Radiosurgery by Leksell gamma knife Josef Novotny, Na Homolce Hospital, Prague
Radiosurgery - Definition Professor Lars Leksell The tools used by the surgeon must be adapted to the task and where the human brain is concerned they cannot be too refined.
Learning objectives * to learn basic principles of Leksell gamma knife (LGK) radiosurgery * to discuss imaging, treatment planning and optimisation procedures * to discuss quality assurance for LGK treatments * to present examples of diagnoses treated by LGK
Radiosurgery - Definition Radiation dose High Gamma Knife surgery Stereotactic Radiation Therapy The delivery of a single, high dose of irradiation to a small and critically located intracranial volume through the intact skull Image Guided Radiation Therapy Low Smaller Intensity Modulated Radiation Therapy Conformal Radiation Therapy Target volume Conventional Radiation Therapy Larger
Radiosurgery - Definition Radiation energy is focused into a small volume of soft tissue. This volume must be well defined regarding localization, size and shape. The energy is delivered in one single session Therefore the radiation energy must be delivered selectively to the volume and the radiosurgical procedure must be reproducible.
Radiosurgery - Definition Conformity describes how well the prescription dose is fitted to the target volume High conformity, low selectivity Selectivity also takes irradiation to normal tissue into account High conformity, high selectivity
Radiosurgery Components of selectivity A number of components are directly or indirectly important for high selectivity: Beam penumbra Radiation source size Intra-collimator leakage Inter-collimator leakage Beam size Dosimetrical uncertainties Mechanical stability Treatment planning system Number of radiation fields
Radiosurgery Fundamentals of radiosurgery For each radiosurgery technique, suitable targets are limited to certain sizes and shapes for which an adequate selectivity level can be achieved. This means that indications suitable for a certain technology are limited by the selectivity level needed for a clinically effective and safe treatment. This selectivity level will in practice be constantly re-defined according to the most sophisticated science and technology.
Leksell Gamma Knife - principles Leksell gamma knife model B, C and 4C Radiation source: gamma rays from 60 Co No. of sources: 201 Collimators: 4, 8, 14, 18, mm 100 Re lative dos e [%] 90 80 70 60 50 40 30 20 10 0 1 Co - 60 X 4 MV X 6 MV 0 2 4 6 8 10 12 14 16 18 20 De pth in wate r [cm]
Leksell Gamma Knife - principles Protective shielding Spherical collimator helmet Leksell Stereotactic System Isocenter/ Target in the brain Automatic Positioning System Radiation source Co-60
Leksell Gamma Knife - principles Collimator helmet Source Shielding plug Final collimators
Leksell Gamma Knife - principles Re lative dos e [%] 100 90 80 70 60 50 40 30 20 10 Collimator 18 mm Collimator 14 mm Collimator 8 mm Collimator 4 mm 0 60 70 80 90 100 110 120 130 140 Coordinate X [mm]
Leksell Gamma Knife - principles 4 100.00 8 14 The beam size effect 80.00 18 80 % Helmet Penumbra % of central value 60.00 40.00 20.00 20 % 4 mm 2.8 mm 8 mm 5.0 mm 14 mm 8.1 mm 18 mm 10.1 mm 0.00 0.00 10.00 20.00 30.00 40.00 Off axis distance [cm]
Model U Leksell Gamma Knife - principles
Model B, C, 4C Leksell Gamma Knife - principles
Leksell Gamma Knife - principles Leksell gamma knife model C
Leksell Gamma Knife - principles Leksell gamma knife model 4 C
Leksell Gamma Knife - principles Leksell gamma knife model Perfexion Development 2000-2005 192 source 3 collimators Fully automatic First installation 2006 France 5/ 2008 about 25 installations
Leksell Gamma Knife - principles Leksell Gamma Knife C 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
Leksell Gamma Knife - principles Saving time: 1 hour / patient compared with Leksell Gamma Knife U/B 30 minutes / patient compared with Leksell Gamma Knife C/4C A real case study showed 4 hours for a 10 metastatic lesions patient Automation and workflow save 3-5 working weeks of physician time per year for a site with 200 patients per year Complete procedure implemented via one push button operation
Medieval radiosurgery and radiotherapy
Stereotactic target localization Step No 1 Step No 2 Frame fixation Indicator box
Stereotactic target localization MR indicator box CT indicator box DSA indicator box
Image definition Stereotactic target localization Space definition Axial Images Coronal images.....
