Small AVMs that are deep or in eloquent areas are often treated with radiosurgery instead of surgery. Radiosurgery uses a single high dose of radiation and has an obliteration rate of 70-80% at 2 years. Frame-based radiosurgery requires invasive head fixation for imaging and treatment, while frameless radiosurgery with the Cyberknife does not require an invasive frame. Preliminary studies show frameless radiosurgery has obliteration rates similar to frame-based radiosurgery but is better tolerated as an outpatient procedure without head frame fixation.

1.  Small AVMs need treatment with either surgery or radiosurgery
 Deep seated & eloquent area AVMs need radiosurgery treatment
 Radiosurgery is single fraction, usually dose more than 18 Gy to the nidus
 Obliteration rate (cure rate) is 70-80% at 2-year evaluation
 Gammaknife / Linac based systems: need invasive frame
 Cyberknife: No need for invasive frame
Out-patient procedure, excellent compliance
Obliteration rate is similar to frame based systems
Arteriovenous malformation

2. Radiosurgery experience in AVMs
Author (yr) Pt No FU (yr) Ave Dose
(Gy)
Obiteration
rate (%)
Complications
Flickinger et al
1987-1997
351 4.2 20 75 Necrosis,
neurological
deficits
French Dose
Response study
100 5 20 70
8 pts had
delayed
complications
Pollock et al 144 2 20 73 20 pts had
neurological
deficit
AVM<3 cm; SM Gr I-III
At 2 yr FU with DSA: Obliteration rate is 70-80%
Persistent Neurological deficit: <9%

3. 8 pts developed
radiation edema
Radiosurgery experience in AVMs from India
Only few prospective studies from India on AVM with SRS
Three studies showing at per obliteration rate & toxicity as western literature
SRS is feasible in our set up

4. Rigid frame based SRS: Work Flow
Fixation of frame
DSA
CT Scan
Image fusion
Planning
QA (LUTZ test)
Treatment
One day procedure
Need admission of patient
Frame fixed >6-8 hours

5. Jalali, Dutta et al. J Cancer Res Ther, 2009
Min Max Mean SD
Nidus Volume (cc) 1.1 5.6 3.6 1.6
Marginal dose (Gy) 14.4 25 19.2 3.2
12 Gy normal brain vol (cc) 3.3 15.3 8.3 4.2
Maximum dose (Gy) 16 27.5 22 3.7
12 Gy marginal volume (cc) 0.3 9.6 5 4.4
Isodose Coverage (%) 80 91 87.5 3.3
Optic Chiasm dose (Gy) 0.5 0.5 0.4 0.01
Brainstem dose (Gy) 0.5 6 2.5 2.5
(n=23)
Nidus Vol: 3.6 cc
Mean marginal dose: 19.2
(14.4-25 Gy)

6. Follow up (mo) Mean
24.3
(1.57 to 71.2)
Median 22
Number of patient referred for SRS 87
Number of patients planned for SRS 23
Number of patients treated with SRS 21
LFU status clinical examination No deficits 22
Neurological deficit persists after 2 yr FU 01
Type of Imaging done for Assessment
MRI and MRA done at 2 yrs FU 15
DSA 12
Imaging awaited on follow up 06
Last Follow up status on Imaging
MRA proven obliteration 15
Obliteration confirmed on DSA 11
No Obliteration on DSA 01
Complication after SRS
No complication 18
Temporary worsening 02
Persistent neurological deficit 01
Follow up & obliteration rate
Obliteration rate at 2 yr follow up DSA: 92%
Median FU: 22 mo
Obliteration rate: 92%
Persistent Deficit: 1 pt

7. Rigid frame (screw) based radiosurgery
Issues with frame fixation
Pain & hematoma
Fixed frame: 6-8 hours
One day procedure

8. Primary aim of the study:
 Evaluation of obliteration rate at 1 year
Secondary aim:
 Complication rate
 Evaluation of dose distribution parameters
 Evaluation of factors influencing obliteration rate
Title: Robotic -based stereotactic radiosurgery for selected AVMs:
preliminary experience from Apollo Hospital, Chennai
Study type: Prospective observational study (DNB dissertation)
Study duration: 3 years (Initial data presented here)
Pt number: 30 (Accrued till date)
Institute: Apollo Speciality Hospital, Chennai
Study design: Frameless Robotic SRS in AVM

9. Eligibility Criteria
 Radiologically confirmed AVMs in brain.
 Spetzler Martin grade I-III
 Nidus size <4 cm
 History of prior hemorrhage, headache, tinnitus or convulsion.
 Willing for robotic radiosurgery treatment
Ineligibility criteria
 Active haemorhage
 Large AVMs (>5 cm nidus)
 Presence of aneurysm or AV shunting
 Presence of calcification and intranidal fistula
 Previous radiation
(n=30)
Study design: Frameless Robotic SRS in AVM
Title: Robotic -based stereotactic radiosurgery for selected AVMs:
preliminary experience from Apollo Hospital, Chennai

