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Biophysics 2 (Theory) > 9. Radiation therapy: linear energy transfer, penetration depth, Bragg-peak. Devices for radiation therapy. ALARA principle, dose limits. > Flashcards

9. Radiation therapy: linear energy transfer, penetration depth, Bragg-peak. Devices for radiation therapy. ALARA principle, dose limits. Flashcards

1
Q

What is radiation therapy?

A

A medical intervention, where the pathological tissues are destroyed by ionizing radiation

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2
Q

What is the aim of radiation theory

A

to deliver a curative dose of irradiation to a defined tumor volume with as minimal damage as possible to surrounding healthy tissue.

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3
Q

What are the 6 well-known ionizing radiations used in radiotherapy?

A
  1. Alpha radiation
  2. Beta radiation
  3. Electron radiation
  4. Gamma radiation
  5. X-ray
  6. Proton radiation
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4
Q

Consequences of the absorption of ionizing radiation.

What are they? (3)

A
  1. Physical events
  2. Chemical reactions
  3. Biological consequences
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5
Q

Consequences of the absorption of ionizing radiation. - 1. Physical event

What does The amount of secondary ionization depend on?

A

on the material

→ it can be up to 10 times the amount of primary ionization.

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6
Q

Consequences of the absorption of ionizing radiation.

Describe the physical events

A

Using direct or indirect ionization

  • Charged particles interact strongly and ionize directly
  • Neutral particle;es interact less, ionize directly and penetrate farther
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7
Q

Consequences of the absorption of ionizing radiation.

Describe the chemical; events

A

Cell death, death of living system

Carcinogenesis, genetic transformation

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8
Q

Consequences of the absorption of ionizing radiation.

Describe the biological events

A

Direct or indirect effects occur

  • Direct effect - Direct ionization of the macromolecules
  • Indirect effect - Reactive ions (e.g. OH-) and/or radicals (e.g. *OH) are generated mainly from water molecules.
    → Reactive species induce damages in macromolecules and membrane structures.
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9
Q

3 approaches for radiotherapy

A
  1. Palliative radiotherapy
  2. Radical radiotherapy
  3. Adjuvant treatment
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10
Q

Purpose of Palliative radiotherapy. (+ examples)

A

to reduce pain and address acute symptoms

– e.g. bone metastasis, spinal cord compression etc.,

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11
Q

Purpose of Radical radiotherapy. (+ examples)

A

primary modality for cure

– e.g. head and neck tumours

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12
Q

Purpose of Adjuvant radiotherapy. (+ examples)

A

an additional cancer treatment given after the primary treatment such as surgery

→

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13
Q

What is Linear ion density?

A

the amount of n ion pairs produced on a path of length l

→ give the quantity n/l

→ characterize ionizing power

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14
Q

What is LET (Linear Energy Transfer)?

A

the energy transferred to the material surrounding the particle track, by means of secondary electrons

→ (nEion pair/l) → i.e, the product of the linear ion density and the energy necessary for creating an ion pair

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15
Q

Characteristics of α-radiation in radiotherapy

A

Internally deposited radioactivity

High ionizing power → high biological effect

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16
Q

How can α-radiation be used in radiotherapy

A

Internally deposited radioactivity

  • α-radiation reach only the body surface → have to introduce the isotope itself into the target
  • The isotope is bound to a carrier molecule (e.g, antibody) → reach the tumor cells ASAP → exerting damaging effects
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17
Q

Characteristics of β- radiation in radiotherapy

A
  • Internally seeded radioactivity
  • Particle energy is not optimal
  • continuous energy spectrum
  • typical energy: few MeV
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18
Q

Disadvantages of β- radiation in radiotherapy

A
  • typical energy: few MeV → not penetrating deeper
  • continuous spectrum
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19
Q

Why is continuous spectrum a disadvantag of β- radiation in radiotherapy

A
  • One portion of electrons has energy that is below the average → readily absorbed
  • Other part has above-average energy → can penetrate deeper
20
Q

Characteristics of electron radiation in radiotherapy

A
  • accelerated electron
  • production: linear accelerator
  • Efficient distance

→ can be used for treatment of superficial tumours

21
Q

2 differences between β- radiation and electron radiation

A

β- radiation VS. electron radiation

  • β- radiation - energy is determined by the isotope and its decay
  • electron radiation - energy can be controlled
  • β- radiation - continuous energy spectrum
  • electron radiation - energy spectrum is dismissed → each accelerated electron has the same energy
22
Q

How can β- radiation and electron radiation be used together?