Radiosurgery Imaging Leksell coordinate frame provides optimal stereotactic localization Supports all imaging modalities (CT, MRI, PET and Angio) Digital image transfer to Leksell GammaPlan
Treatment Planning We want Maximum dose to the target Minimum dose to the surrounding healthy tissue We can use Multiple beams Different weighting (time) Multiple iso-centers Different collimators Plugs
Treatment Planning A] Patient data - personnel data - head data B] Beam data dose distribution - PDD - linear attenuation coefficient - dose rate Re lative dos e [%] 100 90 Collimator 18 mm 80 Collimator 14 mm Collimator 8 mm 70 Collimator 4 mm 60 50 40 30 20 10 0 60 70 80 90 100 110 120 130 140 Coordinate X [mm] C] Images MR, CT, PET, angiography D] Calculation algorithm
Treatment Planning Leksell gamma knife Leksell GammaPlan 4 mm 8 mm 14 mm 18 mm 4 mm 3D gel dosimetry shape of individual shots from different collimator
Treatment Planning TV = Tumor Volume PIV = Prescription Isodose Volume
Treatment Planning Dose calculation algorithm Inverse Square Law Output Factors Correction for Source Decay Dose (x,y,z) = Geometry Physical Factor Calibration Time Position Dose Profiles Attenuation Initial Source Strength D( x, y, z) = z z s s f f z 2 e µ z OAR( z, r) D& cal, k 201 Time
Treatment Planning Parameters for optimisation Conformity index CI = (PTV iso )/(PTV) Conformity number CN = (PTV iso ) 2 / (PIV*PTV) Dose gradient index GI = (PIV iso/2 )/ (PIV) PTV iso target volume irradiated by planning isodose PTV planning target volume PTV iso/2 volume of half of the planning isodose PIV volume of planning isodose
Treatment Planning Parameters for optimisation PTV iso excellent acceptable unacceptable CI 0.95 0.9-0.95 < 0.9 CN 0.6 0.5-0.6 < 0.5 GI 3 3.0-3.2 >3.2 PIV PTV iso/2 PTV
Treatment Planning Leksell GammaPlan PFX * Dose performance Collimator design provides almost unlimited ability for sculpturing the dose distribution * Shot features enabled Classic Composite Dynamic shaping Collimator system 8-16-8-16-8-16-8-16 * PC based treatment planning system with client-server architecture
Leksell gamma knife 4C treatment with APS LGK Treatment
LGK Treatment Automatic treatment, supervised by redundant safety and verification systems Patient and doctor communicate via audio visual system
Quality control process tree
Quality control - LGK APS precision test Absorbed dose measurement Dose distribution and isocenter test
Quality control-distortion of scanners 3D VIEW CORONAL INSERT 3D INSERT AXIAL INSERT
Quality control-distortion of scanners 3D MRI X-ray angiogaphy CT image
Quality control-3d phantom measurements Head phantom LGP reconstruction Gel dosemeter
Physical and technical parameters Leksell gamma knife model B - 4C Isocenter accuracy: ± 0.5 mm Stereotactic target localization accuracy: ± 0.8 mm Stereotactic target irradiation accuracy: ± 0.2 mm Overall accuracy: ± 1.0 mm Absorbed dose accuracy : + 1,5 %
Clinical applications No of treated patients 1991-2005 world wide 207 units out 237 have reported per December 2005 6/2008 257 units Malignant tumors 42% Benign tumors 35% Vascular disorders 16% Functional diseases 7%
Clinical applications Na Homolce Hospital 2004-2006 Diagnosis 2004-2006 Benign tumors 39% Malignant tumors 29% 10% Vascular disorders 9% Ocular disorders 13% Total No of patients 2456 Functional disorders
Clinical applications Vascular diseases AVM AOVM Other vascular Benign tumors Acoustic neuroma Meningioma Pituitary adenoma Other benign tumors treatment 3 years 5 years 10 years
Clinical applications Malignant tumors Metastasis Glial tumors Other malignant tumors Treatment 6 years
Clinical applications Functional disorders Trigeminal neuralgia Intractable pain Parkinson s disease Epilepsy Other functional disorders Ophthalmologic indications Trigeminal neuralgia Uveal melanoma Other ophthalmologic indications Uveal melanoma
Clinical applications Glaucoma Four 8 mm isocenters
Radiosurgery using gamma knife An unbroken digital link 4 Efficiency 4 Convenience 4 Check-and-verify 4 Documentation 4 Data integrity 4 Speed