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MED 107- MEDICAL PHYSICS II > 55. RADIOTHERAPY > Flashcards

55. RADIOTHERAPY Flashcards

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1
Q
  1. What is Radiation Therapy?
A
  • this is using ionising radiation to kill tumours
  • lethal doses of radiation are rapidly delivered
    to malignant tumour cells
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2
Q
  1. What regime are these doses of radiation in?
A
  • they are in the Deterministic Regime
  • this means that a predictable fraction of the tumour
    cells dies
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3
Q
  1. What is the disadvantage of exposing tumour cells to high doses of radiation?
A
  • we expose healthy tissues to these high doses
  • the treatments deliver a stochastic dose of radiation to
    the rest of the body
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4
Q
  1. What do we weight up in cancer therapy?
A
  • the small future risk

IS WEIGHED AGAINST

  • an existing life-threatening disease
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5
Q
  1. What kind of cells are malignant tumour cells?
A
  • they rapidly reproduce
  • they are easily affected by radiation
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6
Q
  1. What is a difficult task when it comes to Radiotherapy?
A
  • destroying enough of the tumour
  • to prevent its regrowth
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7
Q
  1. What is the end goal of Radiation therapy?
A
  • the total extinction of tumour cells

THIS IS BECAUSE:
- if one cell is left behind
- the tumour will reseed

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8
Q
  1. When is cancer exceptionally dangerous?
A
  • when it is not confined in separate and compact
    masses

THIS MEANS IT CAN:
- spread throughout the body
- it can infiltrate vital

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9
Q
  1. What region of the body do we treat when we treat cancer?
A
  • we treat the entire region that is infected
  • this is often surrounded by healthy tissue
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10
Q
  1. What compromise must we make when deciding on the radiation dose chosen to eradicate the cancer?
A

A COMPROMISE IS MADE BETWEEN:
- the effectiveness in tumour killing
- the ability to spare nearby healthy tissue

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11
Q
  1. What is the issue with the treatment dose used in this graph?
A
  • we have undesirable consequences present

THE FIRST DOSE IS TOO LOW:
- few healthy cells are killed
- some tumour cells survive
- the tumour can reseed

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12
Q
  1. What is the issue with the treatment dose used in this graph?
A
  • we have undesirable consequences present

THE THIRD DOSE IS TOO HIGH:
- too many healthy cells are killed
- no tumour cells survive
- the tumour cannot reseed

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13
Q
  1. What is ideal about the treatment dose used in this graph?
A
  • there is an overlap between the two curves
  • a large enough number of tumour cells is killed
  • while ensuring that a very small number of healthy
    cells are killed
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14
Q
  1. What happens when we increase the dose?
A
  • we increase the number of cells killed
  • we increase the amount of the tumour killed
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15
Q
  1. What are the significant features of these curves?
A
  1. THERE IS A THRESHOLD DOSE
    • for cell killing
  2. THE FRACTION OF CELLS KILLED INCREASES
    - with the dose
    - this follows a characteristic S-Shaped curve
  3. THERE IS A DOSE AT WHICH 100% OF THE CELLS
    - are killed
    - there will be no further effect if the dose is increased
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16
Q
  1. What happens if the threshold for the healthy tissue exceeds that for the tumour?
A

WE USE A DOSE THAT:
- kills most of the tumour cells
- affects relatively few of the healthy cells

17
Q
  1. What 4 factors does the dose-response curve depend on?
A
  1. The tissue from which the cells originate
  2. The type of ionising radiation used
  3. Its energy
  4. The rate at which the radiation dose is given
18
Q
  1. What happens when we deliver the dose more rapidly?
A
  • more damage is caused
  • with a lower threshold
19
Q
  1. What do healthy cells tend to have?
A
  • they have a better DNA repair mechanism
20
Q
  1. How do we use the healthy cells tendency to have better DNA repair mechanisms to our advantage when using Radiotherapy?
A
  • we divide the high dose that is required to kill the
    tumour cells
  • into many fractions
  • this is known as Fractionation
21
Q
  1. What are the advantages of Fractionation?
A
  • it protects the healthy tissue
  • it gives the healthy tissue time to repair, recover and
    repopulate
22
Q
  1. How does Fractionation work?
A
  • smaller doses are delivered with a pause of a day or so
  • this pause exists between the fractions
23
Q
  1. How does using fractions damage the tumour cells?
A
  • it changes the point in the cell cycle
  • at which the tumour cells are irradiated
24
Q
  1. For which regions of the body is radiation especially effective?
A
  • regions of the body that are suffering with superficial
    skin cancers
25
Q
  1. What does the responsiveness of the tumour differ from?
A
  • the responsiveness of the neighbouring healthy tissues
26
Q
  1. Which 2 factors does the cure rate and the effectiveness of the Radiation depend on?
A
  1. Cancer Type
  2. Specifics of individual cases
27
Q
  1. When do we make use of Radiation therapy?
A
  • we use it as a Palliative measure
  • this is if a cure is unlikely

MED 107- MEDICAL PHYSICS II (108 decks)

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