Week 7 - Radiation Protection and Safety

Question 1

Radiation Protection and Safety

Answer 1

• Practitioner operating within an imaging department must have a sound knowledge of radiation protection and safety
• Aim is to reduce the associated risks to staff, patients and the general public to a minimal acceptable level
• Aim of diagnostic imaging is to produce images of the highest diagnostic quality at the lowest radiation dose

Question 2

Physical Effect

Answer 2

Cell death and/or prevention of cell division
o Cannot repair
o Threshold dose above which harmful effect increases with does
o Deterministic Effect

Question 3

Biological Effect

Answer 3

Survival of a mutated cell
o No threshold – probability of harm (e.g., cancerous tumour) increases with dose
o Stochastic Effect

Question 4

Code of Practice

Answer 4

• Establishes the regulatory requirements for the use of ionising radiation in medicine
• Safety guides give practitioners in the three areas a best practice approach to day-to-day clinical work

Applies to:
o Exposure of patients as part of their medical diagnosis or treatment
o Exposure of individuals as part of health screening programns
o Exposure of individuals participating in research programs
o Exposure of individuals as part of medico0legal procedures
o Occupation exposure of individuals
o Exposure of carers
o Exposure of members of the public arising from medical radiation producing equipment and radioactive sources

Question 5

Classes of Exposure

Answer 5

Occupational
o Occur at work and as a result of operations within a workplace

Medical
o Exposure of patients as part of diagnosis or treatment
o Can be controlled at source – shielding and containment, ventilation or dispersal, PPE

Public
o All other exposures not medical or occupational

Question 6

Dose Limits - Occupational Exposures and General Public

Answer 6

• When a pregnancy is declared by a female employee, the embryo or foetus should be afforded the same level of protection as required for members of the public

Question 7

Effective Dose

Answer 7

Occupational
- 20 mSv per year, averaged over a period of 5 consecutive calendar years

Public
- 1 mSv in a year

Question 8

Radiation Protection Principles: Justification

Answer 8

o Before a medical procedure involving exposure of an individual to ionising radiation is approved or commenced, the procedure must be justified for that individual

Question 9

Radiation Protection Principles: Optimisation

Answer 9

o Radiation doses that arise from medical radiation exposures and those received by the public and occupationally exposed persons must be kept as low as reasonably achievable, economic and social factors being taken into account

Equipment and methods must be selected to ensure that the dose administer to a patient for:
- Diagnostic Purposes
o sufficient to enable the procedure to provide the required information
o and not greater than is necessary to provide that information

• Therapeutic Purposes
  o is consistent with the intended radiotherapeutic purpose of the exposure
  o and will achieve the required dose to the target tissue

Question 10

Radiation Protection Principles: Limitations

Answer 10

o All medical applications of ionising radiation must be managed in such a way that radiation doses to occupationally exposed persons and members of the public do not exceed the dose limits specified

o Stochastic effects – No threshold

o Actively optimise – ALARA

o Dose limits for occupational exposure and the general public don’t apply to medical exposures
o Dose Reference Levels (DRL)

Question 11

Diagnostic (Dose) Reference Levels (DRL’s)

Answer 11

• It is difficult to set a dose limit for diagnostic medical imaging procedures
• Dangerous – Image quality is important
• Individual patient dose is dependent of so many factors that one dose limit would never fit all
• Levels that are expected not to be exceeded for standard procedures when good and normal practice regarding diagnostic and technical performance is applied
• Set at a regional or national level, a reflection that there is a wide variation in medical practice between regions
• Not regulatory limit on the dose that can be administered to a patient, it is simply indicative value
• No universal method used to calculate DRL

Question 12

Facility Reference Level

Answer 12

• Median dose delivered to a standard patient undergoing a specific routine diagnostic exposure at a given facility

Can be used to:

• define local facility doses for common procedures
• compare doses between similar protocols
• assess the dose impact of the introduction of new protocols
• compare doses between facilities
• provide a comparative dose metric for optimisation strategies
• indicate compliance with state and territory regulatory requirements

Question 13

Protection of an Embryo or Fetus

Answer 13

Procedure on a pregnant patient that may be in a radiation dose of more than 1 msv to an embryo or fetus must:
- be justified on an individual basis

• include an assessment of the risks to:
  o the embryo or fetus from the radiation exposure
  o the patient if the procedure is not performed

