SRT Flashcards
Stereotactic definition
Precise positioning in a 3 Dimensional plane
Highly precise treatment
Small targets
High dose
Principles of Stereotactic
Use of multiple non-coplanar beams or
arcs
•Achieves a steep dose gradient -
minimal dose to critical structures and
surrounding healthy tissue
•Achieves conformity
SRS versus SRT
Radiosurgery (SRS)
- Single, high dose of radiation
•Radiotherapy (SRT)
- Treatment is delivered in more
than one fraction
Indications for SRT/SRS
•Small tumour size
•Tumour location
•Pathology of the tumour
•The patient
•Tumour recurrence
How does stereotactic work
Tumour reduction occurs at the rate of
normal growth for the specific tumour cell
Side effects
ACUTE: Headache, nausea,
vomiting, visual
disturbances, swelling
(usually managed with
steroids)
•DELAYED: Facial weakness,
numbness, hearing loss
Advantages of stereo over VMAT
Minimal damage to surrounding tissue
•Treat to higher doses
•Treatment can be given multiple times
What clinical sites are treated
Malignant or benign
Acoustic neuroma
Meningioma
Cranial Mets
GBM
Acoustic neuroma
Benign tumour of the 8th
cranial nerve
• Presentation: hearing loss, tinnitus & balance
disturbances
• SRS utilised when surgery risks damage to facial nerves and hearing • SRS12Gy/1#
Meningioma
Usually benign tumour
arising from meningeal
tissue
•Stereotactic for inoperable
or small tumours
•SRS: 18-20Gy
•SRT: 50-60Gy @ 1.8-2Gy/#
Brain Mets
Metastases in the
brain arise from a
variety of primary sites •Patients can present with 1 or many mets •Stereotactic dose of
16
-20Gy/1# per met
GBM
Highly malignant and fast growing – average survival time 12 months •Symptoms of gliomas may include headaches, nausea, vomiting, seizures, memory loss, changes in speech or personality and walking difficulties •Stereotactic used at time of
recurrence
•SRS: 6
-16Gy/1#
Planning to treatment workflow
MRI
CT Sim
Planning
QA
Treatment
Why MRI
•Essential for all patients
•Provide excellent definition of tumour volume
and critical structures
•Request scans that will best show the target
volume
Stereo mask
Mask made in 20 min
Ensure eyebrows, nose, forehead, cheeks visible
Laterally outer canthus to anterior of Tragus
Two parts - 1 under patients head and one over
CT parameters
CT – 1mm slices
•Primary image set for planning
Planning
• Importing of image data sets (MRI + CT)
• Fusion of data sets
• Contouring
• Dosimetry
• RO approval
• Export to treatment
Image fusion
CT and MRI images are fused together
•CT is always the primary image
•Fusions are automatic, but must be
checked
Hyperarc planning
Select your treatment targets
•Assign prescribed dose to each target – can have different doses in the same plan
•Isocentre positioned in the middle of single PTV or middle of multiple PTVs
•Set floor and gantry angles
•Floor - 0, 45, 315, 270
•Gantry 360deg or 180deg arcs
•Optimise collimator position
•Enter planning goals into optimiser for PTVs and OARs
•Avoid entry and exit on OARs or previously treated PTVs
Visualise beam/arc to ensure they’re not treating OARs or other PTVs
Reduces collision risks
Dose export
Once the plan has been approved by the RO it is
exported into:
o MOSAIQ - the R&V system
o ExacTrac - the BrainLAB isocentre positioning
system – Buderim patients
Patient pre-treatment prep
Single shot patients
• Observations taken
• Nurses tend to administer
Ativan (Lorazepam)
Dexamethasone
Treatment times
20 - 90 mins
What are primary sites for Mets
Kidney
Lung
Melanoma
Breast
Colorectal
Symptoms of brain cancer
Headaches, seizures, dizziness, memory gait, verbal issue, confusion
