Radiation Safety Training for Radiology Personnel

2009

Radiation Safety Division

919-515-2894

Every Job has a Risk or Hazard

Some Greater Than Others

Some Hazards are Not Life Threatening

Some are Potentially Dangerous

Even the Best Jobs Have Hazards

X-Ray Production and Handling Radioactive

Materials are Our Job

What are the Hazards?

How do we Protect Ourselves.

 Dose received by an individual in the course of employment in which the individual’s assigned duties involve exposure to radiation or radioactive material.  Does not include background radiation or medical administrations.

Occupational Dose

• Dose received by a member of the public from exposure to radiation or radioactive material under control of the licensee.  

• Does not include background radiation or medical administrations.

• This relates to those in our building, working in the office but not radiation workers.

Public Dose

Permissible Dose Limits   Occupational Limits for Adults

– Whole Body 5,000 mrem / yr – Eye 15,000 mrem / yr – Extremities or Skin 50,000 mrem / yr – Pregnancy (Declared) 500 mrem / 9 mo.

   General Public 100 mrem / yr

Uncontrolled Dose Rate 2 mrem in any 1 hourThese occupational limits are set by the NRC. Our ALARA limits

are examined quarterly and the quarterly limits are 2.5% of the annual occupational limits set by NRC.

Roentgen – exposure in air RAD- absorbed dose

Dose Equivalent is the amount of damage a type of radiation does to a tissue. This is equal to the absorbed dose times a weighting factor (WR) (WR for x-rays, gamma

rays, and beta particles =1)

Standard Units = Rem

The Rem is the unit in which dose is recorded and reported on an individuals dose history

SI Units = Sievert (Sv) 1 Sv = 100 Rem

This is the unit that is used for your dosimetry reports!!!

Units of Radiation Exposure

Diagnostic Testing:Radiography, Nuclear Medicine, CT

Radiation Oncology- Linac- Brachytherapy- Thyroid Ablation

Research:Radiopharmaceuticals

Radiation Sources at CVM

X-Ray Production

Cathode – negatively charged electrode in tube; source of electrons; consists of a filament and a focusing cup

Anode – positively charged target

Rotor – rotates anode in order to dissipate heat in the tube

Source of X-Ray Exposure:Animal Holding

Necessary, BUT!

- Use with Care!

- Share the

Assignment

Guidelines for Staff Always wear lead

aprons, thyroid shields if in room during exposure

Dosimetry on outside of apron

Listen for warning devices (door alarm, area monitors)

Maximize distance from exposure

Select best position in room

Radioactive MaterialsNuclear Medicine and Research

•Radionuclides: Tc99m & I-131 (also, P-32, I-125, Cs-137, Ir-192 – generally in laboratories or sealed sources.)

•Diagnostic Radio-pharmaceuticals used in Nuclear Medicine studies may be oral, IV, or inhaled

Radionuclide Activity and Half Lives

Quantity of radiation is expressed in Curies – 1 Ci =3.7 x 1010 disintegrations per second

•Bequerel (Bq) SI unit used to express activity - 1 Bq = 1 dps

1 Bq = 3.7 x 10-10 Ci

The physical half-life is defined as the amount of time it takes for a radioactive isotope to decay to ½ of its original

activity.

Example: 50 Ci after one t ½ = 25 Ci

Example: Tc-99m t 1/2 = 6.02 h

P-32 t 1/2 = 14.3 d

I-131 t 1/2 = 8.02 d

Body also has a biological half life that shortens activity time in body! Release of patients depends on both!

When Working With Nuclear Medicine Patients When Working With Nuclear Medicine Patients & Radioactive Materials and Byproducts . . . .& Radioactive Materials and Byproducts . . . .

Wear Personnel Protective Apparel

Wear Badges

ALWAYS WEAR GLOVES!!

Dispose of Sharps in Sharps Containers

Check hands, shoes, body for contamination

Procedures for Nuclear Medicine Patients

Proper Protective Apparel for Workers– Lab coat– Gloves

Cages posted with “Caution Radioactive Materials” sign

NO handling of animals unless medically necessary

Cages may not be cleaned until released by Nuclear Medicine

First Priority: personnel decontamination

removal of contaminated apparel/articles

mild cleansing of the skin

Skin acts as a protective barrier.

Damage compromises this important natural protection

Do not scrub hard!!,

Do not use very hot water!!!

Second Priority: Restrict Area of Contamination

and Prevent Spread

Decontaminate Objects

DECONTAMINATIONDECONTAMINATION

Radiation Oncology

Linac – External Radiation Beam Treatment

Patient set up and then treated with no worker in the room. Patient must be anesthetized and immobilized each day for treatment.

Brachytherapy – Internal Radiation Treatment

Catheter implanted in patient in surgery and loaded with ribbon containing radioactive “seeds”. Worker dose potential high with set up and placement of ribbon. Workers have minimal patient interaction until ribbon is removed –potentially one week.

Thyroid ablation – “Cat Clinic” – Internal Radiation Treatment

I 131 administered to cat and cat kept in cage during treatment. Worker dose potential high with administration and handling of waste. Controlled access to room. Minimal patient interaction during treatment.

Reasons for Accidental Exposures

1) Not following written operating procedures (restraints vs holding; fluoro time;

time/distance/shielding; unnecessary repeats) 2) Human Error

(Lead aprons only cover one side; quick exposure finger)

3) Insufficient X-ray Safety Training(No knowing the equipment,

regulations/procedures)

ALARAAs Low As Reasonably Achievable Time Distance Shielding Dosimetry Monitoring Preventive Education

All personnel radiation exposure shall be maintained to the lowest reasonable level. Overexposures are documented, investigated and

mitigated. Exceeding annual exposure limit can lead to

administrative limitation of radiation related duties per the Radiation Safety Officer/Radiation Safety Manual.

