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Igrt And Resp Gating Final Version

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IGRT and Respiratory Gating

IGRT and Respiratory Gating


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  • 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. Outline
    • Basic Principles of Image Guided Radiation Therapy (IGRT) and Respiratory Gating (RG)
    • Workflow: IGRT
      • Image acquisition
      • Positioning accuracy and image quality
      • Potential use for Image Guided Radiation Therapy through selected clinical examples
  • 3. Outline
    • Different types of CBCT – Vendor specific approaches
    • Workflow: Respiratory Gating
      • Establishing good sinus pattern acquisition
      • Establishing the treatment “Gates”
      • Monitoring patient respiratory rhythm during treatment
  • 4. Objectives
    • The participants will understand the current practice of IGRT and DGRT as it related to CBCT
    • The participants will be aware of future trends of CBCT
    • Understanding of the importance of Respiratory Gating and it’s relationship with IGRT
    • Understanding the basic principles of respiratory pattern and treatment “gates”
  • 5. IGRT- Working Definition
    • Treatment systems with integrated imaging capability enabling a highly accurate patient set-up, compensating for any interfraction motion
    “ Old Days” IMRT, SBRT,.. “ Now-A Days”
  • 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. Choice Of IGRT
    • Helical MVCT 6 YES NO Pretty good
    “ The data showed a sharper peak and a narrower spread of values for AlignRT than for OBI”
    • CBCT(kV) 6 YES NO YES
    • Optical Tracking 6 NO YES NO
    • CBCT(MV) 6 YES NO Not great
    • RF Tracking 6? Surrogate YES NO
    • “ Choose Your Poison”
    • Technique DOF Internal Anatomy RealTime Soft Tissue
    • Port Film 3 NO NO NO
    • Novel-MRI 6 YES YES? YES
    The best choice might be a “hybrid” or combination of imaging technologies. ASTRO 2007 (abstract 43).
  • 8. IGRT- Is It Really Necessary? We are not dealing with a static image!
  • 9. Cone Beam CT
    • Conventional CT
      • ‘ Fan’ beam
      • 1D detector
      • 1 rotation = 1 slice
    • Cone Beam CT
      • ‘ Cone’ beam
      • 2D detector
      • 1 rotation = volume (many slices)
    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. Cone Beam CT
    • Available Cone Beam Systems
    Elekta Synergy™ Siemens Artiste™ Varian Trilogy™ Bench Top C-Arms
  • 11. Cone Beam CT CBCT versus Fan Beam CT
  • 12. Cone Beam CT Moving Gas
  • 13. Cone Beam CT Motion Artifact
  • 14. IGRT- Why Do We Need It?
  • 15. IGRT- Why Do We Need It?
  • 16. IGRT- What Does It Take?
    • Patient set-up- Nothing new here
    • Acquire CBCT Image
    • 3D Image Reconstruction- 200 projections
    • Image Fusion- CBCT and Planning CT
    • Visual validation of match- What can go wrong?
    UCSF CRAZY Shifts!
    • Re-position patient using Table shifts & Tx!
  • 17. IGRT- High Z Artifacts UCSF kV MV
  • 18. IGRT- Respiratory Motion The perfect transition since we now know the importance of IGRT, let’s now consider Respiratory Gating and 4D!
  • 19. Step 1- 4D Acquisition Impact of Breathing-Related Motion on CT AAPM TG76 Report (Keall et al)
  • 20. Comparison of ungated and gated case
  • 21. 4D Acquisition
    • Siemens Uses Anzai Belt With Transducers
    • Belt is placed around patient
    • The transducers is held in place by belt
    • The transducer signal is interfaced to CT scanner to provide the Respiratory Cycle
    • This correspondence allows each slice to be “tagged” with the breathing cyle. (“4th” –D)
  • 22. Data “Mining”
    • Respiration is monitored by system. Patient does not need to maintain a constant breathing pattern.
    • Software categorize the breathing cycle into “BINS” which are decided by user.
      • For example 0%-25%-50%-75%-100% IN and EX
        • Or 0%-20%-40%-60%-80%-100% IN and EX
    • The operator decides the number of BINS for reconstruction
  • 23. 4D Reconstruction
    • All of the determined “BINS” of data are reconstructed to produce a 4 Dimensional image of the Breathing patient
  • 24. 4D Visualization
    • The 4 Dimensional patient is viewed by the Physician, Physicist/Dosimetrist prior to export to the RTP system.
  • 25.  
  • 26.  
  • 27. 4D Treatment Planning
    • Disclaimer: I am by no means an “expert” on this topic. I will share with you what I know today
    • 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
  • 28. 4D Treatment Planning
    • Now to contour on ALL the BIN’s of data (>1,000 slices!)
    • “ Houstin, we need more time!”
  • 29.  
  • 30. 4D Treatment Planning- “Poor Man’”
  • 31.  
  • 32. 4D Treatment Planning
    • Some of these new tools can “propagate” what is contoured on ONE data set (BIN) to all the remaining 900+ slices!
    • The result is the creation of an “ITV” or Internal Target Volume which encompasses the GTV on ALL the 4D data-sets.
    • However, this approach comes with the “cost” of treating more normal lung.
    • 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!
  • 33.  
  • 34. Respiratory Gated Delivery
    • This is the final step from 4DCT Simulation  4D Treatment Planning  GATED Delivery
    • The patient is set-up with the same Respiratory monitoring equipment used during the 4D Simulation
    • Next, the Respiratory signal is optimized and the treatment “GATES” are set to coincide with the 4D Planning data
    • The patient has the “routine” IGRT session followed by the GATED Treatment Delivery
  • 35.  
  • 36. Pretty good example
  • 37. Pretty “bad” example
  • 38. Moral To The Story
    • Not ALL patients have a consistent breathing pattern. Some are good, others NOT
    • This doesn’t necessarily mean you cannot use Respiratory Gating for the treatment delivery
    • However you should ask yourself “is it worth it?”
    • Using Gating for delivery will increase the total delivery time by a factor of FOUR
    • If you are performing SBRT, that is a very long treatment delivery!
  • 39. IGRT and Respiratory Gating
    • We have see the benefits of IGRT on set-up accuracy
    • We have “seen” the effect of breathing motion and we can no longer afford to use static CT data, especially for SBRT!
    • If we can image the patient (IGRT) AND Gate the delivery (Resp. Gating), this will enable us to:
      • Dose Escalate and Hypo fractionate
  • 40. Thank You for your time !