55. RADIOTHERAPY Flashcards
1
Q
- What is Radiation Therapy?
A
- this is using ionising radiation to kill tumours
- lethal doses of radiation are rapidly delivered
to malignant tumour cells
2
Q
- 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
3
Q
- 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
4
Q
- What do we weight up in cancer therapy?
A
- the small future risk
IS WEIGHED AGAINST
- an existing life-threatening disease
5
Q
- What kind of cells are malignant tumour cells?
A
- they rapidly reproduce
- they are easily affected by radiation
6
Q
- What is a difficult task when it comes to Radiotherapy?
A
- destroying enough of the tumour
- to prevent its regrowth
7
Q
- 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
8
Q
- 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
9
Q
- 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
10
Q
- 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
11
Q
- 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
12
Q
- 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
13
Q
- 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
14
Q
- What happens when we increase the dose?
A
- we increase the number of cells killed
- we increase the amount of the tumour killed
15
Q
- What are the significant features of these curves?
A
- THERE IS A THRESHOLD DOSE
- for cell killing
- THE FRACTION OF CELLS KILLED INCREASES
- with the dose
- this follows a characteristic S-Shaped curve - THERE IS A DOSE AT WHICH 100% OF THE CELLS
- are killed
- there will be no further effect if the dose is increased
16
Q
- 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
- What 4 factors does the dose-response curve depend on?
A
- The tissue from which the cells originate
- The type of ionising radiation used
- Its energy
- The rate at which the radiation dose is given
18
Q
- What happens when we deliver the dose more rapidly?
A
- more damage is caused
- with a lower threshold
19
Q
- What do healthy cells tend to have?
A
- they have a better DNA repair mechanism
20
Q
- 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
- 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
- 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
- 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
- For which regions of the body is radiation especially effective?
A
- regions of the body that are suffering with superficial
skin cancers
25
Q
- What does the responsiveness of the tumour differ from?
A
- the responsiveness of the neighbouring healthy tissues
26
Q
- Which 2 factors does the cure rate and the effectiveness of the Radiation depend on?
A
- Cancer Type
- Specifics of individual cases
27
Q
- When do we make use of Radiation therapy?
A
- we use it as a Palliative measure
- this is if a cure is unlikely
