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STEREOTACTIC TREATMENTDEFINITIONS AND LITERATURE

OVERVIEW

Doracy P. Fontenla, Ph.D.Associate Professor_AECOM

Associate Chief PhysicistNSUH-LIJ Health Systems

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Radiosurgery Definitions

Stereotactic/ Stereotaxy : Clinical procedurebased on reference markers to precisely locatea target within 3D-boundaries.

Combine the use of a stereotatic apparatus &radiation beams

Two modalities:Stereotactic Radiosurgery - SRS

orStereotactic Radiotherapy - SRT

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STEREOTACTIC RADIOSURGERY (SRS)

A “non-invasive” techniqueDelivers of a single high dose of radiationLimited, well-defined small intracranial target

volumesAvoids nearby normal tissue and critical structuresMinimize the dose to the adjacent brain tissue

STEREOTACTIC RADIOTHERAPY (SRT)

Employs same stereotactic techniques used for SRSRefers to delivering collimated beams of radiationin multiple fractions, to a stereotactically locatedtarget.

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SRS-SRT

Two way process:• Accurate shape definition and location of

lesion and adjacent neuro-anatomy, fromMRI, CT,CTA, Radiografic films, usingstereotatic frame.

• Accurately delivery of a very conformal plan.

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• SRS first developed by Leksell (late 1940’s)using orthovoltage X-Rays.

• Employed Heavy charged particles fromcyclotrons.

• Gamma rays Gamma Knife (201 60Co sources)• Megavoltage X-rays from linacs (4 to 18 MV)• First 3D treatment :Megavoltage unit, April

1948 (Kerst,1975)• First combined used of X-ray unit & stereotatic

frame: Leksel, 1950

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• High Doses (16 Gy to 22 Gy, generallyprescribed to the 80% or 90%)

• Delivered in 1 fraction

• Mandate very rigorous, thorough andmethodical QA.

• Written detailed procedures is mandatory.

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Achievable uncertanties in SRS(*)

3.7 mm2.4 mmStd. Dev. of Pos.Uncertainty

0.3 mm0.3 mmAngio (Pt.identification)

1 mm1.0 mmTissue Motion

3.2 mm1.7 mmCT Imageresolution

1 mm1 mmIsocenterAlignment

1 mm1 mmStereotaticFrame

(*) AAPM Report No 54:Stereotatic Radiosurgery

CT slice Thickness 1mm 3mm

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Linac Based (Xknife/Brainlab)

VS Radioactive Source (Co) Gamma Knife

•Collimator sizes:4 to 45 mm in 2.5 mm steps•Conformal SRS: withjaws/circles or MMLC; IMRT.• Extra-cranial: head andneck; body localization:spine, prostate, lung, liver•Tx Room can be used forother Tx modalities.

•Collimator sizes: 4,8,14,18 mm•Conformality is onlyattained through multipleisocenters•No extra-cranial targetspossible

•Requires dedicated Tx.Room.

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Gamma Knife

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Stereotactic Radiosurgery -Linac Based• A “non-invasive “

technique to delivera single high dose ofradiation, to limited,well-defined targetvolumes, whileavoiding nearbynormal tissue andcritical structures.

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Components of a Radiosurgery System

•Immobilization and Localization Instrumentation–Cranial–Head and Neck–Spine and Body

•Treatment Planning Software–Arcs, Conformal, IMRT, Frameless modules–Image Fusion™ software

•Linac and QA instrumentationCollimation System (MMLC, MLC, circular

collimators, and circular collimators with linacjaws)

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Stereotactic Hardware(Brain Lab)

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• Quick and easy mounting using a dedicated storage trolley

• Gantry at 180° position

• Immediate electronic and power connection

• Full communication and safetyinterlocks with Varian, Elekta andSiemens Linacs for IMRT anddynamic conformal arc treatment

m3 Linac Attachment

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• C-Series Clinacs• Conformal Beam• Dynamic Conformal Arc• Sliding windows or Step &

Shoot IMRT

m3 Linac Compatibility

• Oncor, Primus and Mevatron• Conformal Beam• Dynamic Conformal Arc• Automated Step & Shoot

IMRT

SL-Series• Conformal Beam• Conformal Arc

Trilogy & C- Series Clinacs

ELEKTA

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Elekta

Linac Compatibility

•Siemens:Oncor, Primus& Mevatron

•Varian (Trilogy & C-Series)•TomoTherapy

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Radiosurgery

ExacTrac® X-Ray 6D

m3®

mMLC

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CHARACTERISTICS OF STEREOTATIC(SRS) and (SRT)

• STEREOTACTIC COORDINATE SYSTEM(CRW, BRW) (CT, MRI, Angiography) (Linac)

allows accurate dose delivery to the target

• SHARP DOSE GRADIENTS AT FIELD EDGES :( Dose falls of to 50% of target dose within 3 - 4 mm)

• HIGHLY CONCENTRATED RADIATION DOSE :multiple non-coplanar arcs converging at theisocenter.

