4D Scan and Respiratory Gating
Download as PPTX, PDF43 likes10,412 views
The document outlines the principles and challenges of managing respiratory motion in radiotherapy, emphasizing the importance of accurately targeting tumors while minimizing exposure to healthy tissues. It discusses various strategies for tumor motion tracking and treatment planning, including motion encompassing methods, respiratory gating, and real-time tracking technologies. The evolving nature of Image Guided Radiation Therapy (IGRT) is highlighted as a promising solution for enhancing treatment precision and effectiveness.
4D Scan and Respiratory Gating
- 2. The goal of radiotherapy is to deliver a prescribed dose of radiation to the Target while sparing surrounding Healthy tissues to the largest extent possible Aim of Radiotherapy
- 3. How to achieve Correct tumour delineation Accurate planning Proper Delivery
- 4. Tumor Volume Delineation International Commission on Radiation Units and Measurements
- 5. ICRU 62: IM and ITV • Internal Margin (IM) Compensates for expected physiologic movements and variations in size, shape and position of the CTV in relation to an Internal Reference Point Commonly asymmetric May result from Respiration(Motion), different filling of Rectum/Bladder, Swallowing, Heart beat These variations cannot be easily controlled Internal Target Volume (ITV) = CTV + IM PTV = ITV + SM
- 6. Organ Motion Intra-fraction motion – during the fraction Heartbeat Swallowing Coughing Eye movement Inter-fraction motion - in between the fractions Tumour change Weight gain/loss Positioning deviation Breathing Bowel and rectal filling Bladder filling Muscle relaxation/tension
- 7. • All tumor motion is complex Tumor Cross-sectional View of Patient’s Chest Tumor Some motion is mostly Anterior / Posterior Some motion is mostly Superior / Inferior All tumor motion is Complex Organ motion during Respiration Ant Post
- 8. Reducing the CTV to PTV margin GTV CTV ITV PTV • Conventional: Increases dose to normal tissues, limiting factor for dose escalation • Accounting motion: CTV – PTV margin reduced
- 9. 4D Radiotherapy 9 Tumorshrinkage Tumor spread Weight loss Cardiac motion Hormone response Diet Intra-observer differences Respiratory motion
- 10. Respiratory motion affects: Respiratory motion affects all tumour sites in the thorax, abdomen and Pelvis. Tumours in the Lung, Liver, Pancreas, Oesophagus, Breast, Kidneys, prostate Tumour displacement varies depending on the site and organ Location Lung tumours can move several cm in any direction during irradiation It is most prevalent and prominent in Lung cancers
- 11. Problems associated with respiratory motion during RT Image acquisition limitations Treatment planning limitations Radiation delivery limitations
- 12. Image Acquisition Limitations Motion artifacts result if respiratory motion not accounted for This can result in target/normal tissue delineation errors Distorted images, incorrect anatomical positions, volumes or shapes Conventional With gated imaging Tumor
- 13. Treatment Planning Limitations Larger margins have to be used when creating PTV from CTV Increased margins mean greater volumes of healthy tissue treated CTV CTV PTV PTV Motion taken into accountConventional
- 14. Radiation Delivery Limitations Intrafraction motion produces averaging/blurring of dose distribution over path of motion Interfraction motion produces shift of dose distribution Overall effect is blurring of the dose distribution near the beam edges
- 15. • Respiratory motion management If target motion >5 mm – RMM technology is appropriate also appropriate when the procedure will increase normal tissue sparing A clinical process guide for managing respiratory motion
- 16. Various Types of Tracking Respiration R P M C A L Y P S O A N Z A I S P I R O M E T E R ABC
- 17. Tracking Respiration – VARiAN RPM • External Marker RPM (Real time Position Management ) by Varian Reflective markers “learn” the patient’s breathing pattern Camera system Sends signal Reflected off markers Respiratory waveform created Shape represents tumor movement
- 18. Tracking Respiration Internal Markers – Implanted gold seeds – Use flouroscopy to locate
- 20. Methods to Account for Respiratory Motion 1. Motion encompassing methods 2. Respiratory gating methods 3. Breath hold methods 4. Forced shallow breathing with abdominal compression 5. Real-time tumor tracking methods
- 21. 1. Motion encompassing methods Technique that include entire range of tumor motion Slow CT Inhalation and exhalation breath-hold CT Four-dimensional 4D or respiration-correlated CT
- 22. Slow CT scanning Acquire CT images at single couch position during a respiratory cycle (slightly longer) -Record amplitude and phase for each slice Move the couch the distance of the detector width and obtain CT images for respiratory cycle Fuse images based on phase of respiratory cycle Generate 4D images Disadvantage – Loss of resolution due to motion blurring (larger errors in tumor and normal tissue delineation)
- 23. Motion encompassing methods: 4DCT
- 24. Inhalation and exhalation breath - hold CT • Acquire both inhalation and exhalation gated or breath-hold CT scans • Relies on the patient’s ability to hold his or her breath reproducibly. • Require image fusion and extra contouring. • For lung tumors, Maximum Intensity Projection (MIP) tool can be used to obtain the tumor-motion encompassing volume, • Advantage over slow scanning method – Blurring caused by the motion present during Free Breathing is significantly reduced
- 25. 5 different phases MIP =
- 26. 4D-CT / Respiration-correlated CT • Determines the mean tumor position, tumor range of motion for treatment planning • Can be used to reconstruct inhalation, exhalation, and slow CT Scans • The MIP tool can be used for obtaining the tumor-motion- encompassing target volume • Another motion-encompassing method is to derive a single set out of the 4D CT scan where the tumor is close to its time-averaged position. In that case, the expected dose blurring effect of respiration can be accounted for in the CTV-PTV margin
- 27. 2. Respiratory Gating Methods Displacement gating (Amplitude) Phase gating
- 28. Respiratory gating methods Involves the administration of radiation during both imaging and treatment delivery within a particular portion of the patient’s breathing cycle, commonly referred to as the “gate” Displacement Gating (Amplitude) – relative position between two extremes of breathing motion, namely, inhalation and exhalation. – the radiation beam is activated whenever the respiration signal is within a pre-set window of relative positions. Phase Gating – respiration signal that must satisfy periodicity criteria – the radiation beam is activated when the phase of the respiration signal is within a pre-set phase window.
