Radiation Therapy (RT) Basics




Radiotherapy planning can be quite simple or very complex depending on:

  • The aim of treatment (palliative v curative)
  • Tumor location
  • How much radiation is required to kill that particular type of cancer

When high dose radiotherapy is given, it is really important that the patient is absolutely still during treatment and that the treatment "set up" is reproducible from day to day.

Immobilization Devices

Planning usually starts with a visit to the mould room.

Here a mask or other immobilization device is made for the patient to wear during treatment.  The mask is made with a plastic that becomes soft with heat and then sets when it cools.  Thus an impression of a part of the body can be made.

This mask is used for:

1. Patient immobilization - for precise, reproducible treatment, patients should not be able to move.

2. So that reference marks (to show where the radiation should go) need not be on the patient's skin, but can be placed on the mask instead.

Below is a picture of a patient in a treatment mask:


Below are some examples of different immobilization devices: 

Immobilization Device


Preparation of Device

Special characteristics

Bite block

Stabilize jaw to ensure same mouth position each time

Dental impressions are taken
Fixed to a calibrated arm, which is attached to the treatment couch

Only used if child will bite down firmly on the piece

Thermal plastics

Used for head placement

Plastic sheets make masks to fit contours of patient head and face

Causes slight increase in radiation surface dosage

Vacuum-molded thermoplastics

Can be used to stabilize a variety of different body parts

Vacuum draws plastic tightly over cast, plastic mold may be fitted to the body part and fastened to the treatment couch

Good visibility (clear)
Can draw directly on it

Polyurethane foams

Used for a variety of body parts

Place body part on a polystyrene bag that is filled with chemicals, chemicals generate expanding polyurethane foam

Requires skill to be done properly
Fumes are produced

Vacuum bags

Conforming bag that can be reused for several patients

Patient lies on bag in treatment position
Air is evacuated from the bag
Bag conforms to body

Can be adjusted after forming and reused for several patients
Require increased surface dosage




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