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SRS/SRT General Procedure• Diagnostic MR images of patient• Target/Organs contouring• Pre-plan using MR images (whenever

allowed by Tx plan software)• Placement of Head Ring• Stereotactic CT/Angio images• Transfer images to Tx Plan workstation• Fuse MR to CT images (optional)• Treatment Planning• QA of LINAC (previous to Tx.)• Verify correctness of Pt. Position• Treat patient

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m3 Treatment

PatientTreatment Completed

Patient fixation Imaging

Planning

Set-Up

15 min.

30 min.

10 min.

30 min.15 min.

Start

RadiosurgeryClinical Procedure

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Cancer Management

Diagnosis RadiationTherapy Chemotherapy

60% of cancerpatients undergo

surgery

50% of cancerpatients undergoradiation therapy

30% of cancerpatients undergo

chemotherapy

Surgery

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Rationale for StereotacticRadiotherapy

• Reduces risk of healthy brain and cranialnerve damage

• Allows for treatment in/or near critical areas(e.g., retina, brain stem, chiasm)

• Allows for safe treatment of larger lesions(> 3-5 cm.)

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Role of Radiosurgeryin the Management of Intracranial

Tumors• Potentially curative therapy in benign, non-invasive

tumors (pituitary adenomas, acoustic neuroma,meningioma, pilocytic astrocytoma).

• Adjuvant Therapy (Boost) for Benign or MalignantTumors (metastasis, glioma, medulloblastoma,ependymoma) .

• Preoperative Therapy for Vascular Tumors• Salvage Therapy for previously irradiated recurrent

tumors.

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INDICATIONS FOR STEREOTACTICSRS/SRT

• Acoustic Tumors (Schwannomas, Neuromas,Neurinomas, Nerve sheath tumors, Neurilemomas)

• Arteriovenous Malformations• Arteriovenous Malformations• Arterial Aneurysms• Craniopharyngiomas• Ependymomas• Glomus Jugulare Tumors• Hemangioblastoma• Medulloblastomas (Boost)• Meningiomas

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INDICATIONS FOR STEREOTACTICSRS/SRT

• Metastases• Optic Gliomas• Pinealomas• Pituitary Adenomas• Primary Brain Tumors (Glioblastomas,

Astrocytomas,CNS Sarcoma, CNS Lymphoma)• Retinoblastomas• Venous Angiomas• Functional Radiosurgery• Clinical studies for use in Parkinson’s and Epilepsy

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Typical Indications for Radiosurgery

Images courtesy of:1) UCLA, 2) Universitätsklinikum Charité Berlin, 3) Helios Klinikum Erfurt, 4) University of Rochester

Pre-SRS / 36 mth follow-up

AVM1 Brain Metastasis1 High GradeGlioma2 Meningioma3Low Grade Glioma1 Multiple Lung

Metastasis4

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Radiosurgery - MetastasisPre-Radiosurgery Post-Radiosurgery

6 months

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Radiosurgery AVMPre-Radiosurgery

6months

Post-Radiosurgery

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Clinical Indications for SRS / SRT

50%25%

15% 9% 1%

Malignant Tumors, 50% - Metastatic tumors, primary andrecurrent gliomasBenign Tumors, 25% - Meningiomas, acoustic neuromas, pituitaryadenomas, craniopharyngiomasVascular Disease, 15% - AVMs, cavernous angiomasPediatric Tumors, 9% - RetinoblastomasFunctional Disease, 1%

1997 Study. Courtesy Jay Loeffler, M.D., Harvard Medical School, Boston, MA

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Stereotactic Radiotherapy

• A hybrid technique thatcombines the benefits ofconventionalradiotherapy with thebenefits of stereotaxy.

