1. LEKSELL GAMMA KNIFE PERFEXION
THE STATE-OF-THE-ART RADIOSURGEY TOOL
Josef Novotný jr.
UPMC Cancer Centre, Pittsburgh, USA
Josef Novotný,
Medical Physics Department
Na Homolce Hospital, Prague,
Czech Republic

2. Pioneering radiosurgery 1951 - 1968
The first prototype of the Leksell Gamma Knife was installed in 1968 at Sophiahemmet Hospital in Stockholm, Sweden.

3. Gamma Knife model U
UPMC GAMMA KNIFE MODEL U • Installed in • 201 sources with 4, 8, 14 and 18 mm collimators • Manual setting of coordinates

4. Gamma Knife model B
Manual setting of coordinates
Trunnion fixation

5. Leksell Gamma Knife - principles
Model B, C, 4C

6. Gamma Knife model C
Installed in • 201 sources with 4, 8, 14 and 18 mm collimators • Automatic Positioning System [APS]

7. Gamma Knife model 4C Last treatment on 12.11.2009
No of treated patients
Installed in • 201 sources with 4, 8, 14 and 18 mm collimators • Automatic Positioning System [APS] * More safety features

9. Development of the PERFEXION
In 2002 formed a group within Leksell Gamma Knife Society consisting of neurosurgeons, radiation oncologists and medical physicists.
ELEKTA asked this group the simple yet complex question:
What is the ultimate tool for Gamma Knife surgery?

10. Identified Seven Critical Features for the new system
Best dosimetry performance (accuracy, precision, reliability)
Best radiation protection for patients and staff
Unlimited cranial reach
Full automatization (with the maximum of commercial parts)
Outstanding patient and staff comfort
Keeping the unique robustness of the Gamma Knife
Consistency with previous Gamma Knife systems

11. PERFEXION DESIGN
FEATURES

12. Leksell Gamma Knife PERFEXION Introduced in 2006
New collimator design
New safety doors and shielding
Patient positioning system

13. Automatic Positioning System (APS) versus Patient Positioning System (PPS)Z X 13

14. Automatic Positioning System (APS) versus Patient Positioning System (PPS)Z X

15. Advantages of the Patient Positioning System
Very easy and fast to operate  no positioning checks needed
Time efficient for the patient treatment  all targets can be treated mostly in a single run
High patient comfort  whole patient’s body moves in a treatment position

16. LGK PERFEXION radiation unit and collimator
sector design

17. Collimator System for LGK PERFEXION
4, 8, 16 mm collimators
No collimator helmets
192 Co-60 sources
Cylindrical source geometry

18. Treatable volume - Focus access
Leksell Gamma
Knife B, C, 4C
Leksell Gamma
Knife PERFEXION
- Increased treatable volume by more than 300%
- Cerebral cases
~ 10% increase in available number of patients for existing indications due to extended reachability
- Head & neck
~ 10 % additional patients from lesions in paranasal sinuses, orbits and some upper cervical lesions
- Cervical lesions
~ 20% additional with upcoming fixation technique

19. PERFEXION CALIBRATION

20. Calibration Procedure
Calibration of source positions, i.e. calibrating the sector positions
Calibrating the movements of the Patient Positioning System.
Calibrating the Patient Positioning System vs. the Radiological Focus

21. Calibration and QA Procedures for PPS
1) Service Diode Test Tool
2) On-site Diode Test Tool
3) LEICA Laser Tracking Tool 3 1 2 1
3 - Long Diode X=160, Y=100, Z=22
1 - Central Diode X=100, Y=100, Z=100
2 - Short Diode X=100, Y=50, Z=115
4) Focus Pin Prick Film Test

22. Results – PPS Daily QA with On-site Diode Test Tool
RADIAL = 0.1 ± 0.1 mm

23. Results – PPS QA with Service Diode Test Tool
Central diode RADIAL = ± mm
Short diode RADIAL = ± mm
Long diode RADIAL = ± mm

24. Calibration Procedure
Calibrating the movements of the Patient Positioning System. Weight dependence.

25. How does weight effect results?

26. Results – PPS QA with Service Diode Test Tool

27. Patient and Staff Radiation Protection

28. Extracranial doses measurement
Alderson Rando Phantom with LiF-100 TLD chips

29. Extracranial doses for single isocenter

30. Extracranial doses for single isocenter

31. Extracranial doses for different systems

32. Radiation protection in the treatment room1 2 3 4 5 6 A B C D E F G H
100cm
90cm
Measurements performed:
1] Sources and doors closed
2] Sources in shielded position, doors open, patient in a treatment position
3] Sources opened, patient in a treatment position, doors open

