Wk 3 - Protons

Question 1

range shifter

Answer 1

• Tissue equivalent energy absorber of varying thickness
• Used when energies of machine cannot get low enough to treat
• ‘Air gap’ is distance to patient

Question 2

snout

Answer 2

Fixed or telescopic accessory
that dictates the maximum field
size

Question 3

SFUD + sites

Answer 3

single field uniform dose
where the spot position and weights of each proton field are optimised individually

• ‘3D conventional’ equivalent
• each field achieves a uniform dose over target
  
  • fields are decoupled
  • more robust
  • less opportunity for complex dosimetry

lung, prostate, tumours far from OARs

Question 4

MFO + sites

Answer 4

multi-field optimiser
where the spots from all fields are optimised together generating a highly conformal dose distribution

• ‘IMRT’ equivalent
• each field delivers a heterogenous dose to the target
  
  • fields are strongly coupled
  • less robust
  • more opportunity for complex dosimetry

head and neck, multiple levels, complex tumours

Question 5

proton beam placement considerations

Answer 5

Beam placement is key
- Usually only 1- 4 beams
- Homogenous path to target
- Entry through well immobilised
anatomy

Question 6

tasks which are performed by the planner include

Answer 6

• choice of technique
• selection of beam techniques
• definition of plan objectives
• selection of beam modifiers (eg. rangeshifter)

Question 7

TPS will perform the these tasks

Answer 7

• energy layers
• spot placement
• spot weight

Question 8

spot placement

Answer 8

defines the locations of all spots in each energy layer, distributing the spots so that they cover the entire volume of the target. within each layer, spots are arranged in either a square or hexagonal grid, and the TPS defines the order in which spots are delivered

Question 9

spot weight

Answer 9

defines the dose to be delivered to each spot in terms of the number of MUs. this relates to the charge measured by the MU ionisation chamber which is the part of the delivery system and is located within the nozzle. the number of MUs can be directly related to the delivered dose via the calibration of the delivery system

Question 10

Describe the 4 steps of pencil beam scanning

Answer 10

1. Protons accelerated until they reach a certain energy
2. Transported through a beamline to the machine
3. Directed toward the patient with magnets
4. Protons spot dose within the patient at the desired depth