Radiation Oncology (Oncological Management)

Question 1

Mechanism of radiotherapy

Answer 1

Xrays consist of photons impacting against cells, causes free electrons being flung off:
1. Direct mechanism: e- breaks DNA (hits DNA)
2. Chemical reaction: e- reacts with H20 to create free radicals
= induces mitotic cell death

Question 2

What are the units of radiotherapy?

Answer 2

1. Gray (Gy):
   Represents dose (amoutn of energy deposited per kg)
2. Fraction: xxx

Question 3

Types of radiation

Answer 3

Neo adjucvant: use preoperative to enhance clearance by surgeon
Definitive: get rid of cancer directly
Adjuvant: give radiotherapy after, to improve

Question 4

Definitive

Answer 4

Lung cancer
Prostate
Cervical
Oesophageal

Question 5

Neo-adjuvant

Answer 5

Rectal cancer (treat the pelvic LNs prior to surgery)
Soft tissue sarcoma of thihg (Eradicate microscopic disease prior to surgery)
Oesophageal cancer (downsize the tumour prior to surgery)

Question 6

Adjuvant

Answer 6

Breast (pospo radio to breat to treat micrscopic diseaa)
HEad and neck cancer (to treat nicrsocpic)
Lypmha (Post chemo radioterhpy to treat sites of buik disease)

Question 7

Radical

Answer 7

xx

Question 8

What is the difference between radical and palliative dose?

Answer 8

xxx

Question 9

What are the common indications of palliative radiotherapy?

Answer 9

• Pain relief
• Control of fungation or ulceration
• Reduction of mass effect
• Haemostasis

e.g. palliation of painful bony rib mets

Question 10

Dose per fraction

Answer 10

How much radiation we are giving to the patient:

Normally it is 2Gy per day

Question 11

What are the 4 R’s of radiobiology

Answer 11

Repair
Redistribution
Reoxygenation
Repopulatino

Question 12

Explain ‘Repair’ of the 4 R’s

Answer 12

DNA injury can be repaired after a dose of radiation. Normal cells repair radiation damage, unlike tumours. The maximal time of repair is 4 hours. Therefore giving treatment once daily or daily fractions, allows damaged normal tissue to repair.

Cancer cell mechanisms have poor repair mechanisms

Question 13

Redistribution

Answer 13

Certain phases of the cell cycle are radiosensitive. Cells can be in the sensitive or resistant phase. Redistribution refers to the cells redistributing to a more sensitive phase over time.

Enhances cell kill with fractionated dose.

Question 14

Reoxygenation

Answer 14

Cells on the periphery are well oxygenated, cells on the inside lack oxygen (necrotic in the middle).

Knock out cells more oxygenated (periphery), then as they are knocked out the inner cells have a circumference of oxygenation now ->continued cycle of killing, and smaller population of cells

More reoxygenation that occurs, the more effective the radiotherapy.

Hyperbaric O2 to improve radiation therapy.

Question 15

Repopulation

Answer 15

Phenomenon of cancer cells in response to treatment.

Accelerate population. Surviving cells grow faster than before.
Therefore Rx should be completed as soon after it is have begun. Avoid treatment break by managing side effects.

Question 16

Acute radiation side effects characteristics

Answer 16

Acute:

Occurs during and soon after radiation (

Question 17

Chronic radiation side effects characteristics

Answer 17

Occurs after > 6mths
Irreversible
Fibrosis and vascular occlusion (ischaemia)

Question 18

Acute radiation side effects?

Answer 18

Acute:
Skin: red, dry, peeling, hair loss
Mucous: Mucositis
GIT: Diarrhoesa, naeusea, vomiting

Question 19

Chronic radiation side effects?

Answer 19

Skin: Atorphy fibrosis, alopecia
Boewl: Fibrosis bowel
CNS: Necrosis of CNS
Viscera: Organ failure: renal failure, spinal cord myelopathy
Second malignancy

Question 20

Steps of radiotherapy

Answer 20

1. Simulation or Setup: CT scan to takes piccys
2. Plan: contouring (mark things you do and don’t want to treat)
   Radiotherapy planning: where to radiation beams and dose
3. Treatment delivery

Question 21

What is image guided radiotherapy?

Answer 21

Cancer can move e.g.
Prostate cancer: can put three seeds of gold in prostate before Rx (surrogate for prostate position), take a picture

Lung cancer: can move with breathing

Can predict movement or follow

Question 22

Breast cancer and IHD - what is the deep breath hold?

Answer 22

Deep breath hold - technique to change position of organs. heart moves away from chest wall -> less radiation to heart (especially LAD artery, therefore reducing IHD)