Rad Safety

Question 1

List the categories of exposures according to the International Commission on Radiological Protection.

Answer 1

Situations:
1. Planned
2. Existing
3. Emergency

Individuals:
Occupations
Public
Medical

Question 2

Eye dose

Answer 2

20mSv in a year over 5 years, with no single year exceeding 50mSv.
Or 0.5Gy threshold

Question 3

Pregnant staff

Answer 3

Carry out a risk assessment - nil need to cease working

Dose limit 1mSv to foetus

Question 4

Types of dosimeters

Answer 4

Film Badge
TLD
OSL
EPD

Question 5

Film badge

Answer 5

Cheap, permanent record

Question 6

TLD

Answer 6

Thermoluminescent dosimeter - reusable and more sensitive than film

Question 7

OSL

Answer 7

Optically stimulated luminescence - stimulated by light, read by a laser, no dose-fading

Question 8

EPD

Answer 8

Electronic personal dosimeter - silicone diode detector that allows instant reading, but expensive and fragile

Question 9

3 key points of radiation protection

Answer 9

1. Time (reduce exposure time)
2. Distance (from rad source)
3. Shielding

Question 10

Name 3 techniques for X ray protection

Answer 10

1. X ray tube position - scatter towards floor
2. Positioning - out of way of rays
3. Shielding

Question 11

3 techniques for Nuclear Medicine protection

Answer 11

1. Time: reduce close contact with pt (post injection of radioisotope)
2. Distance: maximise distance from pt
3. Shielding: structural shielding (lead aprons not effective in NM)

Question 12

What is ‘radiation incident’

Answer 12

unplanned or unexpected irradiation of at least 5mSv for staff or 1mSv for public.
Must be reported and investigated, inform relevant stakeholders.
Usually still indicates under control.

Question 13

What is ‘radiation accident’

Answer 13

Any of:
- use of radioactive substance 50% more than prescribed
- use of wrong radioactive substance
- unintended irradiation due to equipment malfunction
- Radioactive substance given to wrong pt or wrong part of body

Question 14

Emergency exposure

Answer 14

Uncontrolled irradiation, usually indicating a larger scale (20-100mSv, more people)

Question 16

Diagnostic Reference Levels

Answer 16

Ensures irradiation from usual procedures are within an expected and acceptable limit.

Question 17

Name 3 methods to monitor radiation dose in patients.

Answer 17

1. Direct measurement
   a) surface dosimetry (TLD or OSLD) or ionisation chamber at the end of tube (Dose-Area Product meter)
   b) Cumulative Air Kerma - for peak skin dose estimation, considers backscatter factor
   c) CT Dose Index + Dose Length Product
2. Calculating effective doses

Question 18

Typical X ray doses

Answer 18

Chest + thoracic spine <0.1mSv
Rest ~0.3mSv
MMG 0.44mSv

Question 19

Typical CT doses

Answer 19

head + chest lower (0.06, 0.02)
CTAP ~0.7mSv

Question 21

List 4 safety concerns in MRI

Answer 21

1. Static magnetic field interacting with metallic implants - MRI safety sheet
2. Gradient coils creating noise - ear protection
3. RF field - heating in conductive leads could cause burns
4. Gd contrast - nephrogenic system fibrosis in renal impairment)

Question 22

MRI and pregnancy

Answer 22

No evidence of safety concerns to foetus
Small amount of GD can reach breast milk, but not absolutely contraindicated

Question 23

US safety

Answer 23

Non ionising however still deposits energy in tissues - heat/thermal index (potential cell damage), bubbles in biological fluid can resonate and increase in size > collapse to cause shock wave > microvascular damage
Mechanical Index used to indicate potential risk of Cavitation

Question 24

What is KERMA

Answer 24

Kinetic Energy Released per unit MAss
Air KERMA usually in the context of QC for measuring tube output

Question 25

Absorbed dose

Answer 25

Amount of energy deposited per unit matter (Gray = Joule/kg)

Question 26

Equivalent dose

Answer 26

Measure to assess the biological effect of irradiation, takes the type of rad into consideration.
H = DxWr in Sv

Question 27

Effective dose

Answer 27

Considers irradiation to different body parts according to their tissue types/susceptibility. Unit: Sv

Question 28

Flaw of MGD

Answer 28

Assumes 4.2cm breast tissue thickness, 50% adipose and 50% glandular tissue
Real life usually 6cm thick and <20% glandular

Question 29

MMG safety

Answer 29

Must not exceed 3mGy (legal)
Should not exceed 2mGy (best practice)

Question 30

Diff between absorbed dose, equivalent dose, effective dose

Answer 30

Absorbed dose - energy deposited in a standard mass of tissue (Gy)
Equivalent dose - tissue sensitivity to irradiation (Sv)
Effective dose - dose that represents overall risk from irradiation (Sv)

Question 31

Deterministic effect

Answer 31

Known threshold = non-random in occurrence
Higher dose = higher severity
2000mGy = erythema

Question 32

Stochastic effect

Answer 32

Random
No known threshold
Probability of effect occurring increases with increasing dose

Question 33

Risk estimation

Answer 33

Linear No Threshold (LNT) - higher dose = higher probability of stochastic effects

Linear Quadratic Response (LQR) - low dose = more likely to repair damage, higher risk at higher doses (sigmoid shaped relationship)

LNT said to overestimates potential harm

Question 34

Skin dose at which erythema and epilation occur

Answer 34

2-5Gy
Pts who exceed 2Gy should be followed up

Question 35

Skin dose at which moist desquamation occurs

Answer 35

> 15Gy