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Flashcards in Principles of radiation therapy Deck (56)
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1

How does ionising radiation cause damage?

Indirect damage (most important)
Direct damage (least important)

2

What is the unit for radiation therapy (RT)?

Grey(s) [Gy]

3

Outline basic effects of radiobiology

Mitosis delayed - 1 Grey
Cells cannot divide - 10-100 Gy)
Radiation damaged cell usually die after 1 or 2 attempts at mitosis

4

Which cells in the body are the most radiation sensitive?

BM
Intestinal crypt cells
Germinal layer of epidermis
Tumours

5

Why is fractionation important?

Allows the 4 Rs of radiation therapy to be obeyed:
Repair
Repopulation
Reoxygenation
Redistribution

6

Define REPAIR in the context of the 4 Rs

Tumour cells are less able to repair DNA daage as they are often oxygen and nutrient deficient

7

Define REOXYGENATION in the context of the 4 Rs

Tymours have a necrotic, poor oxygenated centre. A single dose of RT would tend to kill off the healthy, oxygenated tumour cells but may not affect the hypoxic cells. The death of the vascularised cells will make more room for the surviving hypoxic cells.

8

Define REDISTRIBUTION in the context of the 4 Rs

Cells are more sensitive to RT in some phases: M>G2 > G1> ES > LS

The remaning cells willbe 'synchronised and eventually will move into a more sensitive phase. This is the time to deliver the next RT fraction.

9

What type of radiation is used for RT in animals?

X-rays
Gamma rays
Particles - beta particles (electrons) in radioisotopes

10

Describe a Cobalt-60 therapy unit

Radioactive source
Photons
Fixed energy (1.24 MV)
Low technical requirements

11

Outline a linear accelerator unit

Variable energies
Electrons/photons
No radioactivity
High technical maintenance
High accuracy

12

Describe an electron beam

Various energies possible (5-15 MeV)
Rapid dose reduction (depending on energy)
Therapeutically useful depth (1.5-5.6cm)
Single fields, simple dose calculations

13

Outline a photon beam

High penetration
Slow dose reduction
Field arrangements necessary
Penetration of normal tissue
CT-based treatment planning
Sedation sufficient, no GA required

14

What is the best Tx option for nasal tumours?

Radiation therapy

15

Define gross tumour outline

what may be visible on a CT scan

16

Define microscopic disease outline

the peripheries of the disease that may not be clearly visible on a CT beyond the gross tumour outline

17

What are the 2 broad goals of RT?

Curative/definitive (cure or long term control)
Palliative (palliation, stabilisation, pain reduction/relief)

18

How many greys are generally used for curative/definitive RT?

Generally 40-60 but these are fractionated into small amounts

19

Why perform curative RT?

Absolute indications: RT has better results than other therapies

Relative indications: RT shows same tumour control, but other advantages (functional, cosmetic)

Combination therapy: RT+surgery +/-chemo (e.g. ISS for best MST)

20

For what tumours is RT the primary Tx modality?

Brain
Head and neck (oral, nasal)
MCT
Epulis

21

What is an epulis tumour?

Benign,
Require aggressive surgery (e.g. removal of underlying bone)

22

For which tumours is post surgery adjuvant RT indicated?

MCT
STS
FISS

23

What is en bloc resection (EBR)?

used in certain cancers to remove a primary lesion, the contiguous draining LNs and everything in between, as in a modified radical mastectomy

24

Define negative margin

For tumour removal, no cancer cells are seen at the outer edge of tissue that was removed. AKA clean or clear. Sometimes the pathologist will tell you how wide this margin is but there is no uniform definition.

25

Define positive margin.

Cancer cells extend to the edge of the margin. More treatment is indicated.

26

Indications - RT

Local therapy (local Dx, not systemic)
Incompletely resected umours - then this is the Tx of choice: non-resectable tumours (results depend on tumour type) and pain control (bone cancer or metastases)

27

Describe nasal tumours
Describe MST with different Tx

2/3 are carcinomas
1/3 are sarcomas

MST without Tx = 3 months
Surgery alone = 3-6 months (NEVER DO THIS!)
RT alone = 8-20 months
RT + Sx = 47 months (BEST OPTION!!!)

28

Outline pituitary tuours

85% animals show rapid improvement in clinical signs (with RT?)

CS, localisation and size DON'T have prognostic significance

Very few side effects
MST = 24 months

29

Outline common canine oral tumours and their progression free intervals with RT.

ACANTOMATOUS EPULIDES = 90% tumour control. 86% 3 year PFI 4cm.

ORAL SCC: 45Gy 1 year PFI 75%

ORSAL FSA: 33-67% 1 year PFI

30

Define PFI

Progression Free Interval

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