Session 5 - Radiotherapy

Question 1

What is a major issue with radiation therapy?

Answer 1

Potentially carcinogenic

Question 2

Give two local controls used in current cancer treratment

Answer 2

Surgery

Radiotherapy

Question 3

Give two systemic controls used in current cancer treatment

Answer 3

Chemotherapy

Immunotherapy

Question 4

Give three palliative controls used in current cancer treatment

Answer 4

Radiotherapy
Chemotherapy
Immunotherapy

Question 5

What percentage of cancer patients undergo radiotherapy at some point?

Answer 5

50%

Question 6

Give three types of radiotherapy

Answer 6

External beam
Brachytherapy
Unsealed sources

Question 7

What is the objective of radiotherapy

Answer 7

To maximise dose to tumour

Minimise dose to normal tissue

Question 8

What does the process by which radiation is absorbed in a cell depend on?

Answer 8

Energy of the photons

Chemical composition of the absorbing material

Question 9

What is the comptom process?

Answer 9

High energy photons ionise atoms in a tissue and proceed through it at a reduced energy level. Many fast electrons are produced which will go on and ionise other atoms of the absorber and produce a deflected/scattered photon of reduced energy.

This process is independent of atomic number of absorbing species and thus avoids practicioner having to avoid tissues with differing tissue density.

An example of this process is found in radiotherapy.

Question 10

What is the photoelectric process?

Answer 10

Low energy photons will ionise atoms and produce fast electrons but will in themselves be entirely absorbed. This varies rapidly with the atomic number.

An example of this process is found in diagnostic x-rays.

Question 11

What are the two methods by which ionising radiation acts to kill cells?

Answer 11

Directly

Indirectly

Question 12

What is the directly acting method by which ionising radiation kills cells?

Answer 12

– If the atoms of the target molecule (DNA) are ionised this is a diret effect. This cannot be modified by sensitisers and protectors

Question 13

What is the indirectly acting method by which ionising radiation kills cells?

Answer 13

If the radiation interacts with other molecules (H20) to produce free radicals that migrate to DNA. This accounts for 2/3 of cellular damage and is modified by sensitizers and protectors.

Question 14

What is the principle target of ionising radiation in radiotherapy?

Answer 14

DNA of cancer cells

Question 15

Why is DNA the primary target in radiotherapy?

Answer 15

Only needs to damage a few essential genes to induce apotposis

Question 16

Chemically, what are three things radiation can do to DNA to damage, and give two examples of each

Answer 16

Base damage
•	Thymine Glycols
•	8-Hydroxyguanine
Sugar damage 
•	Abasic sites
•	Strand break lesions
Strand breaks 
•	Single strand breaks
•	Double strand breaks

Question 17

Why are double strand breaks critical cell killing leasions

Answer 17

. Double strand break repair is error-prone in mammalian systems. Misrepaired Double Strand Breaks are the principle lesions of radiation mutation and visible chromosomal aberration formation.

Question 18

What is therapeutic gain?

Answer 18

The dose at which you can attain tumour control AND acceptable damage to normal tissue

Question 19

How is therapeutic gain achieved? (2 ways)

Answer 19

Fractionation

Multi-Beam Conformal Radiotherapy

Question 20

What is fractionation?

Answer 20

Fractionation of the radiation dose (splitting of the total dose into many single doses) produces, in most cases, better tumour control for a given level of normal tissue toxicity than does administration of a single large dose.

Fractionation spares normal tissue by allowing for damage repair between doses.

Question 21

What is the issue with tumour hypoxia in cancer, and how does fractionation overcome this?

Answer 21

Proteins produced in hypoxia, such as Hif-1 and CA IX, can cause radioresistance. Fractionation allows radiotherapy to overcome this resistance by spreading out the doses over time in order to allow the previously hypoxic cells to become oxic and vulnerable to radiation.

Question 22

What is multiple beam radiotherapy?

Answer 22

Allows the radiologist to superimpose the x-ray dose over the tumour bearing region – allowing a high dose to hit the tumour volume with sparing of adjacent tissues.

This combined with a multi-leaf collimator allows the radiologist to shape the x-ray beam to the tumour shape, in order to allow a high dose region to fit the tumour volume, with greater sparing of adjacent tissue.

Question 23

What is protonic therapy?

Answer 23

A form of radiotherapy which presents energy “peak” once it reaches target tissue, before dropping off rapidly.

Allows targeted irradiation of tumour and minimal damage to surrounding tissue.

Question 24

What is an issue with protonic therapy?

Answer 24

Tumours rarely fall neatly into braggpeak, and therefore multiple proton beams must be used in order to facilitate effective treatment

Question 25

What are the advantages of protonic therapy?

Answer 25

, the lack of soft tissue damage surrounding the tumour is still significant enough to warrant its use on the treatment of tumours in vulnerable locations, such as the brain.

Question 26

What is a universal carcinogen?

Answer 26

Radiation

Induces cancer in most tissue of most species of all ages, as a result of all penetrating nature.

Question 27

How many cancer deaths result directly from radiotherapy?

Answer 27

3680/year

Question 28

Outline nuclear medicine imaging

Answer 28

• Radiopharmaceuticals are taken internally, by intravenous injection or via injection.
• External detectors (gamma cameras) capture and form images from the radiation emitted by the radiopharmaceuticals
• Differ from other tests in that they show the physiological function of the system being investigated. Generally more organ or tissue specific than those in conventional radiology imaging, which focus on a particular section of the body.
• Can be used for whole body bone scans in evaluation of bone related pathology

Question 29

Give three uses of nuclear medicine imaging

Answer 29

analyze kidney function.
visualize heart blood flow and function.
scan lungs for respiratory and blood flow problems.
identify inflammation in the gallbladder.
evaluate bones for fractures, infection, arthritis and tumours.
determine the presence or spread of cancer in various parts of the body.
identify bleeding into the bowel.
locate the presence of infection.
measure thyroid function to detect an overactive or underactive thyroid.
investigate abnormalities in the brain, such as seizures, memory loss
and abnormalities in blood flow.
localize the lymph nodes before surgery in patients with breast cancer or
melanoma.

Question 30

What is a PET scan?

Answer 30

A nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide which is introduced intot hebody on a biologically active molecule. 3-d images of tracer conc within body are then constructed by computer analysis. In modern scanner 3-d imaging is often accomplished with the aid of a CT X-ray scan performed on the patient during the same session, in the same machine.

If the biologically active molecule chosen for PET is FDG, an analogue of glucose, the conc of tracer imaged give tissue metabolic activity n terms of regional glucose uptake. Use of this tracer results in the most common types of PET scan.