10.  30 pts willing for Robotic SRS fulfilling the criteria accrued from Oct 2011 & have
more than 6 month FU were accrued for analysis
 Site distribution: 14 in temporo-parietal region, 10 in frontal, 4 had intraventricular ,
1 in thalamic and 1 in cerebellar region .
 Planning CT, CT angiogram, MRI, MR angiogram with 1 mm slice thickness.
 Fusion and planning with Multiplan, Accuray system
 Dose prescription was considered according to the flickenger’s model keeping
obliteration rate >80% & severe neurological toxicity <2%
 6Dskull tracking .
Study design: Frameless Robotic SRS in AVM
(n=30)

11. Frameless SRS: Work Flow
Thermoplastic mask
CT Angio
MR Angio
CT Scan
Image fusion
Planning
QA
2 days procedure
OUT PATIENT
No admission of patientTreatment with mask
Next day:
Day 1:

12. Planning: Frameless Robotic SRS in AVM
(n=30)

13. Treatment delivery: Frameless Robotic SRS in AVM
Treatment time: 20-45 min
Thermoplast based SRS
Pts received Dexa/ PPI
No acute toxicity for majority of patients (one pt had brain oedema requiring MDT)

14. Age (yr) mean (SD) 31.13 YRS
Range 6- 60 YRS
Gender male 17
Female 13
Duration of symptoms (mo) Mean 5.8
Range 1-60
Primary presenting symptoms
Headache alone 12 (40%)
Convulsions alone 6(20%)
Neurological deficit alone 3(10%)
Headache and neurodeficit 1(3%)
Headache and convulsion 8(27%)
Location TP region 14
Frontal 10
Intraventricular region 4
Thalamic 1
Cerebellar 1
Demographic profiles: Frameless Robotic SRS in AVM
AVM size <1cm 0
1-2 cm 2
2- 3 cm 18
3 - 4 cm 10
SM grade
I-II 18
III 12
Previous H’hge 12
Previous neurodeficit 3
(n=30)

15. Nidus Vol: 2.97 cc
Marginal dose:17.5 Gy (15-22 Gy)
Isodose prescription: 85%(80-90%)
Treatment time: 35 min (23-70 min
Dosimetric profile Min Max Mean
Nidus volume (cc) 0.46 7.7 2.97
Max dose (Gy) 15 22 17.5
Isodose coverage (% ) 80 90 85
Optic chiasm dose (cGy) 4 760 280
Rt eye dose (cGy) 3 448 146
Lt eye dose (cGy) 4 719 108
Beam lets 56 165 107
Treatment time (min) 23 70 35
HI 1.09 1.25 1.17
(n=30)
Dosimetric parameters: Frameless Robotic SRS in AVM

16. Follow up duration(in months)
Mean* 14
Median 6-30
Pt condition on last followup
Normal* 18
Deficits Nil
Type of imaging
MR angio at 6 months 30
MR angio at 12 months 16
MR Angio obliteration more than 1
yr follow up
Complete obliteration 13
Reduction in nidus volume 3
OUTCOME
MR ANGIO >1 YR - 16 pt
COMPLETE OBLITERATION - 13 pt (81%)
(n=30)
Results: Frameless Robotic SRS in AVM
Follow up: 14 months
Median Dose: 18 Gy
Obliteration rate: 81%
No Persistent Neurological deficit

17. Framebased versus Frameless SRS in AVM
Frame based
Frameless
Rigid Frame
Frame Fixed: 4-8 hrs
Pain/ Hematoma
Admission
Thermoplastic mask
Mask with pt: <30 min
No Pain/ Hematoma
Out-patient

18. Framebased versus Frameless SRS in AVM
Problems with Screws
Pain / Hematoma
Compliance issue
Long duration fixed frame (4-8 hrs)
‘Quality of life’ issue
Subdural hematoma 10%

19. Framebased versus Frameless SRS in AVM
Frame based
Frameless
Dosimetry & treatment parameters
Nidus Vol: 3.6 cc
Mean marginal dose: 19.2
(14.4-25 Gy)
Frame fixed 4-8 hrs
Nidus Vol: 2.97 cc
Marginal dose:17.5 Gy (15-22 Gy)
Isodose prescription: 85%(80-90%)
Treatment time: 35 min (23-70 min

20. Framebased versus Frameless SRS in AVM
Frame based
Frameless
N=23
Median FU: 22 mo
Median does: 19.2 Gy
Obliteration rate: 92%
Persistent Deficit: 1 pt
N=16
Median FU: 14 months
Median Dose: 18 Gy
Obliteration rate: 81%
No Persistent Neurological deficit
Obliteration rate & Toxicity