Question 14

Responsibilities

Answer 14

Responsible Person
o Radiation Safety Officer
 Overall responsibility o fensuring a radiation management plan is in place

o Radiation Medical Practitioner
 Radiologist or Radiation Oncologist

o Operator
 Radiographer or Radiation Therapist

All have their own well defined role in the radiation protection and safety of all

Question 15

Risk - Benefit

Answer 15

• Risk = a situation involving exposure to danger
• Benefit = an advantage or profit gained from something
• The two are rarely mutually exclusive

E.g., Financial investment
o The benefit is an increase in capital in the form of interest while there is some risk of decreasing capital or loss

Question 16

Risk and Benefit in Radiology/Radiotherapy

Answer 16

Workers receive occupational risk associated with the exposure but no benefit.
- Someone else (the patient) gets the benefit (risk to staff needs to be kept small)

For medical exposures, the same individual (patient) received the risks and benefits
- A larger risk is acceptable as there are potential benefits for the individual

Question 17

Benefits and Risks: Medical Exposure

Answer 17

Benefits from Medical Exposure
- Successful diagnosis and treatment

Risks from Medical Exposure
- Radiation induced secondary cancers, salivary function, radiation pneumonitis, incontinence, ED, rectal bleeding, paralysis

• Serious hereditary/genetic effects in descendants

Question 18

Absolute Risk Model

Answer 18

The probability that a person who is disease-free at a specific age will develop the disease at a later time following exposure to a risk factor
 The probability of cancer induction following exposure to radiation

Question 19

Relative Risk Model

Answer 19

Assumes that radiation would increase the natural incidence of cancer and is expressed as a fraction of the naturally occurring risk
 Excess Risk

Question 20

Justification and Optimisation

Answer 20

Any decision that alters the radiation exposure to an individual or population has to have an outcome that does more good than harm
o Justification

The requirement always to minimise the risk associated with exposure while maximising the benefit
o Optimisation problem

A wide range of radiation levels are going to be used in diagnostic and interventional radiology

Question 21

Balancing Risk and Benefit

Answer 21

Criteria that should be considered
o Patients clinical condition – what are the benefits of using radiation

o Availability of equipment
 New and changing radiation equipment technology can limit the procedures and protocols

o Availability of personnel
 Personnel must have appropriate training on the equipment to perform a particular procedure

o Alternative Examinations
 Can another non-ionising imaging modality provide the same or similar information
• E.g., MRI, ultrasound

Question 22

Statistical Data surrounding Risk and Benefit

Answer 22

• Caution really needs to be used when interpreting these statistical data
• Only valid for the larger population
• They do not accurately tell us the risk for an individual
• The individual’s sensitivity to ionising radiation will be different depending on their age, sex and other factors

Question 23

Perception of Risk - Communicating Risk to Patients

Answer 23

• Conveying information about a risk to a patient requires an understanding of how people perceive risk or danger

Question 24

Communication Risk

Answer 24

• Avoid using technical/medical jargon
• Translate technical/medical terms into everyday language
• Write or speak short sentences that convey a single point
• Present information in a clear and organised structure
• Need to understand the values systems of the people you are speaking to as these will influence the perception of risk

Question 25

Objective vs Subjective

Answer 25

Objective assessment of risk is used by the scientific community and is based upon peer-reviewed scientific analysis of risks

Public may be getting risk assessment from less technical information sources 
o	Non-peer reviewed publications 
o	Magazines 
o	Newspapers
o	Television shows 

Needs to be taken into account

Question 26

Perception of Risk

Answer 26

• In medical situations patients and their families can be confused, shocked and under a great deal of stress
• In this situation you need to be sensitive to this and understand this
  o People find it difficult to process information and can don’t really her what you are saying
  o People can become distrustful of anything a person is saying and so don’t really hear what you are saying
  o People often give a greater weight to negative information than positive information
   Negativity bias

Question 27

Comparing Risks

Answer 27

• Don’t compare risks for unrelated situations
• There will also be a risk with not having a procedure
• The time scales for side effects from intervention and no intervention are often quite different ant this is difficult to compare
• Risk of a stochastic effect some long time into the future from an exposure to ionising radiation vs a more immediate risk if a procedure is not performed

Question 28

Benefits vs Risks of not performing a procedure

Answer 28

• The risks to consider of not performing an exam include missing a diagnosis and/or initiating treatment too late to improve the medical outcome
• The potential to reduce a patients overall life expectancy due to a disease must also be considered in conjunction with the latency period for radiation-induced cancer and the age of the patient