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PHYSICAL COMPONENTS REQUIREDFOR SRS/SRT

1. Laser-Angiographic Target Localizer (LATL)2. BRW (CRW) CT /MR Localizer Frame3. Relocatable Head Frame (GTC)4. Patient Positioning Devices:

• Rectilinear Phantom Pointer (RLPP)• Laser Target Localizer Frame (LTLF)• Linac Couch Mount Adapter (LCMA)

5. Depth Confirmation Helmet (QA)

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SRS

SRT (GTC)(Gill-Thomas-Cosman)relocatble head frame

Placement of Head Ring

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Stereotactic Patient Set-upCT Localizer

• For CT / X-Ray localization

• Links Angio Images to CT

• Creates stereotactic coordinatesystem

• Large scan range (185 mm)

• No fixation to CT couch

• Not required in MR

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Stereotactic CT scan forSRS

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PHYSICAL COMPONENTS REQUIREDFOR SRT: Relocatable Head Frame

(GTC)

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Image FusionCT

MRI

MRI

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3 piece Mask System,Extends treatment area to T1Set-up errors from 1.7 to 0.9 mm3 indexed differently sized bite platesComplete carbon fiber,Tilt compensation for set-upSuitable for elderly patients & children

Patient positioning accuracy in a thermoplastic mask with upper jaw support.J. Ahlswede et al. AAPM Annual Meeting 2001 Poster Display

Patient Immobilization (SRT)

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PHYSICAL COMPONENTS REQUIREDFOR SRS/SRT

TREATMENT PLANNING SYSTEM:

• Calculates and displaysa 3D dose distributionbased on the patient’sanatomy within thestereotactic frame

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Basic requirements for SRS Dosimetry(Linac Based)

• Accurate localization:– 1mm (angiography,CTA), 2mm (CT, MRI)

• Mechanical Precision: Stability of Linac– Gantry, Collimator & PSA axis of rotation (1mm radius).– Lasers: (2 Lats, 1 @ceiling) Must be parallel and coincide @

isocenter <1mm.

• Accurate and Optimal Dose Distribution:– (<5%). Must be tested in humanoid phantom.

• Patient Safety:– Machine Interlocks. Gantry rotation, Secondary collimators &

Couch motion disabled– Vernier based fine adjustment: allow alignment within ~1m

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Winston Lutz Quality Assurance

Stereotactic Set-up QA. (Linac)

• Phantom Pointer verifies laseraccuracy prior to SRS

• Embossed laser lines for easyalignment with wall lasers

• Integrated tungsten sphere for filmverification

• Irradiation of film at different gantryangles

• Shadow in field center verifiesaccuracy

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QA of Isocenter

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SRX TARGET LOCALIZATION UNCERTAINTY

Machine: 600 CSRX cone: 1.25 cm diameter.SFD: 125 cmFilm type: X Omat L.Monitor units: 4Setup: Coordinates for SRX frames

AP LAT VERtRLPP 0.00 0.00 0.00LTLF 0.00 0.00 0.00

Patient coordinates notation: (supine configuration):A: Anterior; P: Posterior; L: left; R: right; S: superior; I: inferior.Procedure:

1. Laser wall marks verified.2. RLPP set with laser target localization tool (lateral and ceiling lasers in the

middle of the cross).3. Vertical, longitudinal and lateral couch movements locked.4. LTLF used to verify setup (Note: lateral lasers on the middle of lateral laser

crosses. Ceiling laser displaced from center of the cross to the left line andsuperiorly out of the cross as regularly found on the anterior vertical vernier).

5. Laser target tool replaced by target localization ball.6. LTLF removed and film irradiated as indicated in the following table.

Couch 0° 0° 0° 0° 90° 90° 270° 270°Gantry 0° 180° 90° 270° 0° 180° 0° 180°

AP(mm) --- --- +0.1 A -0.7 P --- --- --- ---LR(mm) -0.6 L +0.2 R --- --- +0.5 R -0.8 L 0.0 +1.2 RSI(mm) +1.0 S 0.0 +0.3 S +0.4 S 0.0 +1.0 S +0.4 S -0.5 I

Note: Measurements done on the film (not at isocenter), using Wellhofer WP 700 filmdosimetry program.

Detailed dosimetry results are attached to the original report kept in RadionicsAcceptance Book (2001+).

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QA of Pt Position

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External Target Localization - Pt Position QA:Measure: BRW Localizer frame, on the CT & on theTx. Plan)

RLPP

BRW Localizer Frame

ExternalTarget

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Stereotactic Frames and QA

Frames for SRS Applications:

Brown-Roberts-Wells (BRW)

Tipal

Leksel

Gill-Thomas-Cosman(GTC)

Riechert-Mundinger

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Beam Dose Measurements

• Problem w/ small field dosimetry:– Detector size & Small field dimensions– Lack of equilibrium in lateral charged particles– Large dose gradients in SRS penumbra

• Equipment:– Water tank, polystyrene slabs, ion chamber,diodes,

TLD’s and Film– Detector diameter < 3.5mm(reproduce penumbra ~1mm)

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Measurement Summary

Beam profiles: Films, diodes, plastic scintillators, TLD’s.Detector dimension < 2mm.– Film is the dosimeter of choice. (Very good film processor a must)– Diodes: care w/ angular dependence of response