21. Frame based versus Frameless SRS in AVM
- It seems, Obliteration rate in both frame based & frameless
almost similar
- In frame based system, frame usually used for 4-8 hrs &
frameless system only 30-45 min
- Compliance higher with frameless, out-patient treatment
- ‘Early quality of life’ better with frameless
- In Multiplan planning system dosimetric parameters exciting

22. Flickinger et al.. Rad Onc 2002; 63:347-354.
Flickinger model
Dose prescription (Isocentre)
Marginal dose ( Gy)
12 Gy normal brain vol (cc)
Obliteration:
Depends upon marginal dose
Complication:
Depends upon 12 Gy normal brain vol

23. Beam reduction effect on 12 Gy Normal brain Vol
Optimum plan after approval taken for study
Marginal dose: 22 Gy; Pres Isodose: 85%
Coverage: 99.5%
Nidus size: 2.5 cm
Nidus Vol: 5.2 cc
12 Gy Normal Brain Vol: 22.5 cc
Beams: 85
Total MU:14414
Min MU: 15
Max MU: 622
Beam reduction done by reducing beams with minimum MU
in steps of 50, 100, 150, 200, 250 MU
Collimator size kept same
Prescription Isodose changes to keep Nidus coverage >99%

24. 85
79
59
51
33
26
0 50 100 150 200 250
Beam reduction effect on 12 Gy Normal brain Vol
No of Beams
Beam reduction in steps of 50 MU
Increasing the beamlets MU cutoff limit reduce low MU beams

25. 85 79 59 51 33 26 23 22 21 20
CI 1.67 1.67 1.85 1.78 3.12 3.54 3.75 3.96 3.83 3.7
nCI 1.69 1.69 1.86 1.79 3.14 3.57 3.77 3.99 3.87 3.73
HI 1.18 1.18 1.2 1.2 1.72 1.85 1.92 2 2 2
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
CI/nCI/HI
MU 14106 14190 14512 14189 16500 17523 17171 18558 17621 17299
Coverage (%) 99 99.1 99.3 99.1 99.2 99.2 99.3 99.2 99.2 99.1
Pres Isodose 85 85 83 83 58 54 52 50 50 50
12Gy Vol 23.5 26.4 27.5 25.8 36.6 39.9 44.6 45 45.4 46.8
Beam reduction effect on 12 Gy Normal brain Vol

26. 23.5
26.4 27.5
25.8
36.6
39.9
44.6 45 45.4 46.8
85 79 59 51 33 26 23 22 21 20
12Gy Normal brain Vol (cc)
85
79
59
51
33
26
0 50 100 150 200 250
No of Beams
85 79 59 51 33 26
Beam reduction effect
Beam reduction effect on 12 Gy Normal brain Vol
Beams
Correlation Coefficient: 95.6%
p-value: 0.003
Pearson correlation test

27. Beam reduction effect: Neurodeficit probability
0
5
10
15
20
25
30
35
40
85 79 59 51 45 33 26 22 21
Occipital
Frontal
Parital
PersistentNeurologicaldeficitprobability(%)
Beam numbers
20-50% increase in PND with beam reduction
According to Flickinger et al.. Rad Onc 2002; 63:347-354.

28. Nidus
Diameter
Coverage
(%)
Pres Isodose CI
2.5 cm 99 85 1.67
3.5 cm 99.4 77 1.35
4.5 cm 99.9 73 1.3
Effect of increased nidus vol on 12Gy Normal brain Vol
Nidus size: 2.5 cm
Nidus Vol: 5.2 cc
Marginal dose: 22 Gy
Coverage: 99.5%
Presription Isodose: 85%
0.5 cm margin to Nidus
Nidus diameter: 3.5 cm
1 cm margin to Nidus
Nidus diameter: 4.5 cm
Marginal dose: 22 Gy
Coverage >99%
Change Collimeter
Change prescription Isodose
Evaluate 12Gy Normal brain Vol
PTV2.5
PTV3.5
PTV4.5

29. Nidus
Diameter
Beams
Correlation
Coeff
p-value
12Gy Vol
(cc)
Correlation
Coeff
p-value
2.5 cm 85
99.6 0.003
23.5
93.4 0.0523.5 cm 167 63.6
4.5 cm 227 247
85
167
227
2.5 cm
Nidus
3.5 cm
Nidus
4.5 cm
Nidus
p-value: 0.003
23.5
63.6
247
2.5 cm
Nidus
4.5 cm
Nidus
p-value: 0.052
3.5 cm
Nidus
No of Beams 12Gy Normal Brain Vol (cc)
Impact of larger nidus

30.  Obliteration rate: It seems, Frameless SRS system is similar to frame based
systems
 Frameless system: Compliance is excellent, out-patient procedure
 Multiple beamlets may have dosimetric advantages with lesser 12 Gy
normal brain volume and acceptable marginal dose
 ‘Quality of life’ and acceptance by patient is excellent with frameless system
AVM- Conclusions