33. Radiation protection in the treatment room
Beam ON, door open [ mSv/h]

34. Radiation protection in the treatment room
Beam ON, door open
Beam OFF, door closed
[ mSv/h]

35. PERFEXION Treatment Planning

36. Treatment Planning Leksell GammaPlan® PFX™
We want  Maximum dose to the target
 Minimum dose to the surrounding healthy tissue
 Optimized dose distribution
We can use  Multiple beams
 Different weighting (time)
 Multiple iso-centers
 Different collimators
 Plugs

37. 4 months post Gamma Knife® surgery
Treatment Planning
Leksell GammaPlan® PFX™
A] Patient data - personnel data
- head data
4 months post Gamma Knife® surgery
B] Beam data – dose distribution
- PDD
- linear attenuation coefficient
- dose rate
- output factors
C] Images – MR, CT, PET, angiography
D] Calculation algorithm

38. Treatment Planning Leksell GammaPlan® PFX™ * Dose performance
Collimator design provides almost unlimited ability for sculpturing the dose distribution
* Shot features enabled
Classic (combination of 4, 8, 16 mm shots)
Composite (any combination of B, 4, 8, 16 mm sectors)
Dynamic shaping
Collimator system
* PC based treatment planning system with client-server architecture
AAPM training course , Prague 2008

39. Treatment Planning Dose calculation algorithm Dose (x,y,z) = Geometry
Inverse Square Law
Output Factors
Correction for Source Decay
Dose (x,y,z) = Geometry
 Physical Factor
 Calibration
 Time
Position
Dose Profiles
Initial Source Strength
Attenuation
AAPM training course , Prague 2008

40. Unlimited intracranial treatment reach
Leksell GammaPlan® PFX™

41. Unlimited intracranial treatment reach
Leksell GammaPlan® PFX™
Dose Plan for
Jugular Schwannoma

42. Composite shots
Leksell GammaPlan® PFX™

43. Dynamic shaping
Leksell GammaPlan® PFX™

44. Comparison of Dosimetric Characteristics PERFEXION versus 4C dosimetry

46. Dosimetric Comparison

47. Results – X, Y, Z profiles

48. Results – Cumulative DVH
8 mm
4 mm
Matrix grid size 0.5 mm

49. Comparison of efficiency and dose planning
PERFEXION versus 4C

51. Efficiency Lindquist et al. Regis et al. Niranjan et al.
PERFEXION versus 4C
Lindquist et al.
 Median saved time 12 min
 Significant increase in beam-on-time
on PFX (median 46 min)
5 patients with complex benign tumors
Regis et al.
 Median saved time 20 min (p<0.01)
 No significant difference in beam-on-time
Randomized study
Total 100 patients on 4C (80% benign tumors)
Total 100 patients on PFX (75% benign tumors)
Niranjan et al.
Benign tumors
Multiple metastases
Median saved time 16 min (p<0.01)
No significant difference in beam-on-time
Median saved time 53 min (p<0.01)
16 patients with benign tumors
21 patients with multiple metastases (total 117 tumors)

52. Treatment of multiple metastases
Leksell Gamma Knife PERFEXION
Niranjan et al.2009

53. Treatment planning parameters-Optimization
Conformity index
Macroscopic target volume, GTV (gross tumour volume)
CI = (PTViso/PTV)
Microscopic distribution-rim
Paddick’s Conformity index
Planning target volume ( PTV)
PCI = (PTViso )2 / PIV*PTV
Dose gradient index
Planning isodose volume PIViso
GI = (PIViso/2 )/ (PIViso)

54. Conformity Lindquist et al. 0.82 0.86 1.14 1.09 2.74 Regis et al. -
PERFEXION versus 4C
PCI
4C PFX CI
4C PFX GI
4C PFX
Lindquist et al.
0.82
0.86
1.14
1.09
2.74
Regis et al. -
Niranjan et al.
Benign tumors
Multiple metastases
0.60
0.81
0.51
1.08
1.63
1.11
1.85
2.78
2.91
2.67
3.12

56. Relocable frame – new challenge

57. Conclusions
The new Leksell Gamma Knife Perfexion provides unlimited cranial reach and significantly improves workflow, patient and staff comfort.
The system offers more dosimetry options for treatment planning including mainly composite shots. At the same time very good dosimetry consistency for 4 mm and 8 mm collimators exists with previous gamma knife systems.

58. Conclusions
Radiation protection for patients and staff is significantly improved compare to previous gamma knife systems. Extracranial patient doses are much lower compared to other competing technologies.
Excellent long term stability of the system was observed during our almost 2 years experience in Pittsburgh. No major technical issues occurred. There was zero down time during this period of time.

60. THANK YOU FOR YOUR ATTENTION