Radiotherapy in Cancer Management Flashcards Preview

SSC- Biology of Cancer > Radiotherapy in Cancer Management > Flashcards

Flashcards in Radiotherapy in Cancer Management Deck (92)
1

What is radiation therapy? 

An often used and successful modality in the 'local' treatment of cancers 

2

What is the problem with radiation therapy? 

There is a risk of inducing a variety of human cancers

3

What cancer treatments are used to achieve local control of the disease? 

  • Surgery
  • Radiotherapy 

 

4

What cancer treatments are uesd to treat disseminated disease? 

  • Chemotherapy
  • Immunotherapy

 

5

What cancer treatments are used for pallitation? 

  • Radiotherapy
  • Chemotherapy
  • Immunotherapy

 

6

Is radiotherapy delivered as a monotherapy? 

Rarely 

7

How is radiotherapy used in conjuction with surgery? 

It can be used before or after surgery

8

Why might radiotherapy be used before surgery? 

To shrink tumour so that it is more operable 

9

What are the types of radiotherapy? 

  • External beam radiotherapy
  • Brachytherapy
  • Unsealed sources

 

10

What happens in external beam radiotherapy? 

X-rays are generated externally, and precisely targetted into the body 

11

What happens in bracytherapy? 

A sealed radiation source is inserted into the body

12

What kind of emitters are used in brachytherapy? 

Short range, only a few cm 

 

13

What kind of radiation is used in unsealed source radiotherapy? 

High energy, short range

14

Give two examples of medications used in unsealed source radiotherapy

  • Radioiodine in thyroid cancer
  • Meta-iodobenzylG in neuroblastoma

 

 

15

What allows unsealed source radiotherapy to work? 

Some drugs/chemicals have an affinity for certain organs

 

16

What are the rules for all forms of radiotherapy? 

  • Maximise dose to tumour
  • Minimise dose to normal tissue

17

What % of cancer patients require RT at some stage of their illness? 

50%

18

What % of those treated with radiotherapy are treated with curative intent? 

60%

19

What % of those treated with curative intent have an >5 year survival? 

70%

20

How can radiotherapy improve in the future? 

  • Improvements in tumour control
  • Reductions in toxicity
  • Early detection
  • Increases in tumour sensitivity

 

21

What can x-rays and gamma-rays be thought of as? 

Waves (λv = cc) or as photons (E = hcv)

22

What does the equation λv = cc tell you about x-rays? 

As the frequency goes up, the wavelength must go down to keep Cc constant 

23

What are photons? 

Packets of energy

24

What do electromagnetic radiations (x-rays or gamma-rays) interact with? 

The electronic component of matter

25

What can absorption of energy from radiation lead to? 

  • Excitation - loss of an electron to a higher level
  • Ionisation - actual ejection of the electron

 

26

What happens when an electron is ejected in ionisation? 

The molecule has an unpaired electron, and so is a free radical

27

What is a free radical? 

A chemically reactive entity that causes chemical changes to exposed atoms and molecules 

28

What damage can be caused by free radicals? 

Lethal damage or mutation 

29

What kind of damage is good in terms of radiotherapy? 

Lethal damage, as want to kill the tumour cells 

30

Why it mutation bad in radiotherapy? 

Because there is a change in function, which can be detrimental in a normal cell 

31

What does the process, at an atomic level, by which x-rays are absorbed depend on? 

The energy of photons, and the chemical composition of the absorbing material

32

What process of absorbtion dominates for high energy photons? 

The Compton Process

33

What happens in the Compton process? 

A photon interacts with loosely bound 'free' electrons, of low binding energy. Part of the photon energy is given to electron, knocking the electron out. The photon then proceeds with a reduced energy (longer wavelength)

34

What is the end result of the Compton process? 

The production of fast electrons, many of which will go on and ionise other atoms of the absorbed. There is also a deflected/scattered photon of reduced energy 

35

What process of absorption dominates for photons of low energy? 

The photoelectric process

36

What happens in the photoelectric process? 

The photon interacts with a tightly bound electron of higher binding energy, and gives up its energy entirely. The electron is ejected, and the photon is entirely absorbed 

37

What is the end result of the photoelectric process? 

The production of fast electrons but no photon

38

/Where are photons of lower energy used? 

In diagnostic radiology 

39

How do the Compton process and photoelectric process differ, in terms of the relevance of atomic number? 

The Compton process is independent of the atomic number of the absorbing species, however the photoelectric process varies rapidly with atomic number 

40

Where are the differences between the Compton process and the photoelectric process important? 

In the application of x-rays to diagnosis and therapy 

41

Which process is used for radiation therapy/ 

Compton process

42

Why is the Compton process important for radiation therapy? 

To avoid the problem of differential absorption in tissues, so bone doesn't shield the tumour 

43

What process is used for diagnostic radiology? 

The photoelectric process

44

Why is the photoelectric process good for diagnostic radiology? 

Because bone differentially absorbs x-rays, resulting in the visualisation of bone structure

 

45

In what ways can ionising radiation at a molecular level? 

Can be directly acting or indirectly acting 

46

What is meant by directing acting ionising radiation? 

If the atoms of the target molecule are ionised

47

Can directly acting ionising radiation be protected against? 

Generally, can only be shielded, can't be modified by sensitisers and protectors

48

What is meant by indirectly acting ionising radiation? 

If the radiation interacts with other molecules to produce free radicals that migrate into the DNA, this is an indirect effect 

49

What % of the body is water? 

