’re likely to receive more than 1mSv per year

ion chambers

most common type of radiation measurement tool

types of personal monitoring devices

• Film badges

• Thermoluminescent dosimeters (TLD)

• Optically stimulated luminescence (OSL)

where should PMD be worn

if a protective lead apron is worn, the dosimeter must be worn beneath the apron at waist level

where are PMDs sent for evaluation

Landauer

dose limit for occupational radiation workers

20mSv (whole body equivalent exposure) per year

MRTs that regularly working in interventional, fluoroscopy rooms and OR imaging should…

appropriate lead protective clothing and a second OSL that is worn at the collar level on the outside of the lead protection to measure data related to the unprotected regions

TLDs

single use and expensive personal dosimeter device but accurate over a small energy range of 20-250keV

TLD dosimetry process

1. after 3months of use, the TLD is sent to the provider for process

2. uses heat to release the stored energy in the form of light

3. PMT measures the amount of light emitted

4. light signal is recorded and converted to the estimated radiation dose

cause of incorrect dosimetry data

• putting it in washer, dryer

• exposed to scatter

OSL

most common radiation monitoring device used in British Columbia

OSL Dosimetry Process

1. after 1year of use, the OSL is sent to the provider for evaluation

2. laser causes stored energy to be released as emitted light

3. light intensity signal is analyzed by a photoiodide

4. information is related to a radiation dose

Procedures for Reducing Patient Dose

1. justification

2. optimization

3. repeat reduction

4. distance/shielding