Lec #2 - Minimizing Exposure to pt.

Question 1

What does ALARA mean?

Answer 1

As Low as Reasonably Achievable

• Radiation exposure should be kept “as low as reasonably achievable”

Question 2

How do you deal with involuntary motion when taking an exposure?

Answer 2

decrease time inc mA

– or example: exposing pt on respirator when full inspiration

Question 3

What is the minimal (SSD) source-to-skin distance?

Answer 3

Atleast 30cm or 12 inches.

Question 4

When would doing a procedure PA vs AP be beneficial?

Answer 4

• Attenuation of low energy photons
• Reduction of photons hitting gonads, breast tissue, thyroid

Question 5

What is PBL? (positive beam limitation)

Answer 5

PBL – automatic collimation – ensures light doesn’t go larger than IR.

Question 6

What does HVL mean?

Answer 6

Half-value layer (HVL)
- The thickness of a designated absorber (e.g., aluminum) required to decrease the intensity of the primary beam by 50% of its initial value

Question 7

What is the minimum lead eq. for gonadal shielding?

Answer 7

Tested on a yearly basis and must have a lead eq. of 0.25 mm

Question 8

What is the maximum amount of leakage from the tube allowed?

Answer 8

leakage radiation 1 m from the x-ray source under
- 1 mGya/hr
- (100 mR/hr)

(when tube is at max settings, voltage and current)

Question 9

What is distance requirement from skin for fluoroscopic equipment

Answer 9

Requirement:

• no less than 38 cm (15 inches) for stationary fluoroscopes
• no less than 30 cm (12 inches) for mobile fluoroscopes
• (typically lower mA for fluoro)

Question 10

What does dead-man switch refer to?

Answer 10

• Foot pedals for fluoro that need to be pressed down in order to expose.

Question 11

How do u calculate ESE (entrance skin exposure)

Answer 11

ESE = mR (or mGy) x (SCD/SOD)2
SCD = source to chamber distance (dosimeter)