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Biology of Cancer SSC > Radiotherapy in Cancer Management > Flashcards

Radiotherapy in Cancer Management Flashcards

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1
Q

Why is radiation a two edged sword?

A

Can treat and cause cancer

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2
Q

What can radiotherapy be used with?

A
  • Surgery
  • Chemotherapy
  • Immunotherapy
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3
Q

When would it be used with surgery?

A

Local control of disease

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4
Q

When would it be used with chemotherapy/immunotherapy?

A

Palliation for improved QoL eg in alleviating painful bone metastasis

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5
Q

What are the 3 types of RT?

A
  • External beam radiotherapy
  • Brachytherapy (sealed source)
  • Unsealed source
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6
Q

What is the aim of radiotherapy?

A

To maximise does to the tumour and minimise dose to the normal tissue

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7
Q

Is RT potent?

A

Yes

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8
Q

Is RT cost effective?

A

Yes

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9
Q

What % of cancer patients require RT at some point?

A

50%

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10
Q

How many of those treated with RT are treated with curative intent?

A

60%

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11
Q

What is the survival rate for those treated with RT?

A

> 70%

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12
Q

What do electromagnetic radiations interact with?

A

Electrons

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13
Q

What can absorption of radiation lead to?

A
  • Excitation (raising e- to higher level)

- Ionisation (ejection of e-)

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14
Q

What does x-ray absorption depend on?

A
  • The energy of the photon

- Chemical composition of the absorbing tissue

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15
Q

What process occurs with high energy photons?

A

The compton process - fast electrons produced and a deflected/scatterd photon with a lower energy.

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16
Q

What level of photon energy does diagnostic radiology use?

A

Lower energy

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17
Q

What is the process that occurs with lower energy photons?

A

Photoelectric process - fast electrons produced but the photon is entirely absorbed.

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18
Q

Why is the compton process used for radiation therapy?

A

It does not depend on atomic number of the absoring species so the problem of differential absorption by different tissues is avoided. Don’t want bone to be able to shield a tumour.

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19
Q

How can ionising radiation act at a molecular level?

A
  • Directly

- Indirectly

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20
Q

What happens in directly acting ionisation?

A

The atoms of the target molecule aka DNA are ionised

21
Q

What happens in indirectly acting ionisation?

A

The radiation interacts with other molecules to produce free radicals that migrate to the DNA

22
Q

Can direct acting ionisation be modified?

A

Generally not

23
Q

Can indirect acting ionisation be modified?

A

Yes, by sensitisers and protectors

24
Q

What is an important quality of ionising radiation?

A

The energy is not uniformly released and is deposited unevenly.

25
Q

What is the biological effect of ionising radiation determined by?

A

Photon energy size ie how concentrated is the beam? Very. This is why its so lethal.

26
Q

What is the principle target for the effects of ionising radiation?

A

DNA

27
Q

What kind of damage is ionising radiation very likely to cause?

A

Double stranded breaks

28
Q

What other damage can ionising radiation cause?

A
  • Base damage
  • Sugar damage
  • Single strand breaks
29
Q

What are unrepaired DSBs thought to be?

A

Critical cell-killing lesions

30
Q

How is the dose of radiation administered?

A

It is fractionated

31
Q

What is the benefit of fractionation?

A

It spares normal tissue by allowing time for damage repair beteen doses (normal tissue recovers better than tumour tissue)

32
Q

Why does normal tissue recover better than tumour tissue?

A

Normal tissue has a full compliment of DNA so full compliment fo DNA repair mechanisms. Tumour tissue has compromised DNA repair.

33
Q

What is expressed by tumours when they become hypoxic?

A

Hypoxia inducable factor 1 (HIF-1) in region of hypoxia

34
Q

What is the problem by hypoxic tumour cells?

A

They are radioresistant but still viable

35
Q

How can we exploit this?

A

Dose fractionation - radiation kills some oxic cells. This allows reoxygenation of some of the hypoxic cells, which can then be targetted in the next dose of radiation.

36
Q

What does multi-beam radiotherapy allow?

A

We can superimpose the dose over the tumour bearing region so the tumour gets a high does but the adjacent tissues are spared somewhat.

37
Q

What can be used alongside superimposing the beams?

A

Multileaf Collimators

38
Q

What do multileaf collimators do?

A

Shape the beam to the tumour volume

39
Q

What is this combination called?

A

3D-Conformal Radiotherapy (3D-CRT)

40
Q

What is the standard treatment in the UK?

A

3D-CRT

41
Q

What is an Arc IMRT?

A

New method of radiation using a 360 degree beam

42
Q

What is the downside of Arc IMRT?

A

No tissue is spared completely - all tissues get at least a small dose of radiation.

43
Q

What is the Bragg peak?

A

Pronounced peak on the Bragg curve which plots energy loss of ionising radiation as it travels through matter

44
Q

Where does the Bragg peak occur for protons?

A

Immediately before the proton comes to rest

45
Q

What is the clinical relevance of the Bragg peak for protons?

A

It is lower than the exposure given from photons/x-ray beam so overall lower level of exposure to surrounding tissues.

46
Q

What is the SOBP?

A

The spread out bragg peak - the sum of the indiviual Bragg peaks at staggered depths.

47
Q

So why are protons better?

A

They can be targetted to stop at a certain point, where as x-rays go through the point and out the other side, causing more damage

48
Q

Why is radiation a weak carcinogen and mutagen?

A

Its such a good cell killing agent - dead cells don’t cause cancer.

Biology of Cancer SSC (16 decks)

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