Stereotactic Lecture

Question 1

What is Stereotactic Radiation?

Answer 1

Stereotactic- precise positioning in a three-dimensional space
Highly precise treatment
Small targets
High dose
Use of multiple non-coplanar beams or arcs
Steep dose gradient - minimial dose to critical structures and healthy tissue
Conformal

Question 2

What is SRS and SRT?

Answer 2

Stereotactic Radiosurgery - single high dose of radiation

Stereotactic Radiotherapy - Treatment is delivered in more than one fraction.

Question 3

What are indications for SRS/SRT?

Answer 3

Small tumour  size
Tumour location 
Pathology of the tumour 
The patient 
Tumour recurrence

Question 4

Side effects of SRS/SRT?

Answer 4

Acute: headache, nausea, vomiting, visual disturbances, swelling (usually managed with steroids)

Delayed: Facial weakness, numbness, hearing loss

Question 5

What are advantages of stereo over VMAT?

Answer 5

Minimal damage to surrounding tissue
Treat to higher doses
Treatment can be given multiple times

Question 6

What are clinical examples of brain lesions treated with SRS?

Answer 6

Acoustic neuroma - benign tumour of 8th cranial nerve. Presents as hearing loss, tinnitus. 12Gy in 1#.

Meningioma - usually benign tumour. SRS: 18 - 20Gy. SRT: 50 - 60Gy @ 1.8 -2Gy/ #.

Cranial Metastases - 16 -20Gy in 1# (per met). Can treat 5 mets per session (1.5hrs).

AVM - Arteriovenous Malformation - vascular abnormality. SRS: 15-20Gy in 1#

GBM - Glioblastoma Multiforme - highly malignant SRS: 6-16Gy /1#

Question 7

What are the procedure steps for stereotactic treatments?

Answer 7

1. MRI (used for all patients to delineate tumour and OAR volumes)
2. Simulation (Performed in treatment position with patient lying on Brainlab couch overlay. 3D printed cranial array positioned over patient to ensure head fits within it. CT - 1MM slices).
3. Planning (MRI and CT fused together. Contouring completed. Need to consider whether to use beams or arcs - depending on tumour size and location).
4. Quality Assurance
5. Treatment

Question 8

What is the BrainLab Elements multi-brain Mets SRS planning used for?

Answer 8

Used to plan multiple brain metastases. 
Can plan SRS and hypo-fractionated SRT.
Indications: 
  - Max 10 mets 
  - Max GTV diameter 3cm 
  - Max cumulative GTV volume of 30cc 
  - Dose to 80% isodose line 
  - Max dose = 125 -140% of prescribed dose