Target Volume Localisation

Question 1

Steps of treatment planning process (x10)

Answer 1

1. Immobilisation
2. Tumour localisation
3. Virtual representation of patient
4. Selection of treatmen geometry
5. Optimisation of dose distribution
6. Calculation of Dose and MU required
7. Independent Dose verification
8. Documentation of treatent information
9. Verification of treatent set-up
10. Treatment Delivery

Question 2

Purpose of immobilisation (x2)

Answer 2

1. Reproducible patient position
2. Appropriate position for treatment and delivery geometry

Question 3

6 Desireable characteristics of Immobilisation

Answer 3

1. Easy to use
2. Easy to produce
3. Patient comfort
4. resistance to bending and stretching
5. Minimal attenuation of beam
6. Minimal imgaing artefacts

Question 4

Purpose of Tumour Localisation

Answer 4

• Identify gross tumor volume (GTV)
• Identify multi-focal disease or nodes

Question 5

6 Methods of localisation

Answer 5

1. Direct visualisation - look or by touch
2. Simulator - x-ray set on gantry, outdated now
3. CT - god for lungs, not enough soft tissue contrast for others
4. MRI - Soft tissue contrast and differentiation of pathology
5. Ultrasound - prostate and bladder, brachy
6. PET-CT - metabolic imaging, needs to be combined with CT for anatomical information

Question 6

Different ways to represent a patient:

Answer 6

• separation - 1D patient is box of water, only appropriate for parallel-opposed pairs, measured along central axis
• Manual contour - 2D, wire used to transfer axial contour ro paper.
• CT slice - 2D
• CT Volume - 3D, multiple slices, most modern planning systems.

Question 7

positives & negatives of CT Volume patient representation:

Answer 7

Positives

• Geometric accuracy
• HU to map electron density
• Good res
• Good bone contrast
• Image fusion and data transfer
• Image manipulation (window and level)

Negatives

• Poor soft-tissue contrast

Question 8

What do you need to localise a tumour for RT treatment?

Answer 8

1. Patient
2. Imaging equipment
3. Immobilisation
4. Method of patient marking for allignment in treatment room
5. Software application to define treatment geometry
6. Method of dose calculation