• TMR’s and Total Output Factors (St=Sc Sp) :

Ionization Chambers, diameters < 3mm.– Ex:PTW Model 23342 Parallel plate Capintec cylindrical, vol= 0.07 cm3

• Absolute Beam Calibration & output factor: according w/approved Protocol

• Gamma Knife: Same dosimeters but max. dosimeterdimensions no greater than 1mm x1mm x 1mm

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Pin-Point Chamber: Waterproof thimble chamber formeasuring in air, water and phantom material: * Vented sensitive volume: 0.125 cm3 and 0.3 cm3

* Suitable for use in water phantoms, w/ photons& electrons. Flat energy response within a wideenergy range.

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Coll=12.5mm

Coll=22.5mm

Coll=30.0 mm

Welhofer

o Laser Film Digitizer(Lumisys)

Film Digitizer

Beam Profiles

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Gamma Knife

Beam profiles

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TMR Curves

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Stereotatic Output Factor Curve(St=Sc Sp)

@ Isocenter, dmax

6 MV

Coll. Diam.:12.5mm to 20.0mm

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Dose Evaluation Tools•Volume Dose

•Surface Dose

•Dose Summary

•Slice Dose

•Dose Volume Histograms

•Tissue-Volume-Ratio (TVR)

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Radiologic Physics Center (RPC)Anthropomorphic Phantom

•Phantom has 2 inserts:

•One for imaging: CT,MRI•One for Dosimetry w/TLD’s andgraphchromic film

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PERSONNELL RESOURCESNumber of Hours Spent Per Treatment On Day Of

SRS/SRT• Radiation Oncologist 3.8 H• Neurosurgeon 3.0 H• Radiologist 0.7 H• Physicist 6.1 H*• Nurse 2.7 H• RTT 2.0 H• *Individual Physicist time; since physics is

involved in all aspects of the procedure total timeis ~ 12 hours

• Larsen et al: Current Radiosurgery Practice: Results of an ASTROSurvey:IJROBP 28(2)523-526, 1994

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IntegrationModular architecture for software

and hardware integration

Upgradeability– Continual software development– Upgrade path for new features

and applications

Radiosurgery1997: m3

2002: NovalisBody

1998: Dynamicconformal arcs

2000: IMRT

1999: ExacTrac

2005: AdaptiveGating

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Dynamic Conformal ArcDynamic Conformal Arcs

• Automatic leaf adaptation to tumorcontour

• Straight-forward arc optimizationwith collision map

• Possible with std. Varian MLC,m3 on Varian or Siemens LinacsBenefits:• Fast, semi-automatic single isocenter

treatment planning• Critical structures are automatically

spared for all beam angles• Most conformal and homogeneous

dose distribution with reducedirradiation of normal tissue

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Conformal mMLC Plan1 Isocenter -6 StaticFields

Dynamic Conformal Arc Plan1 Isocenter - 3 Dynamic Arcs

4.64

3.69 0.

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0.53

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0.5

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1.5

2

2.5

3

3.5

4

4.5

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50% Isodose 90 % Isodose

6 Conf. Beams

3 Dynamic Arcs

Volume of irradiatedNormal Tissue (cm_)

Clinical Results

Courtesy of Universitätsklinkum Charité, Berlin

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Dynamic Arc Radiosurgery Field Shaping: A Comparison with Static Field Conformaland non-coplanar circular arcs. T. Solberg et al. Int. J. Radiation Oncology Biol Physics.Vol 49, No. 5, pp1481–1491, 2001

Dynamic ConformalArc, 5 Arcs (1 isocenter)Conformal Beam,

19 Beams (1 isocenter)

4.0 Gy10.0 Gy18.0 Gy

Circular Arc,8 Isocenters

7.2 Gy18.0 Gy

Clinical ResultsAcoustic Neuroma

Improved normal tissue sparingTight margin around target

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Clinical ResultsAcoustic Neuroma

Homogenous Dose Distribution Greater sparing of normal tissue and risk structures

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1:Ding GX, Duggan DM, Coffey CW.: Commissioning stereotactic radiosurgery beams using bothexperimental and theoretical methods. Phys Med Biol. 2006 May 21;51(10):2549-66.

2: Sánchez-Doblado F, Andreo P, Capote R, Leal A, Perucha M, Arráns R, Núñez L, Mainegra E, LagaresJI, Carrasco E :Phys Med Biol. 2003 Jul 21;48(14):2081-99. Comment in: Phys Med Biol. 2003 Nov7;48(21):L43-5; author reply L46-8. Ionization chamber dosimetry of small photon fields: a Monte Carlostudy on stopping-power ratios for radiosurgery and IMRT beams.

