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Delivery Systems I
Alonso N. Gutierrez, Ph.D.Associate Professor
University of Texas Health Science Center San Antonio (UTHSCSA)[email protected]
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Disclosures• Ownership: VeriDos Solutions, LLC
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Learning Objectives• Understand the influence of Gamma Knife on
development of linac-based SRS• Understand the founding principles of conventional linac-
based stereotactic delivery and the rationale for theincorporation of upgrade modifications to linacs
• Understand the impact of add-on equipment toconventional linear accelerators and how it improvesaccuracy and precision in SRT
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Outline of Presentation• Basic stereotactic principles• Early era of linac-based SRS
– Mechanical stability & localization improvements• Beam modifiers• “Early era” image guidance• 6D robotic couches
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Origin of Stereotaxis• Method of locating
points within the brain using an external, 3D frame of reference in order to perform a neurological procedure
*Solberg TD., SBRT, Medical Radiology. 2012
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Linac Stereotactic Localization
Lesion frame Frame linac
Lesion frame linac
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“Key” Physical Stereotactic RT Principles
• Core components– Robust immobilization– Accurate spatial localization– Precise, focused dose distribution– Accurate dose calculation– Ablative “radiosurgical” doses (≥ 8 Gy)
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Immobilization & Localization..
• Frameless IG-SRS• Ease of workflow• Setup accuracy studies
– BrainLAB: 0.76 ± 0.46mm*
*Gevaert T, et al. IJROBP. 85(5). 2012#Pan H, et al. Neurosurgery. 71(4). 2012
• SIG-SRS• Initial study show
comparable clinical outcomes for brain mets#
• Improved patient comfort
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Focused dose distributions• Large # of beams• Non-coplanar • Beam shapers - precision
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Linac-based Radiosurgery?
“If radiation surgery will reach a position as a standard procedure, improved electron accelerators for roentgen production, adapted for the purpose, would seem a most attractive alternative” - Larsson et al. 1974
Larsson B, et al. Acta Radiol 13:512-534. 1974
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Initial Linac Developments
Slide: TD Solberg, Ph.D.
Betti OO, Derechinsky YE (1984) Hyposelective encephalic irradiation with linear accelerator. ActaNeurochir 33: 385–390
1982 – Buenos Aires, Argentina
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“Cyclothrone”• Chair designed since couch weakest
mechanical link– Betti chair (Osvaldo Betti - neurosurgeon)
• Varian Clinac 18• Frame-based system: Talairach
– Attached to chair• Convergent beam delivery via gantry and chair
rotations
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Early Linac-based SRS Limitations
• Major impediments to linac SRT– Mechanical uncertainty (~ 3mm)
• Couch• Gantry
– Dosimetric• Dose rate (<400MU/min)• Small output factors Long tx times
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Late 80’s - Developments
• Significant pioneering efforts• Floor stand development – Wendell Lutz
– Immobilize and precisely position w/o room lasers– Establishment of patient-specific localization test –
aka “Winston-Lutz” test• Floor stand further refined by Siddon and Barth
– Orthogonal radiograph
Lutz W, et al. IJROBP 10(suppl 2) 189. 1984Siddon RL, et al. IJROBP 13. 1987
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Late 80’s - Developments
Lutz W, Winston KR, Maleki N (1988) A system for stereotactic radiosurgery with a linear accelerator. Int J Radiat Oncol Biol Phys 14:373–381
E2E: 2.4mm (CI 95%)
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Overall Geometrical Accuracy
1.0 mm
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• Test MECHANICAL isocentricity of linac
• Align sphere to mechanical isocenter w crosshairs• Cone• MLC
• Irradiate at various couch, collimator & gantry angles• Film• EPID
• Tolerances*• Mean deviation: ≤ 0.75mm• Max ≤ 1.0mm
*Solberg TD, et al. PRO. August. 2011.
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Kim J, et al. JACMP. 13(3). 2012.
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The classic Winston-Lutz test is used to evaluatewhich of the following:
1. Radiation isocenter stability2. Mechanical isocenter stability3. Imaging isocenter stability4. Radiation & imaging isocenter stability
Answer: 2. Mechanical isocenter stability
Ref: Lutz W, et al. A system for stereotactic radiosurgery with a linear accelerator. Int J Radiat Oncol Biol Phys. 14. 1988. 373-381.
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Isocentric arm system
Slide: TD Solberg, Ph.D.
