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TomoTherapy Document Transcript

  • 1. Scope of Talking TomoTherapy Overview of Tomotherapy Tomotherapy Process Clinical Application Concerned Issues Lalida Tuntipumiamorn Division of Radiation Oncology Future Direction Department of Radiology, Faculty of Medicine, Siriraj Hospital MAHIDOL UNIVERSITY 2 Acknowledgement To Get the Satisfied Dose Distribution • Some of materials provided by -Timothy Holmes- PhD : St Agnes Cancer Center, Baltimore MD -Thomas Rockwell Mackie – PhD : U of Wisconsin and TomoTherapy Inc. - Chester Ramsey-PhD : Thompson Cancer Center, Tenessee , USA 3 4 -Limited Number of Beams and Directions Cone Beam Non-uniform Intensities with the Conventional Linac plus MLC -Limited Number of Field Segmentations Limited Degree of Intensity Level 5 6 Siriraj Radiation Oncolgy
  • 2. Serial Tomotherapy : Peacock system Fan Beam Intensity TM Modulation • Common Name : Slice Therapy or Tomotherapy - Sequential /Serial Tomotherapy - Helical Tomotherapy 1994 Conventional Linear Accelerator added with Special MLC + Couch Control 7 8 Serious Problem in Serial Tomotherapy! Binary MLC MIMiC: NOMOS Maximum Field Size 2 x 20 OR 4 X 20 cm2 Indexing and couch immobilization device ( CRANE) Over or under dose 9 10 The New IMRT Delivery with Helical Tomotherapy ……. Couch Indexing Error of as little as 1 mm can increase the total non- uniformity to as much as 25% 11 Siriraj Radiation Oncolgy
  • 3. Concept for Helical Tomotherapy : Since 1993 CT ring gantry would be ideal for Tomotherapy with the modulated slit beam using the bank of fast moving collimators Spiral delivery should improve the hot-spot or cold spot problem Thomas Rockwell Mackie at the junction 13 14 Linac is mounted on a slip ring that allow Helical Tomotherapy is a Fusion of a continuous rotation around the patient (15-60 sec) Radiation Therapy Linear Accelerator and a Helical CT Scanner Independent Primary Jaws in the Superior- Inferior Direction 15 16 MLC TOMO Binary MLC Characteristic Optical sensors and pneumatic driven 17 18 Siriraj Radiation Oncolgy
  • 4. Increase Degree of Freedom Megavoltage CT Imaging Capability 51 projections/ revolution e ag Im o r CT tect e d Capability of obtaining a CT , before , after or even during the treatment will be possible 19 20 TOMO Beam Characteristic Lack of the Flattening Filter -No scatter caused outside the field - High dose rate Helical Tomotherapy Tomo Beam Characteristic Geometry Conical –shaped Profile Radial Profile 6 MV High Dose Source (860 MU/min, 1.5 mm point source) Low penumbra 3.5 MV Low Dose Source (20 MU/min, 1.5 mm point source) Lateral Profile 23 24 Siriraj Radiation Oncolgy
  • 5. Dose at Depth More Uniform MVCT Image Guidance 5 x5 cm Field Size 26 25 27 28 MVCT Imaging Quality High contrast resolution = 1.2-1.6 mm Low Contrast resolution = 2-4% 29 30 Siriraj Radiation Oncolgy
  • 6. Don’t Forget for the MVCT Number to Electron Density Conversion Table 31 32 Helical Tomotherapy Process TomoTherpy Process • Imaging / Contouring • Planning / Optimizing • In-room Megavoltage CT Imaging • Image Registration ( IGRT ) • Treatment Verification • Treatment Delivery 34 Optimization Create ROI Dose Delivery Capabilities Set initial value s for Importance Using maximum and Penalty U-shaped tumor likelihood Estimator Optimization Total 91,800 pencil beam were used in Spinal cord the optimization 35 Siriraj Radiation Oncolgy
  • 7. Planned Fluence Sinogram in Tomotherapy Leaf Control Planned Fluence Sinogram Sinogram Corrected From optimization process tongue & groove , 2D array of energy fluence that corrleate thread time between the projection and intensities 37 38 Plan QA 39 40 IGRT Total delivery time ≅ 30 minutes 41 42 Siriraj Radiation Oncolgy
  • 8. TomoTherapy vs. Clinical Application Only single , 6 MV Photon Beam ? No Electron Beam ? Questions Coplanar Only ? IMRT Only? Dosimetric/Clinical Advantage ? How about Integral Dose? 44 Dosimetric gain in CI and HI of PTV and sparing of OARs was significantly obtained in HT vs. Conventional IMRT But clinical advantage needs furthur investigation 45 46 HT prostate planning generally provided treatment plans with excellent target homogeneity and favorable critical structure sparing when compared to conventional IMRT 47 48 Siriraj Radiation Oncolgy
  • 9. Prostate , Vertebral –body retreatment = PTV Coverage + Sparing OAR , HT = Linac Pediatric ethmoid sacroma retreatment =PTV Coverage both OK , but HT show a little bit better sparing OAR Subtle dosimetric difference But no marked advantage with either system 49 50 SRS Capability 51 52 Helical Tomo shows larger lower isodose line volumes, longer treatment time , and can treat a much larger lesion than Gamma-knife 53 54 Siriraj Radiation Oncolgy
  • 10. 55 56 57 58 Dosimetric Advantage from Tomo but Integral Dose increase 6.5 % 59 60 Siriraj Radiation Oncolgy
  • 11. TomoTherapy Integral Dose!! A Potential Risk Factor for Secondary Cancer ? 61 Integral Dose = Mean Dose x Volume TOMO IMRT 6 MV 3DCRT 6 MV IMRT 63 64 AAPM 2007 Same protocol Adult prostate treatment Linac vs. Helical Tomo Pediatric CSI 65 66 Siriraj Radiation Oncolgy
  • 12. 67 68 TomoTherapy Some Concerned Issues 70 Longer Treatment Time!! 71 Siriraj Radiation Oncolgy
  • 13. Future of TomoTherapy Prepare for Adaptive RT 73 74 75 76 Thank You for Your Attention! Future Direction TomoDirect Discrete -angle delivery mode 77 78 Siriraj Radiation Oncolgy