3: Araki F.: Monte Carlo study of a Cyberknife stereotactic radiosurgery system. Med Phys. 2006Aug;33(8):2955-63: Kumamoto University School of Health Sciences, Kumamoto, 862-0976, Japan.Department of Radiological Technology,

4: Cosgrove VP, Jahn U, Pfaender M, Bauer S, Budach V, Wurm RE, Germany Radiother Oncol. 1999Mar;50(3):325-36 : Commissioning of a micro multi-leaf collimator and planning system for stereotacticradiosurgery. Klinik für trahlentherapie, Universitätsklinikum Charité, Berlin,

5: Belec J, Patrocinio H, Verhaegen F.: Development of a Monte Carlo model for the BrainlabmicroMLC.Phys, Med Biol. 2005 Mar 7;50(5):787-99.

6: Li S, Rashid A, He S, Djajaputra D. A new approach in dose measurement and error analysis for narrowphoton beams (beamlets) shaped by different multileaf collimators using a small detector.Med Phys. 2004Jul;31(7):2020-32.

7.Sánchez-Doblado F, Andreo P, Capote R, Leal A, Perucha M, Arráns R, Núñez L, Mainegra E, LagaresJI, Carrasco E.: Ionization chamber dosimetry of small photon fields: a Monte Carlo study on stopping-power ratios for radiosurgery and IMRT beams. Phys Med Biol. 2003 Jul 21;48(14):2081-99.

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8:Deng J, Ma CM, Hai J, Nath R. :Commissioning 6 MV photon beams of astereotactic radiosurgery system for Monte Carlo treatment planning. MedPhys. 2003 Dec;30(12):3124-34.

9: Paskalev KA, Seuntjens JP, Patrocinio HJ, Podgorsak EB.: Physicalaspects of dynamic stereotactic radiosurgery with very small photon beams(1.5 and 3 mm in diameter). Med Phys. 2003 Feb;30(2):111-8.

10: Sikora M,Dohm ),alber M.:A virtual photon source model of an Elektalinear accelerator with integrated mini MLC for Monte Carlo based IMRTdose calculation. Phys Med Biol. 2007 Aug 7;52(15):4449-63. Epub 2007 Jun26.

11: De Vlamynck K, Palmans H, Verhaegen F, De Wagter C, De Neve W,Thierens H.: Dose measurements compared with Monte Carlo simulations ofnarrow 6 MV multileaf collimator shaped photon beams. Med Phys. 1999Sep;26(9):1874-82.

12: Cosgrove VP, Jahn U, Pfaender M, Bauer S, Budach V, WurmRE.:Commissioning of a micro multi-leaf collimator and planning system forstereotactic radiosurgery. Radiother Oncol. 1999 Mar;50(3):325-36.

13: Verhaegen F, Das IJ, Palmans H.: Monte Carlo dosimetry study of a 6 MVstereotactic radiosurgery unit.Phys Med Biol. 1998 Oct;43(10):2755-68

14: Wang L, Li J, Paskalev K, Hoban P, Luo W, Chen L, McNeeley S, PriceR, Ma C.: Commissioning and quality assurance of a commercial stereotactictreatment-planning system for extracranial IMRT.J Appl Clin Med Phys. 2006 Winter;7(1):21-34. Epub 2006 Feb 15.

15: Chaves A, Lopes MC, Alves CC, Oliveira C, Peralta L, Rodrigues P,Trindade A.: Basic dosimetry of radiosurgery narrow beams using MonteCarlo simulations: a detailed study of depth of maximum dose.Med Phys. 2003 Nov;30(11):2904-11.

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16: Crop F, Reynaert N, Pittomvils G, Paelinck L, De Gersem W, DeWagter C, Vakaet L, De Neve W, Thierens H.: Monte Carlo modeling ofthe ModuLeaf miniature MLC for small field dosimetry and qualityassurance of the clinical treatment planning system.Phys Med Biol. 2007 Jun 7;52(11):3275-90

17: 7:Paskalev KA, Seuntjens JP, Patrocinio HJ, Podgorsak EB.:Physical aspects of dynamic stereotactic radiosurgery with very smallphoton beams (1.5 and 3 mm in diameter).Med Phys. 2003 Feb;30(2):111-8.

18:Sikora M, Dohm O, Alber M. :A virtual photon source model of anElekta linear accelerator with integrated mini MLC for Monte Carlobased IMRT dose calculation.Phys Med Biol. 2007 Aug 7;52(15):4449-63.

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Thank you