SRS/SRT with Tomotherapy
Thomas Rockwell Mackie Professor Depts. Of Medical Physics, Human Oncology, and Engineering Physics University of Wisconsin Madison WI 53706
[email protected] Conflict of Interest Statement: I have financial interest in TomoTherapy Inc. Helical Tomotherapy
• IMRT and SRS Delivery • CT Guidance • Image Database • Record and Verify • Planning System • Delivery QA • Fully Integrated
Designed for Simple or Complex Treatments Tomotherapy was Designed for IGRT and IMRT
Helical fan-beam IMRT or SRS delivery is fast, effective, and simple. CT is the most important imaging modality for radiotherapy and SRS. Linac on a CT is better than a CT on a linac. » ring gantry is more stable than a C-arm gantry. » CT gantry allows faster rotation. » no possibility of rotational collisions. » coplanar delivery is simpler. Single energy sufficient. Simple binary MLC modulating the fan beam. Accurate CT couch. Helical Tomotherapy Unit
Gun Board Linac Control Computer Circulator
Magnetron
Pulse Forming Network and Modulator Data Acquisition System High Voltage Power Supply Beam Stop Detector From TomoTherapy Inc. How Tomotherapy Works
Continuous Rotation Binary Collimation Modulated Helical Delivery into Scintillation Fluid Major Differences of Tomotherapy from C-arm Linacs
Field Light: no field light ODI: no optical distance indicator MLC: binary modulator Collimator Rotation: no collimator rotation Accessories: no accessories Couch: no rotation, continuous translation Lasers: green (fixed) and red (movable) lasers Field Profile: triangular shape (no flattening filter) Modulation: nearly continuous intensity modulation Number of Fields: 51 arcs segments instead of 5 to 9 fields CT Imaged: true CT scanner used for beamline QA Linac Alignment
Linac
Alignment Jig Longitudinal (In-Out) Alignment Test
• Film Plane Offset From Central Axis • One Irradiation From Above • Second From Below MLC Center of Rotation Tongue and Groove Offset Irradiation Of Leaves 32 and 33 Tongue and Groove Irradiation Of Leaves 28 and 29 Gantry Isocenter
Film With Buildup At Gantry Isocenter
Pointing to MLC Center Tongue and Groove Irradiation Of Leaves28 and 29 Tongue and Groove Image from Leaves 28 and 29 When Tongue and Groove Gantry Pointing Image from Leaves Down 28 and 29 When Gantry Pointing Tongue and Groove Up Image from Leaves 32 and 33 When Gantry Pointing Down MLC/Center of Rotation X1 X2 X1 = 25.1 mm 100.0 X2 = 24.7 mm 80.0 Diff = 0.4 mm Offset = 0.2 mm 60.0
40.0 Percent (%)
20.0
0.0 -80.0 -60.0 -40.0 -20.0 0.0 20.0 40.0 60.0 80.0 Distance (mm) MLC Center of Rotation
Gantry 65 MLC Offset = 0.01 mm
Transverse Dose Profile (25mm Beam, Off-Axis Tumor)
120 calc meas 100
80
60
40 Normalized Dose (%) Dose Normalized
20
0 -15 -10 -5 0 5 10 15
Distance Off-Axis (cm) MLC Center of Rotation
Gantry 75 MLC Offset = 0.23 mm
Transverse Dose Profile (25mm Beam, Off-Axis Tumor)
120 calc meas 100
80
60
40 Normalized Dose (%) Dose Normalized
20
0 -15 -10 -5 0 5 10 15
Distance Off-Axis (cm) MLC Center of Rotation
Gantry 78 MLC Offset = 0.31 mm
