65. RADIOTHERAPY: TREATMENT PLANNING Flashcards
1
Q
- 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
2
Q
- What is the Treatment Volume?
A
- this is the volume which has to be treated
EXAMPLE:
- tumour
- cyst
- tissue
3
Q
- What is the Treated Volume?
A
- this is the volume which is actually treated
4
Q
- What 3 volumes do International reports give definitions of?
A
- Planning Target Volume (PVT)
- Clinical Tumour Volume (CTV)
- Gross Tumour volume (GTV)
5
Q
- What are the typical criteria for judging how good a Dose Distribution is?
A
- THE DOSE THROUGHOUT THE TREATMENT VOLUME
- should be uniform
- to about plus-minus 5% - THE TREATED VOLUME
- should be nearly as possible
- to the Treatment (PTV) Volume - THE DOSE TO THE TREATED VOLUME
- should exceed the dose elsewhere
- by at least 20%
- THE DOSE TO SENSITIVE SITES
- should be below the tolerance dose of those sites
6
Q
- What are some examples of Sensitive Sites?
A
- eyes
- spinal cord
7
Q
- 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
8
Q
- 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
9
Q
- 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
10
Q
- What happens once the Medical Physicist has verified the plan?
A
- a physician will also verify it
- then they will approve it for use
11
Q
- What is this an image of?
A
- this is the Beam Application of LINAC Planning
12
Q
- What is this an image of?
A
- this is the Beam Energy of LINAC Planning
13
Q
- 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
14
Q
- How do we solve the problem of the beam entering the skin at an angle that is not 90°?
A
- We correct the Curvature of the skin
- We correct the Distribution
15
Q
- What situation can cause skin to be built up?
A
- the lack of a skin-sparing effect at low energies
16
Q
- 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
- What is a Bolus?
A
- this is a material
- it helps to increase the skin dose for photo beams
18
Q
- When do we not use a Bolus?
A
- when we are dealing with High Energies
- we use mathematical calculations instead
19
Q
- 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
- What is a Beam Remote?
A
- this is a suitably shaped attenuator
- it compensates for the missing attenuation of the
tissue
21
Q
- 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
- 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
- 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
- What machinery do we use to spare sensitive organs?
A
- we use Collimators
25
Q
- Where do we plot the Isodose curves?
A
- we plot them on the anatomy
