Chapter 15 - Beam Restriction PowerPoint

Beam restriction is another word for

collimation

What does beam restriction do?

Decreasing the field size, decreases the ESE by absorbing scatter radiation (decreases patient dose)

ESE

Entrance Skin Exposure

Most common type of collimator?

Variable Rectangular Collimator (manual)

What is PBL?

Positive Beam Limiter (automatic collimator)

#1 priority of beam restrictors?

less dose to patient

#2 priority of beam restrictors?

less scatter produced

The shutter on the collimator

is a device usually made of lead fixed to an x-ray tube housing to intercept the useful beam

What is the collimator used for?

to block any stray radiation which includes leakage & secondary radiation

Allowed leakage amount

1 mGy per hour at a distance of 1 meter from tube housing

Not collimating may result in

• Increased scatter production

• Increased patient dose