Transverse Dose Profile (25mm Beam, Off-Axis Tumor)
120 calc meas 100
80
60
40 Normalized Dose (%) Dose Normalized
20
0 -15 -10 -5 0 5 10 15
Distance Off-Axis (cm) MLC Center of Rotation
Gantry 64 MLC Offset = 0.96 mm
Transverse Dose Profile (25mm Beam, Off-Axis Tumor)
120 calc meas 100
80
60
40 Normalized Dose (%) Dose Normalized
20
0 -15 -10 -5 0 5 10 15
Distance Off-Axis (cm) MLC Center of Rotation
Gantry 71 MLC Offset = 1.01 mm
Transverse Dose Profile (25mm Beam, Off-Axis Tumor)
120 calc meas 100
80
60
40 Normalized Dose (%) Dose Normalized
20
0 -15 -10 -5 0 5 10 15
Distance Off-Axis (cm) MLC Center of Rotation
Gantry 60 MLC Offset = 1.21 mm
Transverse Dose Profile (25mm Beam, Off-Axis Tumor)
120 calc meas 100
80
60
40 Normalized Dose (%) Dose Normalized
20
0 -15 -10 -5 0 5 10 15
Distance Off-Axis (cm) Slice Width Check
Irradiate film with all three slice widths (all leaves open) Find FWHM Compare results to the nominal slice widths and ensure that they agree to within 1mm
From Emilie Soisson, Hoag Hospital, CA Test of Synchrony of Couch and Gantry
Gantry rotation – central leaves open at 0°, 120° and 240°
Couch y-drive direction
Two films positioned axially 6 Tests synchrony of cm apart on a couch couch and gantry. Angular Positioning Results
-3 cm +3 cm Test of Couch Positioning
100 .. 80
60
40
20 % max optical density
0 -100 -50 0 50 100 distance along couch drive direction (mm) Alanine Dosimetry Project of Simon Duane, NPL and Stefaan Vynckier, Brussels
NPL
Alanine Properties 2.5
2.0 Dose (Gy) Dose 18-Nov (Gy) alanine dose 18-Nov (Gy) • Water equivalent 1.5 • 10 Gy exposure required 1.0 • Need 1 day to stabilize • Read out with a spectrometer 0.5
0.0
-15 -10 -5 0 5 10 15 Summary of Data Alanine data are averaged over 2-5 adjacent pellets
Machine/beam UCL dosimeter UCL / NPL alanine
Tomo / static 5 cm thick, 1.5 cm deep A1SL 1.000
Tomo / static 5 cm thick, 5 cm deep A1SL 1.002
SL25 / 6MV 10x10 cm, 5 cm deep NE2571 1.002
SL25 / 6MV 10x10 cm, 5 cm deep NE2571 1.001
Tomo / helical, 2.5 cm width, in target A1SL 1.015
Tomo / helical, 2.5 cm width, in target A1SL 1.012
Tomo / helical, 1.0 cm width, in target A1SL 1.002
Tomo / helical, 1.0 cm width, in target A1SL 1.005
Tomo / helical, 5 cm width, in target A1SL 1.009
Tomo / helical, 5 cm width, in target A1SL 1.011
From Stefaan Vynckier, St. Luc Hospital, Brussels Gortec IMRT Test Phantom
Point 1: Isocenter
Point 2: Spinal cord isocenter
Point 3: Spinal cord cranial
Point 4: PTV T R
Point 5: PTV T R cranial
Point 6: PTV N L
Point 7: PTV N L caudal Courtesy M. Tomsej, St. Luc, Brussels Some Preliminary Audit Results
Dm/Dc=f(CENTER) per meas. pt
1.2
1.15
1.1 isocenter 1.05 spinal cord iso
c spinal cord cranial
/D 1 PTV T D m
D PTV T D cranial 0.95 PTV N G PTV N G caudal 0.9
0.85
0.8 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 CENTER Off-Axis Test Case “Cheese” Phantom
Measure “ Cheese” plane and Phantom point dose used for QA at the same time measurements
Film Plane Phantom can be rotated or turned to acquire any orthogonal plane On-Axis and Off-Axis Absolute Dose Film and Ion Chamber Absolute Dose