A

Drawbacks of β- radiation can be useful accelerated electrons with some kind of particle accelerator

23
Q

Why is electron radiation suitable for treatment of superficial tumors?

A
  • The energy loss of accelerated electrons is hardly changed until a given penetration depth
24
Q

What is dose-depth?

A

The distribution of absorbed dose in the direction of radiation

25
Q

Describe gamma radiation in radiotherapy

A
  • Having an indirect ionizing effect

→ Site of absorption is different from site of ionization which is also site of damage

  • Penetration distance is energy dependent
26
Q

Describe Electron PDD (percentage depth dose ) curves of gamma radiation

A
  • PDD curves at voltages (see X-ray) and various photon energies
27
Q

Describe gamma knife (radiotherapy)

A
  • Focus multiple radiation sources onto a target from different directions simultaneously

→ The radiation isocenter is the point in space where radiation beams intersect

28
Q

Describe characteristics of X ray used in radiotherapy

A

The X-rays are generated by a linear accelerator .

Few MeV photon energy.

29
Q

Describe characteristics of X ray used in radiotherapy

A

The X-rays are generated by a linear accelerator .

Few MeV photon energy.

30
Q

Describe characteristics of proton radiation used in radiotherapy

A
  • A beam of protons accelerated by a particle accelerator
  • Would be ideal, but very expensive!
31
Q

Describe characteristics of proton radiation used in radiotherapy

A

It depends on velocity → protons ionize differently along different points of their path

32
Q

What is relative depth-dose curve?

A

The curve of the dose distribution in the direction of spreading of the radiation

33
Q

What is Bragg peak?

A

The number of generated ion-pairs gives such a peak at the end of the beam

→ this beam is where the proton slowed down and has concentrated ionization

34
Q

Describe characteristics of NEUTRON radiation used in radiotherapy

A
  • collision of high energy protons (66 MeV) into berillium target ( p(66) +Be) → Neutrons induce nuclear reactions.
  • High LET
35
Q

Sources of natural background OF RADIATION

A
  1. cosmic radiatiom
  2. radon
  3. potassium:
36
Q

How can cosmic ray contribute to dose rate?

A

Cosmic ray contributions to dose rate as the function of the altitude

37
Q

3 aims of radiation protection

A
  1. Prevention from deterministic effects (except in radiotherapy those that are intentionally produced)
  2. Keeping the occupational risk of the users of the sources at the level of occupational risk of other professionals.
  3. Keeping the public risk from ionising radiation sources at the level of public risk of other civilization related harms.
38
Q

3 principles of radiation protection

A
  1. Optimization
  2. Justification
  3. Limitation
39
Q

3 principles of radiation protection

What is optimization?

A

All exposures should be kept As Low As Reasonable Achievable (ALARA)

40
Q

3 principles of radiation protection

What is ALARA principle?

A

All exposures should be kept As Low As Reasonable Achievable (ALARA)

X : cost of radiation protection

Y : cost of treatment
X+Y: total cost

→ Optimum is the minimum

41
Q

3 devices that can be used for Detection of particles

A

• Cloud chamber

  • Spark chamber
  • Bubble chamber
42
Q

What is a cloud chamber?

A

A particle detector consists of a sealed environment containing a supersaturated vapour of water or alcohol.

43
Q

What is a spark chamber?

A

A particle detector useful for the investigation of subatomic particles in high-energy particle physics.

It consists of a series of thin metal plates parallel to each other, separated by small gaps, and enclosed in a container filled with neon or another inert gas.

44
Q

What is a Bubble chamber
?

A

– particle detector

– superheated transparent liquid (H2, Ar, Xe)

– entire chamber is subject to a constant magnetic field

45
Q

3 principles of radiation protection

What does Justification principle state?

A

no practice shall be adapted unless it produces a positive net benefit

46
Q

3 principles of radiation protection

What does LMITATIOHNprinciple state?

A

the effective dose (E) to individuals shall not exceed the limits recommended by the ICRP (maximum permitted doses)

Biophysics 2 (Theory) (13 decks)

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