- 29. Breathe Out Breathe In Amplitude Gating Example Beam On! Beam Hold! Beam Hold! Beam On! Beam On! Upper threshold Lower threshold Full Expiration Full Inspiration
- 30. Breathe Out Breathe In Phase Gating Example Beam On! Beam Hold! Beam Hold! Beam On! Beam On! On Off On Off On Off
- 31. Respiratory gating methods 4D CT Data Acquisition RetrospectiveProspective
- 32. Breathing Cycle Full Inspiration 0% 50% Full expiration 25%75%
- 33. 4D CT Data Acquisition - Prospective CT Scan Axial scan trigger, 1st couch position Axial scan trigger, 2nd couch position Exhalation Inhalation Scan Scan Scan Axial scan trigger, 3rd couch position Images are acquired only during a portion of the respiration cycle
- 34. 4D CT Data Acquisition -Retrospective Images are acquired during the entire respiration cycle and sorted later X-ray on Exhalation Inhalation 1st couch position 2nd couch position 3rd couch position “Image acquired” signal to RPM system (Ford 2003, Vedam 2003)
- 35. • Deep - Inspiration Breath Hold (DIBH) • Active-breathing control (ABC) • Self-held breath hold without respiratory monitoring 3. Breath-hold methods
- 36. Deep-Inspiration Breath Hold Patient is trained to reproduce a deep inhalation breath hold during simulation and treatment Volume of air inhaled by patient monitored by spirometer Highly reproducible results possible
- 37. Active-Breathing Control Technique for suspending breathing at any predetermined position (usually moderate or deep inhalation) Monitoring apparatus consists of Spirometer connected to balloon valve After a pre-defined volume of air (threshold volume) has passed through the spirometer spirometer, a small balloon valve, inflates and occludes the tube, applying an assisted breath hold for a predefined period of time
- 38. Active Breathing Co-ordinator Spirometer Breath Hold Pattern
- 39. • Originally developed for stereotactic irradiation of small lung and liver lesions • The patient is immobilized and positioned using the stereotactic body frame SBF, consisting of a rigid frame with an attached “vacuum pillow” that is custom fitted to each patient. 4. Forced shallow breathing with abdominal compression
- 40. 5. Real-time tracking methods Fluoroscopy based tracking Systems Fiducial Markers Implanted Systems (Gold Seeds) Electromagnetic Field Tracking Systems
- 41. Real-time tumor-tracking methods - Fluoroscopy based tracking Systems • To detect respiratory motion using radiation beam follow the tumours changing position • Difficulty of detecting the tumour itself, Surrogate markers are used in most cases
- 42. Real-time tumor-tracking methods - Fiducial Markers Implanted Systems Internal markers • Direct visualization of tumor (surroundings) • Invasive procedure / side effects of surgery External markers • Limited burden for patient • Doubtful correlation between marker and tumor position • Intra-fractional • Inter-fractional + - - +
- 43. Real-time tumor-tracking methods - Electromagnetic Field Tracking Systems • Calypso® Extracranial Tracking Step 1 Step 2 Electromagnetic Locate and Track Continuously Electromagnetic array sends pulses of electromagnetic energy to beacons Beacons return electromagnetic signal to the array
- 45. Quality Assurance (During Commissioning) RPM mini-phantom in conjunction with the marker block is used to test the RPM system’s tracking ability in both the CT room and the treatment room prior to any respiratory gating procedure Breathing Mini-Phantom Six dot marker block Breathing Pattern
- 46. CIRS – Dynamic Phantom Point Dose Measurement
- 47. 4D Radiotherapy 4D CT Imaging 4D Treatment Planning 4D Treatment Delivery Acquisition of a sequence of CT image sets over consecutive phases of a breathing cycle The explicit inclusion of the temporal changes in anatomy during the imaging, planning and delivery of radiotherapy Designing treatment plans on CT image sets obtained for each phase of the breathing cycle Continuous delivery of the 4D treatment plans throughout the breathing cycle The 4D radiotherapy process
- 48. Recommended clinical process for respiratory motion during the radiotherapy • Recommended 5 mm motion-limit criterion value may be reduced for special procedures, such as SBRT • May be reduced in the future as other errors in radiotherapy, such as target delineation and setup error, are reduced, with respiratory motion thereby becoming the accuracy limiting factor. • Exhale position most reproducible • Inhale position most beneficial for sparing lung tissue AAPM Task Group 76
- 49. Conclusion The management of respiratory motion in radiation oncology is an evolving field IGRT provides a solution for combating organ motion in radiotherapy Delivering higher dose to tumor and less dose to normal tissue. Limited clinical studies, needs to be studied further IGRT – the future of radiotherapy