Radiation Therapy

Question 1

What are the three indications for radiation therapy?

Answer 1

Incompletely resected tumours, Non-resectable tumours and pain control.

Question 2

How does radiation therapy affect cells?

Answer 2

Direct and indirect damage to DNA (direct to DNA, and indirect by producing free radicals which then damage DNA).

Question 3

What are the three possible pathways a cell can take when hit with radiation? Which is desirable?

Answer 3

1) Proliferation of cells (undesirable)
2) Cell death (most desirable)
3) Alive but unable to divide (beneficial in RT)

Question 4

In what unit is radiation measured? How does the amount of grey’s delivered affect the cell response?

Answer 4

Grey’s. 10Gy-100Gy to cause intermitotic death.

Question 5

What are the 4R’s of radiation?

Answer 5

Repair, repopulation, re-oxygenation and redistribution.

Question 6

What is fractionation?

Answer 6

The total dose of radiation used to treat a tumour is usually divided into a number of fractions.

Question 7

Why is fractionation important? How do the 4R’s fit in?

Answer 7

Fractionation spares normal tissues because it allows REPAIR of sublethal damage and REPOPULATION. It increases damage to tumour cells because of REOXYGENATION and REDISTRIBUTION.

Question 8

How does fractionation help the repair of normal tissues?

Answer 8

It is assumed that tumour cells are less able to repair DNA. Therefore by adding another dose, it spares repaired normal cells, and kills non-repaired tumour cells.

Question 9

How does fractionation help the repopulation of normal tissues?

Answer 9

RT can stimulate cell division by cells by “accelerated repopulation”. In normal tissues, this is kept under control by homeostatic mechanisms.

Question 10

How does fractionation help to increase the damage to tumour cells by reoxygenation?

Answer 10

Tumour has poorly oxygenated necrotic centre which is not radiosensitive. Oxygenated cells are radiosensitive, between doses it allows necrotic centre to become oxygenated.

Question 11

How does fractionation help to increase the damage to tumour cells by redistribution?

Answer 11

Cells are more radiosensitive to RT in M/G1/G2. Time between doses gives time for cell to move from S to more sensitive stages.

Question 12

What types of radiation can be used in radiotherapy? Which machines can use them?

Answer 12

Orthovoltage: Photons (X-rays), not really used.
Cobalt-60: Photons (Gamma rays)
Megavoltage “Linear accelerator”: Photons (X-rays) or Electrons.

Question 13

What are the characteristics of using photons in radiotherapy?

Answer 13

Highly penetrative, slow dose reduction, penetrates normal tissue. Needs CT based treatment planning. Fixed energy.

Question 14

What are the characteristics of using electrons in radiotherapy?

Answer 14

Various energies, not very penetration, good for superficial use. e.g. injection site sarcoma. Rapid dose reduction.

Question 15

What is the protocol in curative radiation therapy? What kind of side affects does curative RT produce?

Answer 15

More low doses, usually has ACUTE side effects rather than late side effects.

Question 16

What are the absolute indications for curative radiation therapy? What kinds of tumours would it be used as the primary treatment?

Answer 16

When RT shows better results than other therapies. Primary Tx in Nasal tumours, brain tumours (palliative doesn’t work), oral tumours (SCC), epulis.

Question 17

In what types of tumours is curative radiation used as post surgery adjuvant RT?

Answer 17

Soft tissue sarcomas, feline injection site sarcoma (usually needed to cure)

Question 18

What is the protocol in palliative radiation therapy? What kind of side affects does palliative RT produce?

Answer 18

Few big fractions used, more likely to cause late effects, but usually don’t expect them to live that long.

Question 19

What two types of radiation therapy protocols?

Answer 19

Curative and palliative.

Question 20

What types of tumours might you use palliative radiation therapy on?

Answer 20

Radiosensitive tumours that are highly metastatic e.g. histiocytic sarcoma, oral melanoma, haemangiosarcoma, MCT grade III