PHYS C4

ICRP

International Commission on Radiological Protection

Established 1927

ARPANSA

Australian Radiation Protection and Nuclear Safety Regulations

Regulates nuclear material and reactor byproducts

Governs most nuclear medicine operations as they use uranium by products; molybdenum and technetium

Permissible dose limits; Waste disposal

Radiation Safety Officer (RSO)

maintain safety, train staff, monitor, and are point of contact for regulatory agencies

needed if workplace has:

• Prescribed x-ray equipment

• Radioactive substances above exemption levels

• High-powered lasers

• Mining operations that disturb or concentrate NORM (Naturally Occurring Radioactive Material)

Principles of Radiation Protection

• Justification: No practice is adopted unless it produces a positive benefit

• Optimisation: Exposure kept as low as reasonably achievable (ALARA), accounting for social and economic factors

• Limitation: Dose equivalent to individuals should not exceed recommended limits

Dose limits

Occupational dose: received from performing work duties, excluding natural background

radiation or non-occupational medical doses

Pregnant workers in radiation-related workplaces have adjusted occupational dose limit, given duties that reduce their exposure

Public dose: received by a member of the public

Occupational dose limits (18+)

Effective dose: 20mSv per year, averaged over 5 years

Equivalent dose eye: 20mSv per year, averaged over 5 years

Equivalent dose skin: 500mSv per year

Equivalent dose hands and feet: 500mSv per year

Public Dose Limits

Effective dose: 1mSv per year

Equivalent dose eye: 15mSv per year

Equivalent dose skin: 50mSv per year

Pregnant Radiation Worker

equivalent-dose limit of 2 mSv for remainder of the pregnancy applied to abdomen so foetus does not receive a dose more than 1 mSv (public dose)

annual occupational radiation doses are low enough that complete working restriction is unnecessary

but pregnant workers are excluded from any employment activity carring a significant probability of high accidental doses (high-dose brachytherapy and fluoroscopy)

second badge dosimeter for abdomen needed and must be checked every month (instead of every 3)

available lead abdomen shielding

Pregnant Patient

no radiological examination is absolutely contraindicated

no dose limits

procedure risk weighed against risk to patient and foetus if procedure is not used

Strategies to minimise foetal dose

customised shielding (5 HVL usually sufficient)

Simulation of treatment with custom phantom to estimate foetal dose and judge shielding efficacy

treatment/shielding modification as pregnancy progresses

total foetus dose should be documented

personal radiation monitoring device examples

Thermoluminescent Dosimeter (TLD)

Optically Stimulated Luminescence Dosimeter (OSL)

Wearing a Dosimeter

about chest level (between waist and collar)

front of badge facing out and not covered by clothes or shielding

ring dosimeter - dominant hand, under laboratory gloves, front face towards radiation source

stored away from radiation sources when not being worn

do not let others wear your dosimeter

only wear during occupational exposure, not if you are patient

never cut open plastic case or remove labels

excahnge every 3 months

common causes of workplace exposure

Careless work

Equipment failure

Inadequate training

workplace exposure risks

High Intensity Exposures: Skin burns and lesions, possible damage to eye tissue

Long-term Chronic Exposures: Possible chromosomal damage, long term cancer risk

Radiation Incident

abnormal event where a source of ionising radiation is uncontrolled temporarily, and a person is exposed to no more than twice expected effective dose

Radiation Accident

more severe abnormal event due to an ionising radiation source remaining out of control and the dispersion of radioactive material or person exposed to over twice expected effective dose

Radiation Exposure Types

• External radiation from handled radioactive materials and source beams. It does not make person/object radioactive as expose stops immediately when source is removed. (x-ray, CT)

• Internal radiation exposure (contamination) from inhalation, absorption, and ingestion. Exposure continues until material is removed as radioisotopes emit radiation as they decay. (PET, SPECT)

Why is internal contamination harder to manage than external exposure?

