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
25. What does the responsiveness of the tumour differ from?
- the responsiveness of the neighbouring healthy tissues
26
26. Which 2 factors does the cure rate and the effectiveness of the Radiation depend on?
1. Cancer Type
2. Specifics of individual cases
27
27. When do we make use of Radiation therapy?
- we use it as a Palliative measure
- this is if a cure is unlikely
