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Biology Of Cancer > Radiotherapy > Flashcards

Radiotherapy Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is external beam radiotherapy?

A

Treatment is received from an external source

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2
Q

What is brachytherapy?

A

A sealed radioactive source is placed directly into tumours or body cavities

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3
Q

What is unsealed source radiotherapy?

A

Where a therapeutic radioisotope is injected/ingested into the body and has an affinity for the target organ

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4
Q

Give an example of unsealed source radiotherapy

A

Radioiodine for thyroid cancer

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5
Q

Why is radiotherapy an effective way of treating cancer?

A

Very potent

Relatively low cost

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6
Q

What are the two ways of thinking of X-rays and γ-rays? Give the equations

A

As waves: c (speed) = λ (wavelength) x ν (frequency)

As photons E (energy of photon) = h (Plank’s constant) X ν

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7
Q

Relationship between wavelength, frequency and Plank’s constant?

A

As wavelength decreases, frequency increases

Related by Plank’s constant (h)

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8
Q

What is the frequency and wavelength of gamma and X-rays? What does this mean?

A

High frequency, small wavelength
High photon energy
They are more damaging

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9
Q

What does absorption of energy from radiation lead to (regarding electrons)?

A

Excitation - moved to a higher shell

Ionisation - ejection of an electron producing positively charged free radicals

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10
Q

What determines if X-rays are absorbed or not?

A

Depends on the energy of the photos and the chemical composition of the absorbing material

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11
Q

Does the Compton process involve high or low energy protons?

A

High energy

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12
Q

What happens to the photon in the Compton process when it comes into contact with the absorbing material?

A

The hooting interacts with loosely bound free elections of low binding energy
Part of the photon energy is given to the electron as KE
Photon is deflected, and proceeds with reduced energy, or a longer wavelength

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13
Q

Are the photons in the photoelectric process high or low energy?

A

Low energy

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14
Q

What happens when the photon comes into contact with the absorbing material in the photoelectric process?

A

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

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15
Q

What is the photoelectric and Compton process used for? Why?

A

Photoelectric: diagnostic radiology because photons have lower energy so are absorbed by bone

Compton process: radiotherapy because photons have higher energy and so can pass through bone etc to the target site

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16
Q

What does the Compton process produce after the photons are deflected?

A

Production of fast electrons which can go on to ionise other atoms of the absorber

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17
Q

Which process is independent of the atomic number of the absorbing species?

A

The Compton process is independent of atomic number.

18
Q

What is direct acting radiation?

A

The atoms of the target molecule (DNA) are ionised

Cannot be modified by sensitisers or protectors

19
Q

What is indirect radiation?

A

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

20
Q

What is an example of a molecule that indirect radiation can interact with?

A

Water
To produce a hydroxyl radical, hydrogen ion and an electron
(H2O -> OH + H+ + e-)

21
Q

What can the effect of the hydroxyl radical which ionises DNA be modified by?

A

Sensitisers and protectors

22
Q

What kind of damage can ionising radiation cause to DNA?

A

Base damage
Sugar damage - eg abasic sites and strand break lesions
Strand breaks - single or double

23
Q

Why is good to induce double strand breaks?

A

Of unprepared, thought to be critical cell killing lesions

Their repair is problematic and error-prone

24
Q

Give some examples of visible chromosomal aberration formation

A

Ring chromosomes

Di-centric chromosomes

25
Q

What is dose fractionation of radiotherapy?

A

Splitting the total dose into many single fractions

26
Q

Why is dose fractionation better?

A

Produces better tumour control for a given level of normal tissue toxicity than administration of a single large dose

Spares normal tissue by allowing for repair between doses

Allows better recovery of normal tissue than tumour tissue

Overcome tumour hypoxia

27
Q

Why does normal tissue recover more quickly than tumour tissue?

A

Tumour cells often arise due to deficiency in DNA repair. Therefore, normal cells can cope better because they ha e the full complement of repair systems where as tumour cells are compromised.

28
Q

Why does fractionation of dose overcome radioresistant hypoxia cells?

A

When doses are separated in reoxygenation of tumour cells can occur

29
Q

What does a multi-leaf collimator do?

A

Shapes the beam to the tumour volume, helping to spare normal tissue

30
Q

Why is multibeam therapy good?

A

Can superimpose the X-ray dose over the tumour-bearing region. Allows a high dose to the tumour volume while sparing adjacent tissues

31
Q

What is the Bragg peak?

A

A pronounced peak on the Bragg curve which plots the energy loss of ionising radiation during its travel through matter.

32
Q

When does the Bragg peak occur for protons? Why does is this better than X-rays?

A

Lose their energy immediately before the particles come to rest
Lower dose to surrounding tissue
So can deposit more energy with less damage to surrounding tissue.
X-rays are more penetrating so cannot be stopped at the target.

33
Q

Why is radiation a weaker carcinogen and mutagen compared to other chemical agents?

A

Because radiation normally induces cell death, not just damage

34
Q

How is nuclear medicine imaging done?

A

A radiopharmaceutical is taken orally, intravenously or internally
An external detector (gamma camera) captures and forms images from the radiation emitted

35
Q

How does nuclear imaging differ to traditional methods of imaging?

A

Shows the physiological function of the system being investigated as opposed to the anatomy

Generally more organ or tissue specific eg bone scan

36
Q

How is gamma radiation detected by cameras?

A

The photons pass into the instrument through collimators
The light spots created by gamma rays are picked up by photomultipliers and are amplified
They are sent through decoding circuits that establish the X and Y position of each spot
Signal is reconstructed as an image

37
Q

What does position emission tomography (PET) do?

A

Produces a 3-D image of functional processes of the body

38
Q

How does positron emission topography produce an image?

A

Pairs of gamma rays are emitted by a position-emitting radionuclide (tracer)
3-D images of tracer concentration within the body are constructed
Accomplished with a CT X-ray scan performed on the patient during the same session

39
Q

What is an example of a biologically active molecule used in PET?

A

FDG - a radioactive analogue of glucose

It’s concentration shows tissue metabolic activity in terms of regional glucose uptake

40
Q

List a few things that nuclear imaging scans can be used for?

A

Determine presence and spread of cancer
Localise lymph nodes before surgery in patients with breast cancer/melanoma
Kidney function
Heart flow and function
Respiratory and blood flow problems in lungs
Identify inflammation in the gall bladder
Evaluate bones for fractures, tumours, arthritis, infection
Identity bleeding in the bowel
Locate infection
Measure thyroid function
Investigate brain abnormalities eg seizures, memory loss, abnormalities in blood flow

41
Q

What are some examples of nuclear medicine therapies (unsealed source of RT)

A

Radioactive iodine - thyroid cancer
Radioactive antibodies to treat some lymphomas
Radioactive phosphorus for some blood disorders
Radioactive materials to reward painful tumour mets to bone

42
Q

What are the different aims of radiotherapy?

A

Intention to cure
Palliative care
-alleviate symptoms
-improve quality of life

Biology Of Cancer (13 decks)

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