Tomotherapy Thomas Rockwell Mackie Tomotherapy Research Group Depts. Of Medical Physics, Human Oncology and Biomedical Engineering University of Wisconsin Madison WI 53706 Phone: (608) 262-7358 Email: trmackie@facstaff.wisc.edu Web: www.madrad.radiology.wisc.edu Contributors to this Talk • • • • • • • • • • Gustavo Olivera Paul Reckwerdt Jeff Kapatoes Ken Ruchala John Balog Richard Schmidt Ed Fitchard Dave Pearson Eric Schloesser Ray MacDonald • • • • • • • • • • Robert Jeraj Minesh Mehta Mark Ritter Jack Fowler Harry Keller Weiguo Lu Jeni Smilowitz Wolfgang Tomé Rufus Scrimger Lisa Forrest Financial Disclosure In addition to a University of Wisconsin Professor, I am a co-founder of TomoTherapy Inc. (Middleton WI) which is participating in the commercial development of helical tomotherapy. TomoTherapy’s 1,400 m2 Middleton facility. www.tomotherapy.com Outline • • • • • • • • Optimization ® IMRT ® Conformal Dose Distributions Sequential (or Serial) Tomotherapy (NOMOS Peacock™) Clinical Helical Tomotherapy Unit Dosimetry of Helical Tomotherapy Examples of Tomotherapy Dose Distributions Megavoltage Computed Tomography (MVCT) Adaptive Radiotherapy Clinical Implications Optimization ® IMRT ® Conformal Dose Distributions Anders Brahme first showed that intensity modulated fields of radiation would lead to more conformal dose distributions that would spare normal tissue. IMRT Using Conventional MLC’s Siemens Varian Elekta Sequential Tomotherapy The First Form of IMRT NOMOS Peacock System X-Ray Beam Binary MLC Leaves Binary Multileaf Collimator Courtesy: NOMOS Corporation Simulated Annealing Optimization MIMiC Multileaf Intensity Modulating Collimator From Bruce Curran, NOMOS Individual leaf controls opening 68 Gy 60 Gy 50 Gy 30 Gy Bi-Lateral 3D-CRT From Bruce Curran, NOMOS 85Gy 70Gy 60Gy 50Gy 30Gy 7-Field IMRT (Planned with Corvus) Sequential Tomotherapy (Nomos Peacock) From Bruce Curran, NOMOS GTV Dose Volume Histogram 120 100 Volume (%) 80 GTV_Corvus GTV_Peacock 60 GTV_3DCRT GTV_Bilateral 40 20 0 0 20 40 60 80 100 Dose (Gy) From Bruce Curran, NOMOS Chiasm Dose Volume Histogram 120 Chiasm_Corvus 100 Chiasm_Peacock Chiasm_3DCRT Volume (%) 80 Chiasm_Bilateral 60 40 20 0 0 20 40 60 80 100 120 Dose (Gy) From Bruce Curran, NOMOS Brain stem Dose Volume Histogram 120 Stem_Corvus Stem_Peacock 100 Stem_3DCRT Stem_Bilateral Volume (%) 80 60 40 20 0 0 20 40 60 80 100 Dose (Gy) From Bruce Curran, NOMOS Parotid Dose Volume Histogram 120 Parotid_Corvus Parotid_Peacock 100 Parotid _3DCRT Parotid_Bilateral Volume (%) 80 60 40 20 0 0 20 40 60 80 100 Dose (Gy) From Bruce Curran, NOMOS Role of Beam Configuration All results for 7 beam directions except where otherwise noted. Detailed dependency upon the number of beam directions is shown in the next table. Dependency Upon Number of Beam Directions Mean Dose Total Integral to the Dose Region at Risk 0.124 Minimum Dose Covering 90% of the Target (1.0=max) 0.747 0.488 2733 0.318 0.090 0.814 0.215 2564 7 0.242 0.064 0.867 0.206 2597 9 0.222 0.064 0.855 0.192 2599 11 0.202 0.058 0.879 0.186 2570 15 0.187 0.053 0.908 0.180 2542 21 0.176 0.049 0.912 0.171 2545 33 0.151 0.038 0.933 0.155 2544 Number of Beam Directions Objective Function Value Standard Deviation in the Target Dose 3 0.665 5 Nasopharyngeal Example In this case the primary goal