Friedman WA, Bova FJ (1989) The university of Florida radiosurgery system. Surg Neurol 32:334–342
• Precision bearings to control patient and accelerator movements
• Accuracy: 0.2 ± 0.1mm
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First Commercial System• SRS 200 (Philips Medical)
– 1989– Complete package system– U of Florida gimble-type bearing
stand– CT-based TPS– BRW stereotactic frame– Circular collimators (10-32mm)
Patent Drawing: 1993
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Dedicated Commercial SRS Linac
Das IJ, Downes MB, Corn BW et al (1996) Characteristics of a dedicated linear accelerator-based stereotactic radiosurgery-radiotherapy unit. Radiother Oncol 38:61–68
Varian 600SR (1994)
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Varian 600SR• Stereotactic – specific features
• Single energy (6MV)• Redesigned flattening filter => 800MU/min• Primary collimator: 10cm in dia.• Secondary: cylindrical shield• Tertiary: cones• Rotational considerations: range in MU/degree: 0.3‐20
• Mechanical improvements• Lighter treatment head/reduced counter weight• Varian ETR couch• Mechanical isocentricity (WL) < 0.9mm
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Novalis SRS Platform
Slide: TD Solberg, Ph.D.
• 10x10 cm2 FS• 3 – 5.5mm leaves• Small penumbra• Low
leakage/transmission• Circular collimators
• 3‐40mm
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Development of microMLCs
• Lesions not spherical• Irregular shapes require
multiple isocenters / cones– GK “technique”
• Treatment time long• Heterogeneous dose
distributions– Lower ISL prescriptions
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Cone Collimators
• Spherical lesions• Small treatment volumes
– Small brain metastases (<10mm)
– Trigeminal neuralgia
• Improved geometric penumbra
• Faster dose fall off– Reduced brain V12Gy
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microMLCs add-on
Solberg TD, et al. Historical Development of Stereotactic Ablative Radiotherapy. Stereotactic Body Radiation Therapy. Springer. New York. 2012
• 1992 - First mMLC collimators for SRS developed in DKFZ (Heidelberg)
– 3mm wide leaves– Motorized
• 1997 – XKnife system– 15 pairs– 4mm (max field size: 6x6cm2)– v2.0: 27 leaf pair (13.4x10.8cm2)
• 1997 – BrainLAB– 52 leaf– 3mm (14 pairs) / 4.5mm (6pairs)
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microMLCs integrated• Varian HD120 MLC
– 40 x 22cm2
– 60 leaf pairs– 2.5mm (32 pairs)– 5.0mm (28 pairs)– Transmission
• 1.20% (6x)• 1.35% (15x)
Fix MK, et al. Med Phys. 38(10). 2011.
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mMLC-based Delivery
5 isocenters / 20 arcs 1 isocenter / 5 arcs
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mMLC SRS Dosimetric Parameters
Hong LX, et al. Med Phys. 38(3). 2011.
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mMLC SRS Dosimetric Parameters
Hong LX, et al. Med Phys. 38(3). 2011.
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mMLC SRS Dosimetric Parameters
Hong LX, et al. Med Phys. 38(3). 2011.
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mMLC - SBRT Planning
• Lung\Liver SBRT (n=29)– Dif. MLC
• M120• HD120
– Dif. technique• 3DCRT – FF• IMRT - FF• DCA
• Results– Small differences b/w MLCs– Lesion volume size and shape
complexity dependent
Tanyi JA, et al. Radiat Oncol. 4(22). 2009.
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mMLC - SBRT Planning
• Spine lesions– Dif. MLC
• 5.0mm• 2.5mm
– Dif. technique• IMRT - FF• VMAT
• Results– TC (5.7%) & GI (6.3%)
improved– Larger effect on IMRT
over VMAT
Chae SM, et al. Radiat Oncol. 9(72). 2014.
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mMLC Overall Advantages
• 3D conformal– Single isocenter– No need for collimator changes– Increase delivery efficiency– Higher prescription isodose line
normalization (~75%)• IMRT delivery capabilities
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As compared to multiple isocenter, cone-based SRS fortreatment of an irregular lesion, the use of microMLC(mMLC) for collimation employing dynamic arc deliverytechnique will:
1. Decrease delivery time2. Reduces target volume dose inhomogeneity3. Reduces dose to surrounding normal tissue4. All of the above5. None of the above
Answer: 4. All of the above
Ref: Shiu AS, et al. Comparison of miniature multileaf collimation (mMLC) with circular collimation for stereotactic Treatment. Int J Radiat Oncol Bio Phys. 37(3), 679-688. 1997
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When treating a small, spherical cranial lesion, (<10mmin max diameter) with a linac, the key advantage ofusing cone collimation (used as a tertiary collimator)instead of mMLC collimation is:
1. Reduced transmission penumbra2. Improved field flatness by side scatter from cone walls3. Reduced geometric penumbra4. Assure accuracy of beam alignment5. Reduced scatter penumbra
Answer: 3. Reduced geometric penumbra
Ref: Khan F. Physics of Radiotherapy. Lippincott William & Wilkins. 2010. 4th ed.
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Fractionated SRT: Initial Work
Slide: TD Solberg, Ph.D.
Overall accuracy: ~3-4.0mm
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TALON – SRT: Invasive
Accuracy: 0.99 ± 0.28mmSalter B, et al. IJROBP. 51(2). 2001.
