Week 11 - Stereotactic

Question 1

stereotactic RT

Answer 1

• highly precise treatment
• small targets
• high doses

Question 2

treatment principles

Answer 2

• use of multiple non-coplanar beams or arcs
• achieves a steep dose gradient
  
  • minimal dose to critical structures and surrounding healthy tissue
• achieves conformity

Question 3

SRS

Answer 3

radiosurgery
- single, high dose of radiation

Question 4

SRT

Answer 4

stereotactic radiotherapy
- treatment is delivered in more than one fraction

Question 5

indications for SRS/SRT

Answer 5

• small tumour size
• tumour location
• pathology of tumour
• the patient
• tumour recurrence

Question 6

advantages of stereo over VMAT

Answer 6

• minimal damage to surrounding tissue
• treat to higher doses
• treatment can be given multiple times

Question 7

cranial tumour sites

Answer 7

• acoustic neuroma
• meningioma
• cranial metastases
• GBM (glioblastoma multiforme)

Question 8

acoustic neuroma + presentation + treatment

Answer 8

• benign tumour of the 8th cranial nerve

presentation: hearing loss, tinnitus, balance disturbances

treatment: SRS utilised when surgery risks damage to facial nerves and hearing
- SRS 12.5Gy in 1#

Question 9

meningioma + treatment (SRS and SRT)

Answer 9

• usually benign tumour arising from meningeal tissue

stereotactic for inoperable or small tumours
- SRS 18-20Gy
- SRT 50-60Gy @ 1.8-2Gy per #

Question 10

brain metastases + treatment dose

Answer 10

• metastases in the brain arise from a variety of primary sites
• patients can present with 1 or many mets

stereotactic dose of 16-20Gy in 1# per met

Question 11

GBM + symptoms + treatment

Answer 11

• highly malignant and fast growing - average survival time 12 months

symptoms: headaches, nausea, seizures, memory loss, changes in speech or personality and walking difficulties

stereotactic used at time of recurrence
- SRS 6-16Gy in 1#

Question 12

MRI in SRS/SRT

Answer 12

• essential for all patients
• provide excellent definition of tumour volume and critical structures

Question 13

CT slice thickness

Answer 13

1mm slices for SRT/SRS

Question 14

image fusion

Answer 14

• CT and MRI images are fused together
• CT is always the primary image
• fusions are automatic, but must be checked

Question 15

dose prescription and aims for SRS/SRT

Answer 15

• stereotactic plans are usually prescribed so that the 80% isodose line covers the PTV
• aiming for 99% of the PTV to be covered with the prescribed dose

Question 16

imaging tolerance

Answer 16

> 3Gy/# tol is <0.5mm
<3Gy/# tol is <0.9mm
VMAT brain tol is 3mm

Question 17

acute side effects

Answer 17

headaches, nausea, vomitting, visual disturbances, swelling (usually managed with steroids)

Question 18

delayed side effects

Answer 18

facial weakness, numbness, hearing loss