was to avoid the parotid and spinal cord. With the same amount of avoidance, the 45 angle delivery (tomotherapy) provided a more homogeneous delivery. Re-Engineering Radiotherapy • • • • • • • • • Equipment and processes re-engineered for IMRT Integration of planning, delivery and verification Better leaf resolution Simple MLC’s More beam directions Single energy photon beam Better primary shielding Tomographic verification Helical tomotherapy was the result Helical (Spiral) Tomotherapy Ring Gantry Linac CT Detector CT Couch Helical Fan Beam Helical Scanning Animation of Helical Delivery 64 Leaf Binary MLC Close-Up Movie Clips of the MLC Being Tested Close-Up UW Clinical Helical Tomotherapy Unit Siemens Linac GE CT Detector Siemens RF System GE Gantry May 2000 at UW Physical Sciences Laboratory, Stoughton WI Siemens 6 MV Linac System Linac and Gun Control RF System Clinical Installation Finished January 16, 2001 at UW Radiotherapy Clinic Major Specifications • • • • • • • • • • • 6 MV Siemens linac Up to 8 Gy/min @ axis 85 cm diameter gantry bore 64 leaves with 6.25 mm resolution @ axis 4 cm x 40 cm maximum field @ axis Slice field width from 5 mm to 40 mm @ axis Minimum beamlet size 5 mm x 6.25 mm @ axis Xenon CT detectors with per pulse acquisition 0.25 mm precision CT couch Leaves 10 cm thick, 95% tungsten alloy Primary collimator 22 cm thick 95% tungsten alloy Fan Beam Characteristics • The fan field width along the longitudinal direction is continuous from 5 mm to 50 mm. • There is no field flattening filter in the beam and so the beam has a higher intensity along the center as compared to either end. • The beam without filtration is like the output from a CT “Bowtie Filter”. 1 cm Image Digitized from Kodak XV Film 40 cm Profile Along Length of a 1 cm Wide Fan Beam Transverse Profile 120 100 Dose (%) 80 60 40 20 0 -240 -180 -120 -60 0 60 Distance (m m ) 120 180 240 Monte Carlo Model of the Treatment Head Target Electron Stopper Electron Beam from the Accelerator Beam Hardener Monitor Chamber Primary Collimator and Jaws Photon Spectrum 1.0 Tomotherapy (6MV) 2100 Clinac (6MV, Stanford) Spectrum [%] 0.8 0.6 0.4 0.2 0.0 0 1 2 3 4 Energy [MeV] 5 6 Clinac 2100 Monte Carlo data courtesy of Dr. Charlie Ma For the same incident energy, tomotherapy has a harder spectrum due to its beam hardener and absence of a field flattening filter. Off-Axis Energy Dependence 0.040 0.035 0-5 cm 5-10 cm 10-15 cm 15-20 cm 0.025 0.01 Photon spectrum Photon spectrum 0.030 0-5 cm 5-10 cm 10-15 cm 15-20 cm 0.020 0.015 0.010 1E-3 0.005 0.000 0 1 2 3 4 Energy [MeV] 5 6 7 0 1 2 3 4 5 6 Energy [MeV] Tomotherapy has no off axis hardening because of no flattening filter. Simplicity of Tomotherapy Tomotherapy Conventional RT Designed for Image-Guided IMRT Single Photon Energy Designed for Conventional RT Processes Dual Mode Multiple Energy Simple MLC Complex MLC No Collimator Rotation Collimator Rotation No Couch Rotation One or Two Axes of Couch Rotation 2D Electronic Portal Imager Simple CT Detector System Integration Multi-Component Integration Conventional Plan to Treat Lung Cancer 98 % 70 % 50 % 40 % 20 % Tumor Spinal Cord Tomotherapy Plan to Treat Lung Cancer 80 % 70 % 50 % 40 % 20 % Tumor Spinal Cord Tomotherapy Decreases Mean Dose to Spinal Cord 25 25 Conventional 3D 3D plans