SRS and SRT Flashcards
What defines sterotactic?
- high precision
- small targets
- high dose
What does SRS allow?
- steep dose gradient and thus minial dose to OAR
- increased conforminty
How is conformity achieved?
- use of multiple non-coplanar beams
What is SRS?
- single high dose of radiation
What is SRT?
- treatment is delivered in more than one fraction
What are the indications for SRS/SRT?
- small tumour size
- tumour location
- pathology of tumour
- the patient
- tumour recurrance
What are the acute side effects of SRS?
- headache
- nausea/vomitting
- visual disturbances
- swelling
What are the late side effects of SRS?
- facial weakness
- numbness
- hearing loss
What are the advantages of stereo over VMAT?
- minimal damage to surrounding tissue
- treat to higher doses
- treatment can be given mutliple times
What are the most common sites for SRS?
- acoustic neuroma
- meningioma
- cranial mets
- AVM (arteriovenous malformation)
- GBM (glioblastoma multiforme)
What is acoustic neuroma?
- benign tumour of the 8th cranial nerve
What are the presentation symptoms or acoustic neuromas?
- hearing loss
- tinnitus
- balance disturbances
When is SRS used for acoustic neuromas?
- when surgery risks damage to facial nerves and hearing
- 12Gy in 1#
What is meningioma?
- benign tumour arsiing from meningeal tissue
When is SRS used for meningioma?
- inoperable or small tuours
- SRS: 18-20Gy in 1#
- SRT: 50-60Gy in 25-30#
When is SRS used for mets?
- can treat up to 5 in one session
- 16-20Gy in 1#
What is AVM?
- vascular abnormality
What are the presentation of AVM?
- intracranial bleed
- seizures
- problems with movement speech or vision
When is SRS used for AVM?
- where surgery or embolisation is high risk of failed
- 15-20Gy in 1#
What is a GBM?
- highly malignant and fast growing tumour
What are the presentations of GBM?
- headache
- nausea/vomitting
- seizures
- memory loss
- changes in speech or personality
- walking difficulties
When is SRS used for GBM?
- reccurence
- 6-16Gy in 1#
Why is MRI used?
- excellent definition of tumour volume
and critical structures
What occurs in sim for SRS patients?
- in treatment position lying on brainlab couch overlay
- cranial array positioned over patient to ensure head fits in
What are the advantages of brainlab mask?
- suitable for SRS and SRT
- non-invasive
- forehead, nose and mouth re-enforcement for extra stability
- re-usable
What are the dosimetric considerations for SRS?
- beam vs arc depends on tumout size and location
- numer of beams and floor angles dictates length of treatment and need to consider patient tolerance
- achieve most optimal plan
What are stero plans presribed to achieve?
- 80% iso line covering PTV
What are the patient pre-treatment preparations?
- obs taken
- nurse administer lorazepam
How does exactrac work once the patient is on bed?
- patient moved to iso defined from sim
- x-rays taken and infr-red detector moves patient bed position adjusted
- once in tolerance treatment starts
- imaging is repeated every time floor angle is changed
What are the imaging tolerances?
- > 3Gy: 0.5mm
- <3Gy: 0.9mm
- VMAT: 3mm
What do the patients do after SRS treatment?
- wheeled out in wheelchair
- obs repeated by nurses and monitored for 30 mins
- not to drive home
