Topic 21: Radiation protection practical aspects

Question 1

when are Dose area product and Dose Length product used?

Answer 1

dap used in diagnostic radiology except ct DLP used in ct

Question 2

How do you calculate the DAP?

Answer 2

X-ray beam area x absorbed dose (because area increases by ^2 and absorbed dose decreases by ^2 so its always the same)

Question 3

How do you measure the dose in CT?

Answer 3

We put a long thin ionisation chamber in the iso-centre. measure dose along z-axis. The DLP.

Question 4

How do you obtain the CT dose index?

Answer 4

CTDI = dose profile in mGy.cm (from the ionisation chamber)/nominal beam width

Question 5

How do you measure the weighted CTDI?

Answer 5

1/2 CTDI_centre + 2/3 CTDI_periphery

_{in air or perspex phantom}

Question 6

In a IRR Risk assesment, what do you need to consider? This was a past paper exam question! EEEK RISKKKKKKK

Answer 6

1. WHAT KINDA RADIATION MAN? Nature of radiation source
2. HOW FUCKING MUCH IS IT MATEDose rates
3. YOU PROTECTING YOURSELF MATE? Do you have personal protective equipment on?

Question 7

What do we have to protect the radiologists from in interventional radiology?

Answer 7

secondary scatter

Question 8

Interventional radiology risks?

Answer 8

What are the potential doses?

• Base on workload, type of case, distance from patient

Question 9

Precautions

Answer 9

• PPE - personal protective equipment like lead aprons and thyroid shields
• Mobile shielding (lead screens)
• Dose reduction
• Personal monitoring
• Training

Question 10

what does “ALARP” mean?

Answer 10

as low as reasonably practicable

Question 11

When designing a radiation facility room it should be designed with the aim to keep radiation levels ALARP and to ensure dose limits are not exceeded. What do you have to consider?

Answer 11

• Dose constraints
• Occupancies outside the facility
• Choice of shielding material
• Provision for dismantling and decommissioning
• Ease of cleaning and decontamination

Question 12

What will the selection of shielding materials depend on?

Answer 12

Obviously : the radiation type and energy and how well it can block

The mass of the material - too heavy might be impractical.

Uniform materials are better

Is it PRICEYYYYY??YAO

Question 13

Shielding calculations include calculations of required barrier thickness, taking workloads and occupancies into account, to ensure appropriate dose constraints are not exceeded.

What do you need to know for a shielding calculation?

Answer 13

• Primary beam and scattered beam dose-rates
• Beam directions
• Workload
• Distances to barriers
• Dose constraint outside of room

Question 14

What is the dose constraint for if we have “dose limits” already?

Answer 14

It is the upper level of dose to an individual useds at the design or planning stage

dose constraint < dose limit

Question 15

What is the barrier factor?

Answer 15

_{B = <u>design dose constraint (t)</u>}

^{air kerma incident on barrier (t) x occupancy}

Question 16

When assessing facilities what do you need to check?

Answer 16

• Whether specified level of protection exists
• Check whether there are any gaps in shielding

Question 17

When does site monitoring occur?

Answer 17

at installations or after modifications

periodic checks

following incidents