Tomotherapy 20 Tomotherapy Dose (Gy) 20 15 10 5 0 5 0 P1 1 2 P2 3 P3 Patient Case 4 P4 P5 5 Mean Mean Prostate Carcinoma Cumulative Dose Dose Rate 0 to 30% 30 to 90% 90 to 100% Percentage of Rectal Volume Receiving High Doses 25 20 % of volume exceeding 15 stated dose >60 Gy >70 Gy 10 5 0 Conventional 3D Conventional 3D Tomotherapy Tomotherapy Breast Carcinoma Case: Tomotherapy Movie Dose Rate Cumulative Dose Contr. breast IMC nodes Tumor Heart Left lung Right lung Spine ROI slice 47 0 to 30% 30 to 90% 90% or higher Tomotherapy for GBM Treatments Isodose Lines 100% 90% 80% 50% Targets GTV Hypoxic Proliferative Tomotherapy for GBM Treatments Dose Rate Cumulative Dose 0 to 50 % 50 to 75% 75 to 85 % 85 to 95 % 95 to 100% Mesothelioma ROI slice 27 Dose Rate Cumulative Dose 31 Distributions Slice 36 Tomotherapy Slice Dose Slice 27 50 % 80 % 90 % 50 % 80 % 90 % 50 % 80 % 90 % Adaptive Radiotherapy 3-D Imaging Deformable Dose Registration Optimized Planning MV CT + Image Fusion Dose Reconstruction Treatment With Delivery Verification Delivery Modification Why CT Before Delivery is Necessary CT Images Acquired Daily The slices were rotated and translated to align the bony anatomy as best as possible. Original CTV Courtesy Di Yan and Marcel Van Herk Interfraction Movement of the Breast Electronic portal image of the breast treated using a compensator. Each frame is a different day. From Dr. Jason Sohn Mallinckrodt Institute MVCT of CIRS Phantom 0.2% 4.3% -2.4% -54.1% 5.2% -4.8% 11.7% 51.2% 7 cGy -81.0% 3.5 cGy 1.75 cGy MVCT of RMI Phantom 1.50 mm 1.25 mm 1.00 mm 0.8 mm 1.50 mm 1.25 mm 1.00 mm 0.8 mm MVCT Calibration Curve Image Density Electron density (red), physical density (violet) Rando Phantom Megavoltage CT (MVCT) Head Pelvis Rando Phantom MVCT Slice-by-Slice Traversal Through Volume Dose for Scan = 3 cGy Dose for Scan = 5 cGy Automated Fusion of kV and MV CT Sets Fusing Prostate CT’s Acquired on Two Different Days X-offset= 4.20 cm Roll-offset= 32.50 deg Y-offset= 4.20 cm Pitch- offset= 8.90 deg Z-offset= 2.60 cm Yaw- offset= 14.70 deg Adaptive Radiotherapy 3-D Imaging Deformable Dose Registration Optimized Planning MV CT + Image Fusion Dose Reconstruction Helical Tomotherapy Delivery Modification Delivery Modification • There are two potential ways to adjust the patient setup: – Adjust the patient. – Adjust the beams. • It may be easier and more reliable to move the beams to the patient. • It may be possible in tomotherapy to alter the leaf delivery pattern. Optimized 50 % 80 % 95 % Delivery Modified 50 % 80 % 95 % 1.42 cm offset 1cm x-offset 1cm y-offset Adaptive Radiotherapy 3-D Imaging Deformable Dose Registration Optimized Planning MV CT + Image Fusion Dose Reconstruction Helical Tomotherapy Delivery Modification Dose Reconstruction • Dose reconstruction uses transmission data acquired during treatment and the megavoltage CT to determine the dose distribution delivered that day. • Dose reconstruction provides a way to directly compare the plan with the result. Example of Dose Reconstruction ROI’s (slice 29) L. eye MV CT (slice 29) Target R. eye Brain 8.5 deg. Shift Dose Reconstructed Using MV CT The reconstructed dose reveals that the dose distribution is rotated toward the left eye and underdosing the target volume. Optimized Reconstructed Adaptive Radiotherapy 