CNS Flashcards
CNS - Moving Junctions
• Feathering technique used to even out cold and hot spots
- TPS modulates dose so it helps reduce chances
of error
• It changes field size daily
• Must be recorded
Floor turn (non-coplanar)
- A traditional technique where floor is moved 5-6 degrees
* Used for head and neck (brain field) to achieve OAR tolerances BUT will affect remaining spine fields
Prone vs Supine
Prone – NOT STANDARD
• Better access for spine
• Palpate for set-up/ field placement
• Refer to skin markings for junction assessment
• Has better general accuracy with reduced margins
Supine – STANDARD with technology development
• Paeds are more comfortable and feel more secure
• Better access to anaesthesia
What are the three main treatment modalities for PNET?
- surgery
- craniospinal irradiation
- adjuvant chemotherapy
When is surgery used for PNET?
- essential as first line treatment
- should be as complete as possible without causing disability
How soon after surgery should CNS RT commence?
- as soon as recovery permits (2-3 weeks) because of risk of tumour seeding
- post foassa or primary tumour site to be boosted after whole CNS treatment
When should chemo be used?
- concurrent chemo followed by adjuvant mutli agent therapy for 1 year has proven improved survival
If child is under 3 is RT used?
- usually delayed because of associated risks, but control rates are higher when radiation is used
What is the typical RT fields for CNS treatment?
- lateral skull fields
- direct post fields to treat spine as far inf as the fourth sacral formina and including the sacral nerve roots
- number of spine fields depends on spine length
What is the technique for the lateral skull fields?
- isocentric and collimated to match the divergent sup edge of the adjoining posterior spine field at mid sagittal plane
- inf border of skull field will match the sup border of the spine field at midline on the post skin surface
- to get complete match need to rotate the floor 3-5 degrees or set skull inf jaw to zero if head is small enough
What is the CNS brain technique with VMAT?
- 1-2 arcs
- an extra arc using floor turn to achieve OAR may be needed
What are the important OAR to consider in skull fields?
- optic chiasm and nerves (54Gy), globes (45Gy)
- cochlea (20-30Gy)
- brainstem (54Gy)
- hypothalamus and pituitary dose to be minimised
What are some considerations for the lateral skull fields?
- inf border to finish C4-5
- primary site is to be posted so junction region should be well inf of this as there will be hot spot at the junction
- limiting factor is shoulder position
- mandible/chin position needs to be considered (divergent edge of upper spine but don’t want so up that neck folds are formed otherwise skin reaction)
