Radiation Protection and Patient Safety

Question 1

What does ICRP stand for?

Answer 1

International Commission on radiological protection

Question 2

What types of population radiation is there?
What’s the average amount a person in Australia gets?

Answer 2

Natural background radiation (terrestrial, cosmic, radon and progeny, internal/ingestion) = 1.5 mSv per year = 75 XRs
Artificial sources (medical exposure, consumer products/activities, atmospheric weapons testing). 1.7 mSv for diagnostic imaging
3 mSv on average

Question 3

What are the categories of exposure?

Answer 3

Occupational (excludes medical and background radiation)
Medical (includes support persons and volunteers in medical research)
Public (excludes occupational, medical and natural background

Dose limits only apply to occupational and public exposures

Question 4

What are the aims of radiation risk protection principals?

Answer 4

to manage and control exposures to ionising radiation so that tissue effects are prevented and the risk of stochastic effects are reduced to the extent reasonably achievable

Question 5

What are the types of exposure situations?

Answer 5

• Planned: protection planned before exposure and magnitude can be predicted
  
  • Includes medical exposure of patients
• Emergency: unexpected situations that may require urgent protective actions
  
  • Eg nuclear disasters
• Existing: known existing exposures that warrants radiological protective actions
  
  • Eg radon in swellings, naturally occurring radioactive material (NORM)

Question 6

What are the principals of radiation protection?

Answer 6

Justification - Any radiation exposure situation should do more good than harm
Optimisation - Radiation exposure should be kept as low as reasonably achievable (ALARA) taking into account economic and societal factors
Limitation - The total dose to any individual other than for medical exposure of patients should not exceed the appropriate regulatory limits

Question 7

What is the lifetime theoretical risk limit for induction of cancer and hereditary effects?

Answer 7

5% including risk of induced cancer and hereditary defects

Question 8

What is the dose limit for staff in radiology?

Answer 8

20 mSv per year (on average over 5 years) with a max of 50 mSv in any one year

Question 9

What is the tissue effect limit for lens, skin and hands/feet?

Answer 9

Lens 20 mSv (newly decreased)
Skin 500 mSv (dose is averaged over 1cm2 of any part of skin regardless of total area exposed)
Hands/feet 500

Question 10

What is the dose limit for a fetus?

Answer 10

Same as the public, 1 mSv

Question 11

What is the dose limit recommendation for carers and volunteers?

Answer 11

ICRP recommends 5 mSv for adults supporters. AMC suggests 1 mSv per diagnostic test, 5 mSv per therapeutic application
Volunteers 5 mSv per year. Discourage children/pregnant women. Consent must be sought

Question 12

What are some practical ways to decrease dose?

Answer 12

Time:
- work quickly but effectively
- use features such as LIH, virtual collimation, acquisition replay
Distance:
- inverse square rule: doubling the distance will x4 reduction
- NM patients act as line sources, inverse rule
Shielding:
- lead everything, aprons at least 0.25mm Pb
- perspex (plastic) for positron/beta transmission in NM

Question 13

What is a TLD?

Answer 13

Thermoluminescent dosimeter
- Exposed XRs excite the electrons in the valance band > conduction band
- Energy is released as light when heated
- Light emitted from photomultiplier is directly proportional to radiation exposure - completely reusable
- Materials include primarily lithium and calcium
- Need to correct for tissue equivalence

Question 14

What is OSL?

Answer 14

Optically stimulated luminescent
- Ceramic beryllium oxide
- Near tissue equivalent for photon
- Requires laser light to stimulate readout
- High uncertainty rate

Question 15

Whats the difference between radiation incident and radiation emergency?

Answer 15

Radiation incident:
Any unintended event, the consequences or potential consequences of which are not negligible from the POV of protection and safety
Radiation Emergency: Situation of exposure as a result of an accident, malicious act, or any other unexpected event and requires prompt action in order to avoid or reduced adverse consequences

Question 16

The responsible person must do what post radiation incident/emergency?

Answer 16

Report cause, consequence, steps taken to remedy the situation and prevention steps

Question 17

What are some typical XR doses?