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TALON – SRT: Invasive
• n=9 patients• 6 wks fractionated radiotherapy• 6DOF correction
Salter B, et al. IJROBP. 51(2). 2001.
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SRT: Frameless Localization System
• Infrared LED-based monitoring– Res: 0.1mm– 100fps
• Cranial FSRT• Bite-block based• Real-time correction
display
Bova FJ, et al. IJROBP. 38(4). 1997.
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• Frameless system• Thermal plastic mask• Fast localization• 5DOF• n=20 patients• Accuracy
– 0.5 ± 0.3mm
Bova FJ, et al. IJROBP. 38(4). 1997.
SRT: Frameless Localization System
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*Takakura T et al. PMB. 2010.
• ExacTrac System– Two kV x‐rays– Two aSi flat panel detectors
(20.5cm square)– Optical infrared tracking system
• Geometrical accuracy– Isocenter accuracy: 0.35mm*– 6D positional accuracy: 0.07±
0.22mm*
SRT: Frameless, Planar kV Loc.
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Murphy MJ. Med Phys. 24, 857. 1997.*Yu C, et al. Neurosurgery. 52(1). 2004
SRT: Frameless, Planar kV Loc.
• CyberKnife Imaging System– Two ceiling‐mounted kV x‐rays tubes– Two floor‐mounted aSi flat panel
detectors (25cm square)– Orthogonal view geometry– Optical infrared tracking system
• Geometrical accuracy– Positional accuracy: 0.7± 0.3mm*
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SRT : Volumetric Loc.
Isocenter localization errors*X: 0.5 ± 0.7mmY: 0.6 ± 0.5mmZ: 0.0 ± 0.5mm
OBI XVI
*Kim J, et al. IJROBP. 79(5). 2011.Wiehle R, et al. Strahlenther Onkol. 5. 2009
Isocenter localization errors*R: 1.1 ± 0.6mm
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Initial 6DOF Corrections
• Rotation corrections – cranial mounts
• Adoption of extra-cranial IG localization necessitates 6D correction– Translations– Rotations
• Reduced residual localization errors
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6 DOF Couch - ProTura™
• Aftermarket robotic couch• Civco Medical Solutions• Rotations about machine
isocenter• Correction limits
– 3° pitch, roll, & yaw– ±50mm lat. & long.– ±25mm vert.
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6 DOF correction – SRS Implications
• Protura™ accuracy– Lat: 0.2mm– Vert: 0.3mm– Long: 0.4mm– Pitch: 0.1°– Roll: 0.2°– Yaw: 0.1°
• n=28 pts (63fxs)
Dhabaan A, et al. JACMP. 13(6). 2012.
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6 DOF correction – SRS Implications• Protura™ w NovalisTx (frameless SRS)• N=113 pts (160 targets)• Initial CBCT
– 1.03 °± 0.8 (yaw), 1.16°± 0.9 (roll) and 0.9°± 0.7 (pitch)• Verification CBCT
– 0.37°± 0.6 (yaw), 0.27°± 0.28 (roll) and 0.24°± 0.29 (pitch)
• Reduce residual errors– ≤ 0.4° rotational– ≤ 0.7mm translational
Dhabaan A, et al. SU-E-T-369. AAPM 2014.
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6 DOF Couch - HexaPOD
• Elekta Solution• Correction limits
– 3° pitch, roll, & yaw– ±30mm lat. & long.– ±40mm vert.
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6 DOF correction – Accuracy
• HexaPOD™ accuracy
Meyer J, et al. IJROBP. 67(4). 2007.
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6 DOF Couch – ExaTrac Couch
• BrainLAB Solution• Accuracy
– Lat : 0.06±0.15mm– Vert: 0.06±0.12mm– Long: 0.06±0.10mm– Roll: -0.05±0.14°– Pitch: 0.02±0.10°– Yaw: -0.01±0.07°
Takakura T et al. PMB. 2010.
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6 DOF Couch – Perfect Pitch
• Varian Solution• Correction limits
– ±3° pitch, roll, & yaw– ±50mm lat. & long.– ±25mm vert.
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The integration of a 6 degree-of-freedom treatmentcouch as compared to a 3 degree-of-freedom treatmentcouch in modern image-guided SRT delivery systemswill:
1. Improve mechanical stability of couch2. Reduce mechanical accuracy of couch3. Reduce residual setup errors4. Allow for faster patient repositioning
Answer: 3. Reduce residual setup errors
Ref: Ma J, et al. ExacTrac x-ray 6 degree-of-freedom image-guidance for intracranial non-invasive stereotactic radiotherapy: Comparison with kilo-voltage cone-beam CT. Radiotherapy and Oncology. 93. 2009. 602-608.
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Summary/Conclusion
• Linac-based stereotactic techniques have evolved over time to improve accuracy and precision of radiation delivery
• Additive development of improved components have enabled the creation of robust, dedicated stereotactic delivery systems
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Thank you for your time and attention.