Igrt And Resp Gating Final Version

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IGRT and Respiratory Gating

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Igrt And Resp Gating Final Version

  1. 1. IGRT and Respiratory Gating: Can We See It and Can We Hit It? Joe L. Meadows, M.S. Medical Physicist The Lacks Cancer Center Saint Mary’s Health Care Grand Rapids, MI
  2. 2. Outline <ul><li>Basic Principles of Image Guided Radiation Therapy (IGRT) and Respiratory Gating (RG) </li></ul><ul><li>Workflow: IGRT </li></ul><ul><ul><li>Image acquisition </li></ul></ul><ul><ul><li>Positioning accuracy and image quality </li></ul></ul><ul><ul><li>Potential use for Image Guided Radiation Therapy through selected clinical examples </li></ul></ul>
  3. 3. Outline <ul><li>Different types of CBCT – Vendor specific approaches </li></ul><ul><li>Workflow: Respiratory Gating </li></ul><ul><ul><li>Establishing good sinus pattern acquisition </li></ul></ul><ul><ul><li>Establishing the treatment “Gates” </li></ul></ul><ul><ul><li>Monitoring patient respiratory rhythm during treatment </li></ul></ul>
  4. 4. Objectives <ul><li>The participants will understand the current practice of IGRT and DGRT as it related to CBCT </li></ul><ul><li>The participants will be aware of future trends of CBCT </li></ul><ul><li>Understanding of the importance of Respiratory Gating and it’s relationship with IGRT </li></ul><ul><li>Understanding the basic principles of respiratory pattern and treatment “gates” </li></ul>
  5. 5. IGRT- Working Definition <ul><li>Treatment systems with integrated imaging capability enabling a highly accurate patient set-up, compensating for any interfraction motion </li></ul>“ Old Days” IMRT, SBRT,.. “ Now-A Days”
  6. 6. OPTICAL TRACKING TECHNOLOGY Over the past 20-30 years our ability to “visualize” what we are treating (beyond skin marks) has dramatically changed! IGRT- Working Definition Prostate US H&N EPID http://biomedcentral.inist kV cone beam CT (CBCT) University of Heidelberg radonc.ucsf.edu Medical Dosimetry, Vol. 32, No. 2, pp. 111-120, 2007 Calypso employs radiofrequency technology comparable to the global positioning system to continuously and precisely monitor biologically inert transponders implanted in the prostate. When prostate displacement exceeds predetermined thresholds, (i.e., 5 mm for more than 10 seconds) treatment can be halted temporarily to readjust the patient's position. Calypso® System Tracking and Target Localization during Radiotherapy for Prostate Cancer https://www.virginiamason.org Odd couple: A prototype device combines a magnetic resonance imager with a linear accelerator. The blue cylinders facing each other are the imaging magnets. The metal circle visible to the left at the back is a magnetic and radiation shield that protects the accelerator’s waveguide. Credit: University of Alberta Cross Cancer Institute Acquire five two-dimensional MRI images per second using Compressive Sensing , acquire only the most important 10 percent of the image data in the first place- FAST!
  7. 7. Choice Of IGRT <ul><li>Helical MVCT 6 YES NO Pretty good </li></ul>“ The data showed a sharper peak and a narrower spread of values for AlignRT than for OBI” <ul><li>CBCT(kV) 6 YES NO YES </li></ul><ul><li>Optical Tracking 6 NO YES NO </li></ul><ul><li>CBCT(MV) 6 YES NO Not great </li></ul><ul><li>RF Tracking 6? Surrogate YES NO </li></ul><ul><li>“ Choose Your Poison” </li></ul><ul><li>Technique DOF Internal Anatomy RealTime Soft Tissue </li></ul><ul><li>Port Film 3 NO NO NO </li></ul><ul><li>Novel-MRI 6 YES YES? YES </li></ul>The best choice might be a “hybrid” or combination of imaging technologies. ASTRO 2007 (abstract 43).
  8. 8. IGRT- Is It Really Necessary? We are not dealing with a static image!
  9. 9. Cone Beam CT <ul><li>Conventional CT </li></ul><ul><ul><li>‘ Fan’ beam </li></ul></ul><ul><ul><li>1D detector </li></ul></ul><ul><ul><li>1 rotation = 1 slice </li></ul></ul><ul><li>Cone Beam CT </li></ul><ul><ul><li>‘ Cone’ beam </li></ul></ul><ul><ul><li>2D detector </li></ul></ul><ul><ul><li>1 rotation = volume (many slices) </li></ul></ul>CBCT is based on the same principle as conventional fan beam CT, except that an entire volumetric dataset can be obtained through a single rotation of the source and detector. This is made possible by the use of a 2-D detector, as opposed to the one-dimensional (1-D) detectors used in conventional CT.
  10. 10. Cone Beam CT <ul><li>Available Cone Beam Systems </li></ul>Elekta Synergy™ Siemens Artiste™ Varian Trilogy™ Bench Top C-Arms
  11. 11. Cone Beam CT CBCT versus Fan Beam CT
  12. 12. Cone Beam CT Moving Gas