Answer 17

Extremites, skull, c-spine: 0.1 mSv
Rest of spine, abdo, pelvis, mammo (2 views): 0.1-1 mSv

Question 18

What are some typical CT doses?

Answer 18

2-3-4-5 (roughly)
head-neck-chest-abdo

SPECT/CT and PET/CT are >10mSv

Question 19

What are some typical fluro/angio doses?

Answer 19

Barium swallow/meal (mouth) 1-5 mSv
barium enema, angio (coronary, pulmonary, PCI) 5-10 mSv
angio abdo, aortography, TIPS, RF cardiac ablation >10

Question 20

What are some typical NM doses?

Answer 20

Myocardial perfusion, lung scan, gated cardiac pool 2-3 mSv
Bone scane 5mSv
PET/CT >10

Question 21

What’s the equation to calculate entrance skin dose (ESD)?
(in Xray)

Answer 21

ESD = entrance skin air kerma (ESAK) (mGy) x (backsplatter factor) BPF
BSF usually ~1.3
Therefore skin dose ~30% higher than ESAK

Question 22

How do we calculate dose area product (DAP)/kerma area product (KAP) in fluoro?

Answer 22

dose in air (mGy) x area of beam (cm2) = mGy.cm2

DAP stays consistent regardless of distance from tube

Question 23

How do we measure dose in CT?

Answer 23

weighted CT dose index (CTDI_w) creates an average of CTDI between centre and periphery of phantom/person in a single slice (mGy)
CTDI_vol (more commonly used now in helical scanner) takes into account non-contigous scanning. CTDIvol = CTDIw/Pitch (mGy)
Dose length product (DLP) factors in the legnth of the scan to show overall output. DLP (mGy.cm) = CTDI x scan length
- DLP can be converted to effective dose using DLP conversion coefficients

Question 24

How do we measure dose in NM?

Answer 24

Administed activity = mega-becquerel
Individual dosimetry difficult to establish
Monte Carlo techniques

Multiply the cumulated activity (total activity in source organ) by S factor (dose absorbed by target organ per unit of cumulated activity in the course organ) to get absorbed dose to target organ

Question 25

How do we measure fetal doses in different modalities?

Answer 25

XR: approximated using entrance skin dose (ESD)
- using percentage depth dose (PDD) table, fetus usually ~8cm below skin which is 25% of dose
eg abdo XR 2.5mGy, 25% of that is 0.6 mGy

CT: scanning of areas not including the baby is negligible dose (up to max 1mSv in 3rd trimeter chest imaging)
- 10-20 mSv for primary abdo scanning (single phase)

NM: higher doses received since you’re injecting radio contrast
10-20 mSv, can be higher

Question 26

CTPA vs VQ for pregnant women

Answer 26

Fetal dose <0.1 mGy/negligible CTPA, 0.5mGy VQ
breast dose 5-10mGy CTPA, <1mGy VQ
Maternal effective dose 5 mSv vs 2mSv

Question 27

What are facility reference levels (FRLs)?

Answer 27

Dose exposure levels that can be used to compare to the diagnostic reference levels (DRLs)
- 75% cutoff using submitted FRLs

Question 28

What are some dose optimisation techniques?

Answer 28

Collimation - blades that limit the dose area and reduce scatter
Filtration (Al, Cu) - filters out low energy beams although lose contrast
Max kilovoltage - higher energy = better penetration = lower input for same output but you need to change other settings
Distance - further the better (inverse square rule). Reduce angulation
Compression - mammo
Grids - remove in children and large air gaps
Automatic exposure control (AEC)/automA/automatic brightness control (ABC) - ensures steady dose/same image quality despite pt weight and will self cease

NO:
Gonadal shields - no clear evidence and may need to repeat scan
Magnification - dose increases (by square of magnification if moving pt closer). just collimate better

Question 29

Principals in high risk pt groups

Answer 29

Pregnant women: can proceed if negligble dose. If >1mSv, needs discussion
Women of childbearing capacity: ask about pregnancy status. avoid pelvic imaging
Children: avoid use of grids. mechanical immobilisation, possible chemical. gain rapport
Breast feeding: avoid NM (variable effects from nothing, pump and dump to very toxic)

Question 30

What is the LD 50/60 in humans?

Answer 30

4 Gy