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 2.5 Alanine Properties 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 1.0 Dose (Gy) 0.5 0.0 -20 -15 -10 -5 0 5 10 15 20 Distance (cm) 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 1.0 Dose (Gy) 0.5 0.0 -20 -15 -10 -5 0 5 10 15 20 Distance (cm) 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