Delivered Dose: 2.5cm Treatment Beam
2.5 On-Axis Tumor Off-Axis Tumor
2.0
1.5
Dose (Gy) 1.0
0.5
0.0
-20 -15 -10 -5 Distance0 (cm) 5 10 15 20
Negligible Change in the Dose with a Different Slice Width On-Axis and Off-Axis Absolute Dose Film and Ion Chamber Absolute Dose
Delivered Dose: 1.0cm Treatment Beam
2.5 On-Axis Tumor Off-Axis Tumor
2.0
1.5
Dose (Gy) 1.0
0.5
0.0
-20 -15 -10 -5 Distance0 (cm) 5 10 15 20
Negligible Change in the Dose with a Different Slice Width Radiotherapy + SRS + Special Treatments
Total Bone Marrow Standard Treatments Irradiation Multiple Targets at the Same Time Prostate Breast
Tumor Superficial Stereotactic Retreatments Treatments Radiosurgery Head and Neck Lung Modulation and Angles are Both Beneficial
Traditional SRS Angles
CyberKnife® TomoTherapy® how many many how
Conformal RT Conventional IMRT
how much Modulation Tomotherapy Geometry
Front view Jaws Side view Define beam width (W)
W
W Binary MLC isocenter
W Image Guided Patient Setup Via pre-treatment images
patient image beams
Locate tumor in room…
Tomo Image = beams TomoTherapy Targeting
Tumor
TomoCT IsocenterIsocenter
Objective:
Reproduce planning CT geometry on Hi-Art
Tumor stays at same location relative to isocenter Image Guided Stereotactic TomoTherapy
Images Courtesy of Chet Ramsey, Ph.D. TCSC, Knoxville, TN Approximate Delivery Times (1 cm beam) Collimator width: 1 cm Modulation factor: 1.5 Pitch: 0.1 e.g. 18 Gy to 2 cm PTV takes approx. 20 mins Dose rate at target: 4 cGy/min PTV RP Length (cm) 321 4 5 =Rotation Period # Rotations 3020 40 50 60 Dose (Gy) RP (s) 2 15.0 5.0 7.5 10.0 12.5 15.0 4 15.0 5.0 7.5 10.0 12.5 15.0 6 15.0 5.0 7.5 10.0 12.5 15.0 8 18.0 6.0 9.0 12.0 15.0 18.0 10 22.5 7.5 11.3 15.0 18.8 22.5 12 27.0 9.0 13.5 18.0 22.5 27.0 14 31.5 10.5 15.8 21.0 26.3 31.5 16 36.0 12.0 18.0 24.0 30.0 36.0 18 40.5 13.5 20.3 27.0 33.8 40.5 20 45.0 15.0 22.5 30.0 37.5 45.0 22 49.5 16.5 24.8 33.0 41.3 49.5 24 54.0 18.0 27.0 36.0 45.0 54.0 sec/cm/Gy 45.0 33.8 30.0 28.1 27.0 Simple and Complex Targets
20 Gy prescription dose
Even more conformal!
Conformity index: 1.10 Conformity index: 1.06 Delivery time: 11.5 mins Delivery time: 21 mins Pitch: 0.1 Pitch: 0.1 Modulation factor: 1.5 Modulation factor: 2.4 How Small can Tomo Treat?
1 cm target 0.6 cm target 20 Gy prescription dose
Vpresc/VPTV 19-24 Gy PTV dose 19.5-23 Gy PTV dose Still very good! CI = 1.10 CI = 1.14
TomoTherapy AVM Case
AVM avoid
chiasm Highly conformal dose distribution Fast, isotropic dose falloff
18Gy 9Gy 3Gy Very conformal dose sIMRT Tomotherapy (5mm MLC)
16 patient study Index Mean and Standard Deviation sIMRT Tomotherapy
Conformity index CI 1.36±0.17 1.27±0.10 Gradient score index GSI 23.97±19.84 44.22±14.05
More Sharper More City of Hope National Medical Center conformal gradient consistent Metastasis Case (1.6 cc CTV, 17 Gy single frac.)
Faster dose falloff TomoTherapy
Conformity index: 1.82
Dose gradient: More conformal dose 9.35%/mm
5 conformal arcs
Conformity index: 2.30
Dose gradient: 7.27%/mm
City of Hope National Medical Center Meningioma Case (29 cc CTV, 16 Gy single frac.)
