Part 12: Beam Modifiers: Bolus

Beam Modifiers purpose

to make isodose curves more uniform below the skin surface

Beam modifiers

List:

1. Wedges

2. Bolus

3. Tissue Compensators

Term. Bolus

def. any tissue equivalent material

What does the bolus do?

Acts as a beam modifier evening the shape of the isodose curves under the skin

Superflab bolus

Though not practical, what would be the best bolus material?

Water

Bolus Materials

1. Superflab (brand)

2. Superstuff (brand)

3. Rice Pellets

4. Sugar Pellets

5. Spiders Mix

6. Paraffin Wax

7. Wet Gauze

8. Vaseline Gauze

9. Water Filled Balloons

10. Polystyrene (not common)

What material are superflab and superstuff made out of?

Petroleum products

What is in Spiders mix?

Besides bolus material, paraffin wax can be used for

neutron protection

Polystyrene is more commonly used for

dosimetric buildup

(fyi: for dosi to test Dmax)

True or False: The primary purpose of the bolus is to be used as a beam modifying device

False

What is the primary purpose of bolus material?

Increase surface dose

For:

• nodes

• scars

• skin cancer

Why don’t we just use KV instead of using electron beam?

Even though KV has a skin surface dose,

A small amount of dose passes though the patient with KV x-rays

With electron: essentially 0 dose after a few cm

What is the disadvantage of a bolus as a beam modifier?

Loss of skin sparing due to electron build-up

(FYI: cuz we are moving Dmax closer to the surface. There is electron contamination)

(FYI2: with wedges this does not happen)

Bolus is only used as a beam modifier for __

1. electron therapy (e.g. wax bolus on nose)

2. KV x-ray therapy

3. Fill in gaps for tissue deficits

Why is bolus only used for the following therapies?

1. electron therapy (e.g. wax bolus on nose)

2. KV x-ray therapy

Dmax is already at the skin surface so we don’t need to worry about losing skin sparing

Give two examples of how bolus can be used to fill in the gaps for tissue deficits.

1. removed eye

2. sinus

How is bolus used in air gaps?

Give an example.

The dose to the other side of an air cavity is ↑ than it would be if the tissue was homogenous.

Prevent tissue rxns to the other side of an air cavity using a bolus

Example: Wet/Vaseline gauze in nostril

How would we apply bolus to even the isodose curves in a skin cancer treatment on nose?

1. make nose look square with wax

2. Insert Vaseline gauze in nose

Bolus:

1. If the bolus is flat, it is being used __

2. If the bolus is irregularly shaped, it is being used __

1. to increase surface dose

2. as a beam modifier