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MED 107- MEDICAL PHYSICS II > 65. RADIOTHERAPY: TREATMENT PLANNING > Flashcards

65. RADIOTHERAPY: TREATMENT PLANNING Flashcards

1
Q
  1. What does the Treatment Plan describe?
A
  • it describes the dose distribution
  • when one or more radiation beams converge on the
    treatment volume

NB:
- it describes this graphically

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2
Q
  1. What is the Treatment Volume?
A
  • this is the volume which has to be treated

EXAMPLE:
- tumour
- cyst
- tissue

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3
Q
  1. What is the Treated Volume?
A
  • this is the volume which is actually treated
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4
Q
  1. What 3 volumes do International reports give definitions of?
A
  1. Planning Target Volume (PVT)
  2. Clinical Tumour Volume (CTV)
  3. Gross Tumour volume (GTV)
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5
Q
  1. What are the typical criteria for judging how good a Dose Distribution is?
A
  1. THE DOSE THROUGHOUT THE TREATMENT VOLUME
    - should be uniform
    - to about plus-minus 5%
  2. THE TREATED VOLUME
    - should be nearly as possible
    - to the Treatment (PTV) Volume
  3. THE DOSE TO THE TREATED VOLUME
    • should exceed the dose elsewhere
    • by at least 20%
  4. THE DOSE TO SENSITIVE SITES
    - should be below the tolerance dose of those sites
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6
Q
  1. What are some examples of Sensitive Sites?
A
  • eyes
  • spinal cord
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7
Q
  1. How do we usually satisfy the criteria for the Dose Distribution?
A
  • we use several beams
  • they are as small as possible
  • they enter the patient as close to the treatment volume
    as possible
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8
Q
  1. What is LINAC planning?
A
  • this is when a CT for image guided radiotherapy is
    taken
  • the targets are then defined
  • the treatment is then planned
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9
Q
  1. What role does the Medical Physicist play in LINAC planning?
A
  • they choose the radiation beam direction
  • they choose the beam type
  • they choose the beam energy
  • they conform the radiation for each beam
  • they execute a treatment plan simulation
  • they verify the plan
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10
Q
  1. What happens once the Medical Physicist has verified the plan?
A
  • a physician will also verify it
  • then they will approve it for use
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11
Q
  1. What is this an image of?
A
  • this is the Beam Application of LINAC Planning
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12
Q
  1. What is this an image of?
A
  • this is the Beam Energy of LINAC Planning
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13
Q
  1. Due to our skin being curved, how does the beam enter the skin?
A
  • it has to enter the skin at any other angle other than
    90°
  • this alters the Dose Distribution
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14
Q
  1. How do we solve the problem of the beam entering the skin at an angle that is not 90°?
A
  1. We correct the Curvature of the skin
  2. We correct the Distribution
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15
Q
  1. What situation can cause skin to be built up?
A
  • the lack of a skin-sparing effect at low energies
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16
Q
  1. What happens when the dose makes use of a Tissue-Equivalent Bolus?
A
  • this gives a surface that is at a 90° to the beam
17
Q
  1. What is a Bolus?
A
  • this is a material
  • it helps to increase the skin dose for photo beams
18
Q
  1. When do we not use a Bolus?
A
  • when we are dealing with High Energies
  • we use mathematical calculations instead
19
Q
  1. Other than using a Bolus, how else can we correct the Isodose Distribution?
A
  • we can use a tissue compensator
  • we place this in the beam remote from the skin
20
Q
  1. What is a Beam Remote?
A
  • this is a suitably shaped attenuator
  • it compensates for the missing attenuation of the
    tissue
21
Q
  1. What do we do when we have to treat a large volume that is close to the surface?
A
  • we alter the Isodose distribution
  • this is done by wedge-shaped compensators
22
Q
  1. What effect will the edges have on the beam?
A
  • they will attenuate it more at the thick end of the beam
  • they will tilt the Isodose Curve
23
Q
  1. What do we do with the beam intensities in a LINAC Planning situation?
A
  • we optimise them
  • this achieves the best coverage of the tumour
  • this saves the healthy tissue
24
Q
  1. What machinery do we use to spare sensitive organs?
A
  • we use Collimators
25
Q
  1. Where do we plot the Isodose curves?
A
  • we plot them on the anatomy

MED 107- MEDICAL PHYSICS II (108 decks)

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