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CSB092 > CNS > Flashcards

CNS Flashcards

1
Q

What are the two most common CNS tumours?

A

known as primitive neuroectodermal tumours

  • pinealoblastoma
  • medulloblastoma
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2
Q

What is the metastasis of PNET?

A
  • highly invasive
  • spread rapidly through CSF
  • 20% have spread to SC before diagnosis
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3
Q

Where do medulloblastomas arise?

A
  • in cerebrellum or posterior fossa
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4
Q

What is the most common and rare type of PNET?

A

Common - medulloblastoma (20% of all paediatric brain tumours)
Rare - pinealoblastoma

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5
Q

What is the epidemiology of medulloblastoma?

A
  • rare in adults: most occur before 16

- more common in males (M:F, 2:1)

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6
Q

What causes the signs and symptoms for PNET?

A
  • associated with raised intracranial pressure which can be caused by a blockage of the ventricles leading to a build up of CSF
  • local swelling around the tumour itself
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7
Q

What are the signs and symptoms of medulloblastoma?

A
  • headache
  • vomiting
  • irritability
  • problems with motor function
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8
Q

What are the signs and symptoms of glioblastoma?

A
  • headaches
  • seizures
  • vomitting
  • trouble speaking
  • blurred vision
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9
Q

What classifies an average risk patient?

A
  • older then 3
  • minimal or no residual tumour (<1.5cm max diameter)
  • no evidence of metastatic spread
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10
Q

What classifies a high risk patient

A
  • significant residual disease (>1.5cm max diameter)
  • evidence of metastatic disease
  • under 3
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11
Q

What are the three main treatment modalities for PNET?

A
  • surgery
  • craniospinal irradiation
  • adjuvant chemotherapy
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12
Q

When is surgery used for PNET?

A
  • essential as first line treatment

- should be as complete as possible without causing disability

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13
Q

How soon after surgery should CNS RT commence?

A
  • 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
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14
Q

When should chemo be used?

A
  • concurrent chemo followed by adjuvant mutli agent therapy for 1 year has proven improved survival
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15
Q

If child is under 3 is RT used?

A
  • usually delayed because of associated risks, but control rates are higher when radiation is used
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16
Q

What is the typical RT fields for CNS treatment?

A
  • 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
17
Q

What is the technique for the lateral skull fields?

A
  • 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
18
Q

What is the CNS brain technique with VMAT?

A
  • 1-2 arcs

- an extra arc using floor turn to achieve OAR may be needed

19
Q

What are the important OAR to consider in skull fields?

A
  • optic chiasm and nerves (54Gy), globes (45Gy)
  • cochlea (20-30Gy)
  • brainstem (54Gy)
  • hypothalamus and pituitary dose to be minimised
20
Q

What are some considerations for the lateral skull fields?

A
  • 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)
21
Q

What is the consideration with using extended SSD for spine field?

A
  • increased divergence of beam

- could result in only needing one junction point

22
Q

What is the point of moving junction and where are they located?

A
  • to decrease hot and cold spots (dose over junction is smooth transition)
  • each junction will have a set of at least three, 5mm junctions
23
Q

Why is there a gap on the skin between the two spinal fields?

A
  • so the hot spot or overlapping of beams occurs in the PTV and not on the skin
24
Q

What is the advantage of treating prone?

A
  • access to spine for palpation of set-up and field placement
  • skin marks for junction
  • general accuracy
25
Q

What is the advantage of supine?

A
  • more comfortable and feeling of security

- access to anaesthesia

26
Q

What is the positioning when patient is prone?

A
  • torso and legs elevated and support (styrofoam board and vacbag, bolster under ankles)
  • head supported with a comfortable face-rest (prone cushion, two-piece shell)
  • arms by sides with shoulder supported and drawn inf (minimise obsuring vertebrae on lateral fields)
  • c-spine horizontal (ensure no skin folds on neck)
  • chin not tucked too far (spine field not to diverge into mouth)
27
Q

What is the positioning when the patient is supine?

A
  • full body vac bag for support & reproducibility
  • head and shoulder mask
  • arms by side with shoulder supported and drawn inf (minimise obscuring vertebrae on lateral films)
  • c-spine as horizontal as possible
  • chin raised only to avoid exit from spine field
28
Q

What are the steps for treating prone on the linac?

A
  • set-up treatment prior to patient in room
  • position patient then straight and level and fit mask
  • set-up lateral skull fields
  • check and daily set junction
  • treat lateral fields as prescribed (IGRT)
  • back in room to position upper spine field
  • look at junctions
  • treat upper spine (IGRT)
  • back in room
  • position lower spine field
  • look at junctions
  • treat lower spine (IGRT)
29
Q

What are the side effects of CNS RT?

A
  • erythema, dry and most desquamation
  • oedema
  • hair loss (20-40Gy temporary, >40Gy may be permanent)
  • drowsiness & lethargy
  • decreased mental status/cognitive impairment
  • worsening of tumour symptoms
30
Q

What are the cognitive impairments caused by RT?

A
  • decreased IQ
  • decrease visual, spatial, motor, fine motor, memory and arithmetic skills
  • increases in child <7 yo*
31
Q

What is the patient care?

A
  • assess patient well being and emotional stability
  • encourage patient to eat well and rest
  • weekly blood test
32
Q

What are some consideration when assessing a paediatrics well being?

A
  • may need more time
  • prepare separate area to talk
  • patient can be aggressive
  • must consider parents needs as well

CSB092 (9 decks)

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