Faster dose falloff TomoTherapy
Conformity index: 1.35
Dose gradient: More conformal dose 3.59%/mm
7-field IMRT 3 mm MLC leaves
Conformity index: 1.82
Dose gradient: 2.96%/mm City of Hope National Medical Center Mean Dose to Normal Brain
Yartsev et al, Radiotherapy and Oncology 74 (2005) 49-52 Study Design Planning study for: 5 acoustic neuromas, 5 meningiomas, 2 pituitary adenomas
Comparison between: Protons, arc SRS, 3D Conformal, Conventional IMRT, Helical Tomotherapy Mean Dose is Invariant with Photon Technique
Mean Brain Dose:
Tomo 6.7% Mean dose (mean dose is Photons SRS 7.3% proportional to integral dose) 3DCRT 6.7% is similar to or less than other IMRT 8.0% photon techniques Protons PSP 2.2% SSP 1.8% Tomotherapy Gives Reduction in High Dose Region in Brain
Brain volume receiving more than 20% of mean target dose:
Tomo 3.7% Lowest volume of significant dose among photon Photons SRS 7.8% techniques 3DCRT 9.8% IMRT 11.2% Protons PSP 3.6% SSP 3.2% Whole Brain + Multiple Mets Simultaneously
Bauman et al, Am. J. Clin. Oncol. 2007; 30: 38-44 Simultaneous In-Field Boost
30 Gy For “Free” Organ Dose (Gy)Organ
Prescribed Dose to PTV (Gy)
Courtesy Glen Bauman, London Regional Cancer Center Whole Brain + Multiple Mets - Hippocampus
Hippocampus Whole Brain CTV
Mets
Eyes
Courtesy Wolfgang Tomé, University of Wisconsin Delivery QA Delivery Verification in Coronal Plane
Brain Metastasis
Avoidance Region
Gamma-Map
Courtesy Wolfgang Tomé, University of Wisconsin Simultaneous Treatment of Multiple Metastases
TomoTherapy Conventional Few Field IMRT Single Fraction SRS Case
100% - 50% in 4.5 mm (11% /mm) 16 minutes for 15 Gy delivery IMAT: 4 x 200 deg sagittal arcs
15-30 Gy in oral cavity!
Tomo Modulation spares the eye!
No dose! Residual Registration Error
Coarse (6mm) slices
<0.5 mm error Normal (4mm) and Fine (2mm) slices Stereotactic Radiosurgery Hardware Developments
Integra Radionics has developed adaptors to enable fixation of their industry- standard stereotactic head rings to the TomoTherapy Hi-Art couch top Radionics Head Rings
TLC Pediatric CRW Invasive HR Non-Invasive HR GTC Non-Invasive HR
BRW Localizer Radionics Head Ring Adaptors
CT Couch Adaptor Tomo Couch Adaptor
Affixes via universal side clamp Affixes via indexing holes CRW and GTC Mounted on Couch GTC Frame Conventional SRS with Invasive Fixation
Immobilize Planning scan Plan Planning, target localization
Hours…
Setup via lasers/frame
Treat Treat SRS with Non-Invasive Fixation and TTomoomo Image Guidance
Immobilize Planning scan Plan Planning
Days…
Immobilize Setup via image guidance Treat Treat Pre-registration Transverse slice Post-registration Transverse slice Pre-registration Coronal slice (rods 7,8,9) Post-registration Coronal slice (rods 7,8,9) Tomo and IMAT Comparison for Body SRT IMAT mean lung dose of 929 cGy
IMAT with 4 IMAT max cord arcs dose of 470 cGy IMAT mean cord dose of 225 cGy
PTV Tomo mean lung Revised GTV Helical dose of 765 cGy TomoTherapy Tomo max cord
Lower Lung Lung dose of 195 cGy Dose Volume Tomo mean cord Lower Cord Spinal Cord dose of 82 cGy Dose Lung (Case 1)
Revised Helical TomoTherapy Plan
Compared to IMAT plan: Lung mean dose reduced by ~17.6% Spinal cord max dose reduced by ~58.5% Spinal cord mean dose reduced by ~63.5% Spine Plan
CyberKnife: TomoTherapy: 12.5 mm and 20 mm cones 6 mm x 10 mm beamlets
Continuous 80 beams, 360 degree none from rotations posterior Spine Plan
80% isodose 95% volume = 16 Gy gets 20 Gy
40 min beam time 40 min delivery plus time 80 direction for changes 4000-beamlet plan plus collimator change Direct Comparison
Hi-Art + CyberKnife + Conformity via helical IMRT Intra-fraction position checks Fast delivery due to of bony anatomy or markers continuous beam Tracking of small lung/liver Soft tissue image guidance via lesions via “Synchrony” 3D MVCT Non-coplanar beams No need for fiducial markers Dose guidance via dose calculation on 3D MVCT image Hi-Art – CyberKnife – No tracking or gating for Less dose conformality respiratory motion Only 2D image guidance Only coplanar beams Need implanted markers for soft tissue targeting Very slow delivery Summary
Highly conformal treatment with fast dose gradient due to highly modulated, arc-based delivery. Designed to be a CT-guided solution to IMRT, SRS or Special Procedures. Quality assurance is different but easy. Faster SRS especially for multiple metastases. Setup ideal for non-invasive setups. Compatible with industry-standard radiosurgery head rings for invasive or non-invasive immobilization. Cranial SRS or SRT and Body SRT typically as good or better than conventional technology.