Lecture 13

Question 1

What are the benefits of radiotherapy?

Answer 1

It is often one of the main reasons for the long-term survival of cancer patients. This is clear when looking at survival rates post mastectomy for surgery and chemotherapy with and without radiotherapy.

Question 2

A tumour requires a ______ dose of radiation than normal tissue, meaning that this dose will kill the cancerous tissue without damaging too much healthy tissue.

Answer 2

Lower

Question 3

What is the linear-quadratic model for radiobiology?

Answer 3

A model that describes the effects of radiation on cell survival. The parameters for this curve are different depending on the tumour.

Linear: a single dose of radiation is sufficient for certain tumours.

Quadratic: some tumours are best suited to multiple events.

Question 4

What is fractionation?

Answer 4

When a dose of radiation is delivered in several smaller fractions (2-4 Gy) so that the tumour is destroyed while the healthy tissue remains intact. The same overall dose is delivered.

Question 5

Describe external beam radiotherapy

Answer 5

Radiotherapy from an external source (a radiotherapy machine) that fires radiation into the patient. Usually, several beams are directed at the patient from several directions.

Question 6

Describe brachytherapy

Answer 6

A set of sealed radioactive sources or seeds are placed into the patient inside the tumour. These are often contained in an applicator tube and are usually removed after a given period of time.

Question 7

What sources are usually used for external beam radiotherapy?

Answer 7

• Cobalt-60 (1.25 MeV)
• X-rays
• Electrons
• Protons, neutrons, heavy ions (rarely)

Question 8

Cobalt-60 is a source of ________ and is used for the _______ ______.

Answer 8

Gamma
Gamma Knife

Question 9

How are electrons for radiotherapy generated?

Answer 9

In a linac at 1-25 MeV

Question 10

Describe how external beam therapy works

Answer 10

Question 11

How is a treatment plan formed for someone who is undergoing external beam radiotherapy?

Answer 11

1) Images are taken of the tumour site.
2) Models are made of the site.
3) The beam is shaped and modulated to provide a suitable dose.
4) Throughout the process the tumour is monitored.

Question 12

What are the four types of dose rates for brachytherapy?

Answer 12

• High dose rate (HDR)
• Low dose rate (LDR)
• Pulsed dose rate (PDR)
• Fractionated doses

Question 13

Define high dose rate brachytherapy

Answer 13

A radionuclide is inserted into the tumour via a catheter and is eventually removed.

Question 14

Define low dose brachytherapy

Answer 14

A small radionuclide seed is inserted and never removed.

Question 15

How is a treatment plan formed for someone who is undergoing brachytherapy?

Answer 15

Prescription schemes for locations and specific sources are created.

Question 16

What is hadron radiotherapy?

Answer 16

Radiotherapy that involves large accelerators at high energies and large magnetic rigidity. The most common type is proton beam therapy but neutron therapy and heavy ion therapy also exist. This is an expensive treatment.

Question 17

What is Boron capture therapy?

Answer 17

A type of therapy in which a neutron source delivers thermal neutrons to a patient with boron in their tumour. Boron is very susceptible to neutrons so many reactions occur inside the tumour and alpha particles produced by these reactions destroy it.