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Intro to Mphys > Radiotherapy Intro > Flashcards

Radiotherapy Intro Flashcards

1
Q

Describe the 3 stages of cancer development

A
  1. Initiation -
  2. Promotion
  3. Progression - when metastesis start to occur
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2
Q

What are the main treatments for cancer

A

Surgery, chemotherapy (inhibits cancer cell reproduction), hormone therapy (block or lower hormones), Immunotherapy (boost natural defences), Radiotherapy (ionising radiation to kill cancer cells.

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3
Q

How effective has Radiotherapy been for breast cancer recurrsnce and death. and prostate cancer

A

Recurrance is halved and deaths have drastically reduced.

Prostate cancer results are comparable to surgery

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4
Q

Describe / draw the rate of cell growths for tumour and normal tissue. Also draw curves for the response to radiation of these tissues

A

Exponential growth of both groups with tumour out performing.

Both exponentially decreasing. At low doses normal tissue recovers better as dose increases this switches. This leaves a window of opportunity at the lower doses to treat affected areas.

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5
Q

Cell recovery and fractionation - graph

A

Wave like pattern, but normal tissue able to recovery after each treatment.

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6
Q

Typical prescribed dose for breast and prostate treatments

A

breast - 40Gy in 15 daily fractions
Prostate - 74 Gy in 37 fractions

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7
Q

How much would a treatment of 74Gy in a single dose raise the temperature of the prostate gland. assume a mass of 50g

A

1Gy = 1J/kg
1 Cal = 4.184 J
1 cal raises 1g of water by 1 degree.
0.02 - look at lecture video

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8
Q

What types of radiation are used?

A

Photons
Electrons
Protons
Neutrons
other heavy ions

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9
Q

What types of interactions ocurr

A

Photoelectric absorption
Compton Scatter
Pair production

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10
Q

How doe penetration vary with energy of radiation

A

Penetration increases

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11
Q

What are the two types of treatment available

A

Radical - curatvie
Palliative - pain releif

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12
Q

How might treatment be altered to treat
1. Skin
2. Tumours a few cm deep
3. Deep tumours
4. Whole body

A

Beam angle, choise of treatment machine, modality and energy.

  1. Kv unit
  2. MeV electrons (linac)
  3. Mv photons (linac)
  4. photons or electrons (linac)
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13
Q

What are the key stages of the patient pathway

A
  1. Pre treatment simulation (CT scan) - patient positioning and immobilisation)
  2. Planning (Localising tumour volume, organs at risk, determination of optimal beam arrangement, resulting dose evaluation)
  3. Verification (CBCT acquired before treatment to confirm patient positioning
  4. Delivery s
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14
Q

How is a beam modified and what effect dose this have

A

Beams can be modified with a wedge or MLC. This changes the dose distribution to the patient. Often changed depending on thickness of tissues passing through and to morph beam shape to tumour shape

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15
Q

Describe the working principles of a linac - use a diagram to help

A

Electron source, wave guide, bending magnet and collimation.

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16
Q

How does an electron gun work

A

Heats up and emits electrons by thermionic emission

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17
Q

How does the wave guide work

A

Micorwave wave guide. Is an electric field within a vacuum which accelerates electrons within a ‘waveguide’.

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18
Q

How are the photons created

A

Electron beam comes into contact with a tungston target and X-rays are generated. A range of energies are generated therefore requiring filtering. Lots of heat produced therefore cooled with water and heat exchanger.

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19
Q

Draw the graph of penertration of electrons and photons

A

….

20
Q

Describe breifly Cyberknife

A

Small linac with a robotic arm allowing of 6 degrees of motion. Has real time imaging. can optomise beam path

21
Q

Tomotherapy

A

Similar to CT scanner in apprearance. Helical pattern of delivery

22
Q

Gamma knife.

A

Radiosurgery for brain tumours. Head is positioned inside and beams can be delivered from diffrerent angles. Multiple lesions can be treated at the same time.

23
Q

Other special techniques include TBI and total skin electron beam therapy. what might the be use for

A

TBI, bone marrow treatment for leukemia. often utilises a spoiler, to reduce build up of dose at the skin.

  1. Covering large areas of effected skin.
24
Q

How does electron beam therapy differ

A

uses electrons with energies 4-25Mev. it has a shorter range than photons for the treatment of superficial lesions

25
Q

what is the penetration of a proton in proton beam therapy

A

5-10cm. there is a narrow bragg peak. bragg peak can be spread though

26
Q

What is brachytherapy

A

Delivery of radiation therapy using sealed sources which are placed as close as possible to the site to be treated. either for cancers in a body cavity (Intracavity) using a catheter or needle into or close to tissue (Interstitial). Intraluminal - oesophogus / bronchus. trachea.