  13. 13. Cone Beam CT Motion Artifact
  14. 14. IGRT- Why Do We Need It?
  15. 15. IGRT- Why Do We Need It?
  16. 16. IGRT- What Does It Take? <ul><li>Patient set-up- Nothing new here </li></ul><ul><li>Acquire CBCT Image </li></ul><ul><li>3D Image Reconstruction- 200 projections </li></ul><ul><li>Image Fusion- CBCT and Planning CT </li></ul><ul><li>Visual validation of match- What can go wrong? </li></ul>UCSF CRAZY Shifts! <ul><li>Re-position patient using Table shifts & Tx! </li></ul>
  17. 17. IGRT- High Z Artifacts UCSF kV MV
  18. 18. IGRT- Respiratory Motion The perfect transition since we now know the importance of IGRT, let’s now consider Respiratory Gating and 4D!
  19. 19. Step 1- 4D Acquisition Impact of Breathing-Related Motion on CT AAPM TG76 Report (Keall et al)
  20. 20. Comparison of ungated and gated case
  21. 21. 4D Acquisition <ul><li>Siemens Uses Anzai Belt With Transducers </li></ul><ul><li>Belt is placed around patient </li></ul><ul><li>The transducers is held in place by belt </li></ul><ul><li>The transducer signal is interfaced to CT scanner to provide the Respiratory Cycle </li></ul><ul><li>This correspondence allows each slice to be “tagged” with the breathing cyle. (“4th” –D) </li></ul>
  22. 22. Data “Mining” <ul><li>Respiration is monitored by system. Patient does not need to maintain a constant breathing pattern. </li></ul><ul><li>Software categorize the breathing cycle into “BINS” which are decided by user. </li></ul><ul><ul><li>For example 0%-25%-50%-75%-100% IN and EX </li></ul></ul><ul><ul><ul><li>Or 0%-20%-40%-60%-80%-100% IN and EX </li></ul></ul></ul><ul><li>The operator decides the number of BINS for reconstruction </li></ul>
  23. 23. 4D Reconstruction <ul><li>All of the determined “BINS” of data are reconstructed to produce a 4 Dimensional image of the Breathing patient </li></ul>
  24. 24. 4D Visualization <ul><li>The 4 Dimensional patient is viewed by the Physician, Physicist/Dosimetrist prior to export to the RTP system. </li></ul>
  25. 27. 4D Treatment Planning <ul><li>Disclaimer: I am by no means an “expert” on this topic. I will share with you what I know today </li></ul><ul><li>This step involves using the 1,000 or more images to characterize the motion of the target and normal anatomy in designing the treatment fields </li></ul>
  26. 28. 4D Treatment Planning <ul><li>Now to contour on ALL the BIN’s of data (>1,000 slices!) </li></ul><ul><li>“ Houstin, we need more time!” </li></ul>
  27. 30. 4D Treatment Planning- “Poor Man’”
  28. 32. 4D Treatment Planning <ul><li>Some of these new tools can “propagate” what is contoured on ONE data set (BIN) to all the remaining 900+ slices! </li></ul><ul><li>The result is the creation of an “ITV” or Internal Target Volume which encompasses the GTV on ALL the 4D data-sets. </li></ul><ul><li>However, this approach comes with the “cost” of treating more normal lung. </li></ul><ul><li>To spare more normal lung you could propagate the GTV only to the BIN’s or portions of the Respiratory Cycle that will be used to TREAT the patient = GATED DELIVERY! </li></ul>
  29. 34. Respiratory Gated Delivery <ul><li>This is the final step from 4DCT Simulation  4D Treatment Planning  GATED Delivery </li></ul><ul><li>The patient is set-up with the same Respiratory monitoring equipment used during the 4D Simulation </li></ul><ul><li>Next, the Respiratory signal is optimized and the treatment “GATES” are set to coincide with the 4D Planning data </li></ul><ul><li>The patient has the “routine” IGRT session followed by the GATED Treatment Delivery </li></ul>
  30. 36. Pretty good example
  31. 37. Pretty “bad” example
  32. 38. Moral To The Story <ul><li>Not ALL patients have a consistent breathing pattern. Some are good, others NOT </li></ul><ul><li>This doesn’t necessarily mean you cannot use Respiratory Gating for the treatment delivery </li></ul><ul><li>However you should ask yourself “is it worth it?” </li></ul><ul><li>Using Gating for delivery will increase the total delivery time by a factor of FOUR </li></ul><ul><li>If you are performing SBRT, that is a very long treatment delivery! </li></ul>
  33. 39. IGRT and Respiratory Gating <ul><li>We have see the benefits of IGRT on set-up accuracy </li></ul><ul><li>We have “seen” the effect of breathing motion and we can no longer afford to use static CT data, especially for SBRT! </li></ul><ul><li>If we can image the patient (IGRT) AND Gate the delivery (Resp. Gating), this will enable us to: </li></ul><ul><ul><li>Dose Escalate and Hypo fractionate </li></ul></ul>
  34. 40. Thank You for your time !

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