Continuous exposure and inability to remove

ALARA - As Low As Reasonably Achievable

Radiation exposure be kept as low as reasonably achievable (ALARA) accounting for social and economic factors

Strategies:

Minimie time, Maximise distance, Shielding

PPE

Engineered controls: spill trays for containment, air filtration

Ventilation: fume hoods, glove boxes

Monitoring: dosimeters, surveys

Hygiene: controlled areas, signage, cleaning

Minimising Internal Exposure/Contamination - Technique

Plan the reception/storage/manipulation/disposal of radioactive material

equipment decontamination

Improve dexterity by practicing procedures

Use tools (forceps or tongs) to handle radioactive samples and contaminated items

Minimising Internal Exposure - Housekeeping

Minimise contamination build-up

Mark and label contaminated areas/items to distinguish from uncontaminated areas

Minimising Internal Exposure - Personal Protecting Clothing and Equipment

Respiratory protection

Protective clothing (disposable gloves)

Shielding PPE (lead apron)

Dosimeters

Minimising External Exposure

minimise time

maximise distance

use appropriate shielding

Minimising Time

dose is directly proportional to exposure duration

exposure = exposure rate x time

e.g - using pulsed fluoroscopy instead if continuous radiation

Maximising Distance

exposure reduction obeys the inverse square law (Doubling distance from source reduces exposure by 4x)

e.g standing back from radiation source, ideally behind barrier, before activating exposure

Shielding

Tenth-value layer (TVL) of shielding material: thickness that reduces radiation intensity to 10% of initial value

cost effective (concrete better than metal)

Radiology – lead most common

Radiation therapy – bricks or reinforced concrete

Shielding Materials for particle types

alpha particles: least penetrating, stopped by a sheet of paper or skin, damage internal

organs if ingested/inhaled

beta particles: more penetrating power, penetrate clothing and several cm of air, stopped

by aluminum/wood

gamma and x rays: highly penetrating, lead or concrete is necessary

Neutrons: Penetrating power dependent on speed, concrete, water, and boron used for shielding

what does effectiveness of shielding material depend on

Atomic number

Density

Thickness

Why is lead used for shielding

High atomic number and density means lots of electrons packed tightly which increases chance of x-ray interaction (photoelectric effect or Compton scattering) to improve stopping power/attenuation

Big, stable nucleus and large electron cloud can absorb electromagnetic radiation

RT Bunkers

bunker wall controls primary, scattered and leakage radiation via shielding

entrance (maze and/or neutron door), a primary (double thickness) and a secondary barrier

Rooms adjoining LINAC bunker are minimal use (storeroom)

Ventilation: cycling air in room at least 6 times per hour, to prevent buildup of radioactive gases from photodisintegration and neutron interactions

Control room: outside of the bunker, CCTV and intercom to monitor patients

Emergency shut-off on linac, couch, bunker walls, bunker entry and in control room

Interlocks, visual signage, flashing lights, audible commands/warnings

Maze

Increases the number of scattering interactions that reduce the energy and intensity of radiation before it reaches entrance

Distance helps reduce dose

Neutron Door

lead and borated polyethylene encased in a steel structure

BPE: high-density plastic combined with 5% boron by weight - H for neutron moderation, B for neutron absorption

Lead: in the door core (as bricks or in layers) to shield secondary gamma rays produced by neutrons and other primary x-rays

Steel: thick carbon steel faceplates, with additional steel reinforcement for strength

Medical Imaging Facilities

95% of occupational exposure comes from fluoroscopy and mobile radiography

Control booth barrier windows embedded with lead

Radiography Examination Room

possible to reach operating console without having to enter “radiation area”

x-ray tube housing prevents leakage radiation to reduce patient dose

at least 2.5 mm of aluminum in filtration

curtains/panels/barriers for operating console or between fluoroscopist and patient

Bucky slot cove

Lead sheets in walls and ceiling/floor

Shielding directly behind a chest board

Radiographic Techniques

Increasing kVp reduces patient dose: more x-rays penetrating patient to reach detector, so less tube current and/or a shorter scan time required to achieve image quality

When upper extremities or breast is examined -and/or patient in seated position- they must be positioned lateral to beam and have lead apron to protect gonads

How to avoid repeat imaging

Effective communication with patient

Proper patient preparation (eg. remove necklaces)

Good radiographic skill and knowledge

Minimise motion unsharpness (shorter exposure time, patient immobilisation)

Use of standard exposure factors to prevent exposure creep

Consider necessity of procedure (benefit vs risk)

Reduce number of views

Avoid exposing pregnant women