70%

50

What happens when ionising radiation hits a water molecule? 

Produces an electron, which becomes solvated by water, and a H2O*+ radical 

51

What happens to the H2O*+ radical? 

It breaks down to produce *OH- and H+

52

What is the problem with the hydroxyl radical (*OH-)? 

It is very reactive, and generates more free radicals from water molecules 

53

What proportion of cellular damage is caused by indirectly acting radication? 

2/3 

54

How can indirectly acting radiation be modified? 

Sensitisers and protectors 

55

What is an important characteristic of ionising radiation, regarding its release? 

The energy is not uniformly released, but deposited unevenly in discrete nm-localised events of concentrated energy 

56

How much energy is released by ionising radiation? 

About 33eV - enough energy to do considerable amount of damage to biological molecules 

57

What is the biological effect of ionising radiation determined by? 

The photon energy size, not the amount of energy absorbed 

58

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

DNA

59

What lesions can be caused by the interaction of ionising radiation with DNA? 

  • Base damage
  • Sugar damage
  • Strand breaks

 

60

Give two examples of base damage that can occur as a result of the interaction of ionising radiation with DNA? 

  • Thymine glycols
  • 8-hydroxyguanine 

 

61

GIve two examples of sugar damage that can occur due to the interaction of ionising radiation with DNA

  • Abasic sites
  • Strand break lesions

 

62

Why are double strand breaks so important? 

  • Unrepaired DSBs are thought to be critical cell killing lesions
  • DBS repair is problematic and error-prone in mammalian systems 

 

63

Why is DBS repair problematic? 

Because you may loose genetic material, causing a sequence change and therefore protein change

64

What is the significance of misrepaired double strand breaks? 

They are the principle lesions of radiation mutation and visible chromosomal aberration formation 

65

How much radiation is given in radiotherapy? 

Typically, 30 fractions of 2Gy each, given Monday-Friday for 6 weeks 

66

What is fractionation of the radiation dose? 

The splitting of the total dose into many single fractions 

67

What is the advantage of fractionation of the radiation dose? 

  • Produces better tumour control for a given level of normal tissue toxicity than the administration of a large dose
  • Spares normal tissue by allowing for damage repair between doses 

 

68

How does fractionations spare normal tissue? 

Normal tissue has its full complement of DNA repair, whereas tumour tissue has compromised repair. This means that only the normal tissue can repair its DNA in the interval 

69

What happens as solid tumours rapidly grow? 

They start to exceed their supply of oxygen and nutrients, and tend to become hypoxic

70

What % of solid tumour cells are hypoxic? 

10-15%

71

What is the problem with hypoxic tumour cells? 

  • They are radioresistant, but still viable
  • They are more aggressive

 

72

What is the difference in dose needed to kill hypoxic cells known as? 

The OER - oxygen enhancement ratio 

73

What is the OER at low doses? 

About 2.5x

74

What can be done to overcome the problem of tumour hypoxia? 

Dose fractionation 

75

How dose dose fractionation overcome the problem of tumour hypoxia?

It allows for reoxygenation 

76

What does multiple beam radiotherapy allow? 

The radiologist to superimpose the X-ray dose over the tumour bearing region, to allow high doses to the tumour volume with sparing of adjacent tissue

77

What needs to be done regarding the positioning in mulitiple beam radiotherapy? 

  • Have to position the patient accurately and reproducibly 
  • Have to adjust to take into account tumour shrinkage using image guided ultrasound

78

What is used to shape the beam to the tumour volume? 

Multilead Collimators 

79

What does the use of multiple beam techniques combined with multi-lead collimators allow the radiologist to do? 

Shape the x-ray beam to the tumour shape to allow a high dose region to fit the tumour volume, with greater sparing of adjacent tissue

80

How is multiple beam radiotherapy developing? 

Now using an increasing number of beams

81

What is the problem with multiple beam radiotherapy? 

No region is left unexposed 

82

What is it hoped will be achieved with fractionation and multi-beam conformal radiotherapy? 

The situation of positive therapeutic gain occurs, whereby the dose required to control the tumour is achieved, with an accetable level of normal tissue damage 

83

What is a proton? 

A subatomic particle with a positive electric charge of 1 elementary charge, and a mass of slightly less than a neutron 

84

What is the Bragg peak? 

A pronounced peak on the Bragg curve which plots the energy loss of ionising radiation during its travel through matter. For protons this occurs immediately before the particles come to rest - the Bragg peak 

85

What does the depth to which the protons penerate into the patient depend on? 

The energy of the proton beam 

86

What is the result of the precise control of the energy of the proton beam? 

It means the proton beam stops at the target, and so the target gets more of a radiation dose than the overlying tissue, and the underlying tissue receives no radiation dose. 

87

How do x-rays compare to protons in term of penetration? 

X-rays are more penetrating than protons, and so cannot be stopped at the target so higher doses of radiation are delivered to surrounding tissues 

88

What have large scale animal studies and epidemiological studies of human populations shown about radiation? 

It is a universal carcinogen

89

What is meant by a universal carcinogen? 

Induces cancer in most tissues, of most species, of all ages 

90

What does the universal nature of radiation as a carcinogen relate to? 

The all-penetrating character of ionising radiation

91

How does the carcinogenic potential and mutagenic potential of radiation compare to other chemical agents/ 

It is a weak carcinogen and mutagen 

92

Why is radiation only a weak carciongen and mutagen? 

Because it is such a good cell killing agent