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Planning > Biologically Optimisef RT TP > Flashcards

Biologically Optimisef RT TP Flashcards

1
Q

What is the indirect action of cell damage by radiation?

A
  1. primary photon interaction producing high energy electrons
  2. high energy electrons in moving through the tissue produce free radicals in water
  3. free radicals may produce change in DNA from breakage of chemical bonds
  4. Changed in chemical bonds result in biological effect
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2
Q

Physical vs Biological planning

A
  • currently used physical quantities as surragotes for biological response
  • better approach to use bioloigcal indices ot more directly reflect the clinical goals
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3
Q

What is biologically guided RT?

A
  • use individual patient biological repsonse of tumour and NTT to design dose distribution
  • tumour and NTT radiosentivity, oxygenation status and profliferation rate
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4
Q

What is biological based TP?

A
  • use feedback from biological response models
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5
Q

What is the dose reponse model?

A
  • biological cell survival models are required for tumours and normal tissue
  • model predict observations seen in clinical dose repsonse data
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6
Q

What is the generalised equivalent uniform dose?

A
  • the uniform dose that would yield the same radiobiological effect as the non-uniform dose
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7
Q

What is the linear quadratic model?

A
  • used to describe the cell surivial curve assuming there are two compenents to cell kill
  • the ratio a/b gives the dose at which the linear and quadratic components of cell kill are equal
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8
Q

What does the a describe?

A
  • initial slope of surival curve
  • respresents the intrinsic radiosensitivity of the cell
  • non-reparable type of cell damage
  • linearly dependent on dose
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9
Q

What does the b describe?

A
  • the curvature of the cell survival curve
  • repariable type of cell damage with time
  • responsible for the dose/fraction variable
  • proportional to the sqaure of the dose
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10
Q

What is biologically equivalent dose?

A
  • fractionation schemes for which BED is equal will be equally effective biologically
  • clinical a/b only accounts for repair
  • K accounts for accelerated repopulation
  • LQ model allows comparison of different fractionation scheduales
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11
Q

What is early dose responding?

A
  • occurs immediately or during RT
  • cell depletion within rapdily dividing cells
  • e.g. skin, muscosal layer of gut causing pain and discomfort
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12
Q

What is late dose resonding?

A
  • start 6-12 months after RT
  • cell depletion within slowly dividing cells
    e. g. spinal cord and kidneys casuinng irreversible symtoms
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13
Q

What are the general early and late effect tissues?

A
  • early: most tumours, large a/b (10Gy) and a dominates at low dose
  • late: normal tissue, small a/b (2Gy) and b has influence at low dose
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14
Q

What are the 5 R’s of RT?

A
  1. radiosensitivity
  2. repair
  3. repopulation
  4. redistribution
  5. reoxygenation
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15
Q

What is radiosensitivity?

A
  • cells have different radiosensitivies
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16
Q

What is repair?

A
  • cells can repair sub-lethal radiation damage
17
Q

What is repopulation?

A
  • cells repopulated during fractionated RT
18
Q

What is redistribution?

A
  • in proliferating cell population through the cell cylce increases the cell kill in the fraction therapy relatve to single fraction
19
Q

What is reoxygenation?

A
  • of hypoxic cells during fractionated RT makes them more sensitive to subsqent dose
20
Q

What is the radiobiological rationale for fractionation?

A
  • dividing dose spares normal tissue thorugh a repair of sublethal damage between fractions and repopulation of cells
  • fraction increases tumour damage through reoxygenation and redistribution
21
Q

What is the sensitivity to fraction size?

A
  • rapidly prlifering cells (high a/b) and not sensitive to change in fraction size ro dose rate
  • slowly proliferating cells (low a/b) are sensitive to dose/fraction and have plenty of repair capability
22
Q

What size of fractionation are late responding tissue sensitive too?

A
  • large
23
Q

What is an a/b Gy example of early reacting tissue?

A
  • skin: 9-12
  • colon: 9-11
  • testis: 12-13
  • mucosa: 9-10
24
Q

What is an a/b Gy example of late reacting tissue?

A
  • kidney: 2-2.4
  • rectum: 2.5-5
  • lung: 2.7-4
  • bladder: 3-7
  • SC: 1.8
  • Brainstem: 2.2
25
Q

What is an a/b Gy exmaple of tumours?

A
  • larynx: 15-35
  • melanoma: 0.6
  • prostate: 1.5
26
Q

What is the best fractionation for prostate?

A
  • fewer and larger fractions due to low a/b (1.5)

- hypofractionation increases dose per fraction minimising tumour cell proliferation during course of RT

Planning (8 decks)

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