Inverse Square Law

Distance 1 ft 2 ft 3 ft 4 ft 5 ft 6 ft 10 ft

Exposure rate 100 25 11 6.25 4 2.8 1 mR/hr

Exposure rate 1d2

…………….

Exposure rate is proportional to the inverse square of the distance away from a point source :

Radiation Monitoring

Whole Body Badge

Extremity/Ring Badge

TLD DosimetryThermoluminescent Dosimeter

RADIATION ENERGY is stored in a LiF crystal and later released as light energy by annealing the TLD

Minimum sensitivity is ~30 millirem for X-rays

LiF crystal is behind the label

OSL DosimetryOptically Stimulated Luminescence

Dosimeters

RADIATION ENERGY is stored in a Al2O3 crystalline detector. The radiation exposure signal contained in the Al2O3 material is depleted upon stimulation with the green light.

Minimum sensitivity is ~ 5 kev for photons

The radiation exposure signal contained in the Al2O3 material is depleted upon stimulation with the green light.

Multi element filter pack sandwiches the Al2O3 crystalline detector and places it behind the identifying information on a ring or badge.

Dosimeter Recommendations

Wear It! Wear It Properly!Store Away From Radiation Sources !

Don’t Wear Someone Else’s!Keep It Cool and Dry!Exchange it at the First of Each Quarter!

Immediately Notify Us if it is Lost!

10,000 PEOPLE10,000 PEOPLE

AGES 20 - 65AGES 20 - 65

No Occupational Exposure

1 REM additional exposure

2,500 2,500 Cancer Cancer VictimsVictims

2,503 2,503 Cancer Cancer VictimsVictims

Professional Risk

Declared Pregnant Workers

Workers must declare pregnancies in writing with the Radiation Safety Office (specific form)

Additional monitoring is assigned and bioassays if needed (fetal badge for waist)

Exposure limit for pregnancy is 0.5 rem to fetus/embryo (monitored monthly)

Confidential recordkeeping; written request accepted for release of records.

Radiation Sources to the Pubic and Personnel in Radiology

Primary Beam or Scatter passing through barriers such as walls and exposing individuals on the other side. Anyone not badged is considered general public!

Shielding Design and post installation survey ensure they are within acceptable limits. Take into account workload and occupancy on other side of barrier.

Doors to X-ray Rooms not being closed during exposure/Unnecessary personnel in room during exposure.

Under technologist control to ensure safety by closing doors and asking personnel to leave.

Radiation Exposure to Patients and Personnel

Area of Body Exposed – Important to always restrict or collimate to field of interest and Shield.

Higher Area = Higher Scatter Exposure

Technique – Set for optimum visualization.

Overexposure particular problem with CR/DR.

Higher Technique kvp/Mas = Higher Exposure

Number of Exposures – Conserve by: - Positioning – Proper angles to demonstrate

A.O.I. Proper alignment of part of receptor essential with CR/DR.

Reduce Motion – Restraints and supports to maintain stability.

CR and DR

Basic principles same as screen/film, with some changes in terminology.

Receptor exposure -> Signal strength

Subject Contrast -> Signal difference

But visual cues and reinforcement are lost due to rescaling.

Routine overexposure is common.

Screen Film Vs. DR/CR

Screen/film:

Δ signal strength (Exposure) = Δ Optical density

Δ signal difference (kVp) = Δ Contrast

Δ Processing =Tendency to degrade contrast.

Digital systems:

Δ signal strength = No change in brightness.

Δ signal difference = Δ Contrast

Δ Processing = More effect on contrast than kVp.

Results

Over exposure : Photon intensity at the receptor is

more than required to produce an optimal image.

Patient/Staff dose increased.

Possible loss of contrast

Repeat unlikely

Under exposure: Photon intensity at the receptor is

LESS than required to produce an optimal image.

Increase in mottle

Small detail structures lost

Repeat likely.

Overexposure Vs. Optimum Exposure

Automatic Rescaling can create similar density on films regardless of mAs. Allows for wider latitude of acceptable technique

However, if too little exposure is used, the image detail is lost.

Therefore, to decrease repeat rates, many use excessive exposure and manipulate with rescaling to attain proper density. Allows for reduced repeats, but what is the cost?

Increasing Dose Problem

Under exposed images = noisy images

In general, radiologists complain about noisy images

at > 40% below appropriate exposure level.

Over exposed up to 3X may be okay for the image but is it - OK ?

Radiographers tend to use more exposure to avoid criticism for noisy images.

A popular saying “When in doubt , burn it out.”

Justification: “It’s OK since the we repeat less images.”

2004 ALARA in Digital RadiographyConference Recommendations.

Increasing Exposure and Potential Staff Dose to Reduce Repeat Rates Does Not Equal Out!

Conference Recommendations.

•Improve staff education – As with S/F systems, using Optimum Techniques is best.

• Monitor exposure indicators.

• Repeat all images overexposed > 3X.

- Allowing more Violates ALARA, and

- Establishes poor practice standards.

These recommendations are just the beginning, Stay Tuned, There Will Be More to Come

Questions/Concerns

Any time we can help, please call us:

Radiation Safety Division at

515-2894

8:00 am to 5:00 pm M - F

Emergency After Hours Contact -

NCSU Public Safety at 515-3333