27
Q

Why is MRI good for treatment planning

A

High soft tissue contrast
Non ionising treatment planning, functional imaging

28
Q

benefits and challenges of MRI for treatment verification

A

Benefits - Soft tissue contrast, real-time imaging, non-ionising radiation, functional imaging.

Challeneges - MRI performance / distortion, electron density information, Linac operation / dose distribution in magnetic field, staffing workflow of adaptive planning. and tatooless setup.

29
Q

What is the workflow for treatments

A

scan - outline - plan - check - prepare - treat - treat again.

Adaptvie readiotherapy is only different as this is conducted every fraction with a re-scan.

30
Q

What are the 3 main points in automated treatment planning

A

Delineation (organs at risk and tumour) - Optimisation (Beam paths VMAT)- Prediction (dose distributions)

31
Q

How is SABR different

A

Delivers high doses in 1-5 fractions.

32
Q

What are the three primary points to consider when combining radiotherapy and immunotherapy

A
  1. Radiotherapy kills cancer cells which release molecules that might alert the immune system.
  2. Immune cells pick-up these signals, which could help target the tumour.
  3. Comvining this with immunotherapy could make the immune attack more effective.

Known as the abscopal effect

33
Q

define absorbed, equivalent and effective dose

A

Absorbed Dose - Energy absorbed by an irradiated sample of matter (Gy). Energy absorbed per unit mass. J/Kg.

Equivalent - Biological effect for that specific type of radiation (Sv)

Effective - Biological weighting factor added for a specific type of tissue depending on it’s radiosensitivity. (Sv)

34
Q

Define Linear energy Transfer

A

A measure of energy transferred by ionising particle to traversed material. KeV/m

35
Q

Give examples of radiation with low and high LET

A

Low - C-rays, gamma-rays. Energy is distributed homogeneously.

High - alpha beta particles and neutrons. Energy is distributed inhomogeneously.

36
Q

How does LET translate to RBE

A

RBE - relative biological effectiveness. High LET has a higher RBE.

This means that the same dose by a different type of radiation has a different biological effect.

37
Q

Weighting factors of 0.12, 0.08, 0.04 and 0.01 apply to which tissues

A

0.12 - Bone marrow, colon, lung, stomch, breast

0.08 - Gonads

0.04 - Bladder, Oesophogus, liver, thyroid

0.01 - Bone surface, brain, salivery glands, skin

38
Q

What is meant by Committed effective dose

A

The sum of the produts of the committed organ or tissue0equivalent doses, HT(tao) and the appropriate tissue weighting facotrs (wT), where tao is the integration time in years following intake.

39
Q

Main differences between direct and indirect action. with regards to radiation damage

A

Direct - damange to the sugar phosphate backbone of the DNA strand. Causing a brake therefore cell death.

Indirect - Absorption in water leads to a chemical reaction. Free radicals combine to form new species toxic to the cell.

40
Q

What differences do Low let vs High LET radiation cause in DNA strands

A

Low LET radiation produces localised clusters of ioinisations within single electron tracks.

High LET radiation produces a larger number of ionisations that are closer together.

41
Q

What are the three ways that radiation damage are manifested

A

Somatic: Occurs in somatic cells which are all the cells in the body other than reproductive cells

Genetic damage: changes in the genetic material of cells due to exposure to radiation

Teratogenic damage: the development of birth defects due to exposure to radiation during pregnancy

42
Q

What are the two primary categories of radiation damage amifestation

A

Deterministic - Threshold of radiation above which damage ad symptoms will occur. Severity increases with exposure

Stochastic - No threshold, probabilistic. more radiation = higher likliehood of effects happening.

43
Q

Name some deterministic effects

A

Erythema: 1-24 hours after irradiation of about 3-5Gy.

Alopecia: 5Gy is reversible; 20Gy is irreversable.

Pigmentation: reversable, appears 8 days after irradiation.

Dry or moist desquamation traduces epidermal hypoplasia 20Gy

Delayed effects: teleangiectasia fibrosis.

44
Q

3 stages of cancer production

A

Initiation

Tumour progression

Malignant progression

45
Q

What are the cardiovascular effects of radiation

A

Radiation exposure can contribute through microvascular damage to myocardium. leavig fatty deposits on the insides of vessels. >0.5Gy latency period 5-20 years.

46
Q
A

Intro to Mphys (10 decks)

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