3-D Imaging Deformable Dose Registration Optimized Planning MV CT + Image Fusion Dose Reconstruction Helical Tomotherapy Delivery Modification Deformable Dose Registration • Deformable dose registration uses a mechanical deformation model along with matched contours and points from two image sets to register them. • Deformable dose registration allows the dose from each fraction to be added up properly. Adaptive Radiotherapy 3-D Imaging Deformable Dose Registration Optimized Planning MV CT + Image Fusion Dose Reconstruction Helical Tomotherapy Delivery Modification Image of Regret 0 to 3 mm(%) 6 to 9 mm(%) 3 to 6 mm(%) 9 to 12 mm(%) Adapted Dose Distribution Dose to deliver to correct regret. Incorrect +Perfect Adapted Non - Adapted 0 to 3 mm(%) 6 to 9 mm(%) Incorrect +Corrected 3 to 6 mm(%) 9 to 12 mm(%) 0 to 3 mm(%) 6 to 9 mm(%) 3 to 6 mm(%) 9 to 12 mm(%) Clinical Implications • More complex target volumes can be delivered and still spare critical volumes. • Complex prescriptions or “dose painting”. • Higher dose/fraction can be delivered to the tumor and still have low dose and dose/fraction to critical tissues. • Conformal avoidance. • More accurate setup of the patient. • Better verification that delivery is correct. • Have a basis to repair dose distributions. • Adaptive radiotherapy. Other Innovative Treatments Tomotherapy Will Enable • Stereotactic radiotherapy (and radiosurgery) to the body. • Irradiate entire nodal chains with conformal avoidance. • Repairing the dose distributions from other modalities, e.g., poor seed implants. • Combined brachytherapy and IMRT. • Bone marrow ablation while sparing visceral organs. • Whole-skin irradiation using IMRT. • Probability-based prophylactic radiotherapy. • Swiss-cheese-like dose distributions in normal tissue (3-D grid therapy). • Great change in breast radiotherapy. Increased Throughput Possible • Integration of planning, delivery and verification. • Potentially easier to commission and calibrate. • Dose reconstruction eliminates need for on-going patient-specific dosimetry measurements. • Fewer planning decisions and optimization may be automated. • High dose rate (8 Gy/min). • Higher dose/fraction more feasible because normal tissue can be more easily avoided. • Easier patient setup. • No couch rotation reducing possibility of collision. • Tomographic verification images are more easy to interpret than planar portal images. • Impact of delivery errors can be reduced. • Increased primary collimation so less staff irradiation per patient. Conclusions • Helical tomotherapy is the marriage of a linac with a CT scanner. • Helical tomotherapy can deliver highly conformal dose distributions. • Megavoltage CT is sufficient for verification of the setup. • Dose reconstruction and deformable registration determines the dose actually delivered. • Adaptive radiotherapy ensures that the whole course of therapy is delivered correctly. • Tomotherapy provides image-guidance for the whole chain of radiotherapy processes.
0
advertisement
Related documents
Download
advertisement
Add this document to collection(s)
You can add this document to your study collection(s)
Sign in Available only to authorized usersAdd this document to saved
You can add this document to your saved list
Sign in Available only to authorized users