Immobilisation

Question 1

Margins of treatment

Answer 1

o Allowance for spatial uncertainties (approx. 3-5mm) for radical plans
o Improved with immobilisation techniques and equipment
o Vastly Improved with IGRT

Question 2

Uncertainties

Answer 2

• Position of the beam relative to:
  o The equipment relative (limited by tool accuracy) (predictable)
  o To the patient (limited by patient movement) (unpredictable)
  o To the tumour volume (limited by patient movement) (unpredictable)

Question 3

Two main sources of uncertainty

Answer 3

-	Dosimetric
o	Inhomogeneities (bone blocking normal tissue, air pocket), dose calcs, machine output

• Geometry (Spatial)
  o Patient and Equipment Variables

Question 4

Spatial Uncertainties

Answer 4

• Patient Variable
  o Condition (size/weight, age/mobility, pain)
  o Cooperation, coherence, compliance
• Operational and Technique Variables
  o Patient positioning, marks, documentation
   Preparation, Execution and accuracy

Question 5

Two types of error

Answer 5

• Random Errors (specific to operator and/or patient)

- Systematic Errors (inherent to a system of operation)

Question 6

Organ immobilisation

Answer 6

• Some organs move or change size
• Can apply measure to minimise this
  o Bladder – fill/empty
  o Rectal filling

Question 7

Marks and Tattoos

Answer 7

• Beware of loose skin – it moves
• Use obvious and proximal landmarks
• Make visible

Question 8

Strategies and equipment for head and neck

Answer 8

o Supine, Head Rest, Knees raised (bolster)
o Immobilisation  Shell and Shell Board
o Optional  Handgrips, mouthpiece, bite block, external frames

Question 9

Strategies and equipment for breast

Answer 9

o Supine (incline, arms above head), Head rest (chin raised), Knees Raised (bolster)
o Immobilisation  breast board, arm cuffs, bum-stopper
o Optional  Prone, breast shell, tape

Question 10

Strategies and equipment for chest and abdomen

Answer 10

o	Supine (straight and level), Headrest, Knees Raised (bolster), Chest Board for indexing and arm immobilisation 
o	Optional  Prone (post spine), Shell, Incline, Vac-bag

Question 11

Strategies and equipment for CNS

Answer 11

o	Supine (straight and level), Headrest, Shell, Vac-bag, Arms by Side, Knees Raised (bolster) 
o	Optional  Prone, Sedation (for children)

Question 12

Strategies and equipment for pelvis

Answer 12

o	Supine (Straight and level), Arms on chest, Headrest, Knee’s bolster (indexed), Foot-stocks (indexed) 
o	Optional  Prone, Belly board, Shell

Question 13

Strategies and equipment for Limbs

Answer 13

o Supine, Varies greatly with site

o Optional  Vac bags, immobilisation devices, shells

Question 14

Common Anatomical Landmarks

Answer 14

o Midline
o Ear: ITN, STN, ATN, EAM
o Eye: Medial and Lateral Canthus
o Mandible: angle of mandible, base of skull
o Nose: Nasal septum
o Chin: Oral Commissures, Vermillion Borders