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

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

Gamma Knife model U UPMC GAMMA KNIFE MODEL U • Installed in 1987 • 201 sources with 4, 8, 14 and 18 mm collimators • Manual setting of coordinates

Gamma Knife model B Manual setting of coordinates Trunnion fixation

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

Gamma Knife model C Installed in 1999 • 201 sources with 4, 8, 14 and 18 mm collimators • Automatic Positioning System [APS]

Gamma Knife model 4C Last treatment on 12.11.2009 No of treated patients 10 525 Installed in 2006 • 201 sources with 4, 8, 14 and 18 mm collimators • Automatic Positioning System [APS] * More safety features

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?

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

PERFEXION DESIGN FEATURES

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

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

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

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

LGK PERFEXION radiation unit and collimator sector design

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

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

PERFEXION CALIBRATION

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

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

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

Results – PPS QA with Service Diode Test Tool Central diode RADIAL = 0.067 ± 0.036 mm Short diode RADIAL = 0.095 ± 0.033 mm Long diode RADIAL = 0.063 ± 0.025 mm

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

How does weight effect results?

Results – PPS QA with Service Diode Test Tool

Patient and Staff Radiation Protection

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

Extracranial doses for single isocenter

Extracranial doses for single isocenter

Extracranial doses for different systems

Radiation protection in the treatment room 1 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

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

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

PERFEXION Treatment Planning

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

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

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 8-16-8-16-8-16-8-16 * PC based treatment planning system with client-server architecture AAPM training course , Prague 2008

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

Unlimited intracranial treatment reach Leksell GammaPlan® PFX™

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

Composite shots Leksell GammaPlan® PFX™

Dynamic shaping Leksell GammaPlan® PFX™

Comparison of Dosimetric Characteristics PERFEXION versus 4C dosimetry

Dosimetric Comparison

Results – X, Y, Z profiles

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

Comparison of efficiency and dose planning PERFEXION versus 4C

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)

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

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)

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

Relocable frame – new challenge

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.

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.

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