Igrt And Resp Gating Final Version
- 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.
- 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!”
- 30. 4D Treatment Planning- “Poor Man’”
- 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!
- 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
- 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 !