Evaluation and imaging for lung SBRT
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The document discusses the key steps in pre-SBRT workup including medical evaluation, tumor assessment, imaging, and motion management. It notes that patients with stage I lung cancer can be treated with surgery, sublobar resection, or SBRT depending on their risk level. For medically inoperable patients, imaging includes PET/CT and pathology confirmation if possible. Pulmonary function tests and cardiac evaluation are done. Tumor characteristics like size and location are assessed. During simulation, immobilization and respiratory motion management techniques like 4DCT are used to accurately define the tumor and organs at risk.
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Evaluation and imaging for lung SBRT
- 1. Pre SBRT workup, Imaging and Contouring Dr. Naveen Mummudi, Dr. J P Agarwal IAEA-RTC meet – May 2017
- 2. MDT discussion Pre-SBRT work up Simulation Tumour and OAR contouring Treatment planning and plan evaluation Treatment delivery Follow up for toxicity
- 3. MDT / clinical forum
- 4. MDT / clinical forum • Patients with stage I lung cancer are candidates for curative treatment and can be divided into three major groups: • Low-risk surgical patients - usually treated by lobectomy; • High-risk surgical patients - treated with sublobar (segmental or wedge) resection or SBRT; and • Medically inoperable patients - treated with EBRT or SBRT
- 5. MDT / clinical forum • Inoperable • Majority • Operable • Patient preference • Clinical trial setting Medical inoperability Defined as “the presence of co-morbid illnesses that renders the patient at higher than acceptable risk of surgical morbidity and mortality.” Competing risk scenario - where risk of death from medical illnesses is balanced by the risk of death from lung cancer. Colice, Shafazand et al. 2007
- 6. Pre SBRT work up • Metastatic workup • Diagnosis – Pathological / Radiological • Imaging – CT / PET CT / MR Brain • Medical condition assessment • Pulmonary reserve • Cardiology status • Other comorbid conditions • Tumour characteristics • Location – Peripheral / central / ultra central
- 7. Oncological assessment • Imaging • PET CT whole body / CECT Thorax • MRI brain • EUS-TBNA: ?role • 2 prospective trials evaluating PET+/- EUS-TBNA • Confirmation of diagnosis • Pathological – CT guided/trans-bronchial • Radiological – imaging characteristics
- 9. Oncological assessment …developed a model that demonstrates that treating an SPN without pathology is justified when the likelihood of malignancy is 85% Louie 2014
- 10. Medical assessment • Pulmonary function • GOLD – COPD • ACCP recommendations • Cardiac evaluation • Charlson comorbidity index
- 11. Lung volumes - Spirometry
- 12. Spirometry • Patients with advanced lung disease have decreased survival defined by the severity of their disease. • In patients with COPD, FEV 1 < 35% predicts approximately 10% mortality per year (50% 5-year survival).
- 13. Medical evaluation • DLCO • Cardiopulmonary Exercise Testing • 6 minute walk test / Incremental shuttle walk test • Split function test • Ventilation/perfusion scinitigraphy • Cardiac evaluation • 2D ECHO
- 14. Algorithm for cardiac assessment ERS/ESTS task force 2009
- 15. ERS/ESTS task force 2009
- 17. Tumour characteristics • Size • Location of tumour • Severe toxicity rates of 17% and 46% at 3 years for peripheral and central lesions Timmerman, 2003, Chest McGarry, 2005, IJROBP Glide-Hurst, 2014, J thorac dis
- 18. Tumour characteristics Roesch, RO, 2016
- 22. Immobilization • Accurately re-position patient • Reduce/Minimize patient voluntary and involuntary motion • Reduce/Minimize organ/target motion • Abdominal compression • Comfortable for long treatment • Compatible with IGRT • Not interfere with treatment beam Body Pro-Lok TM frame Body Fix Abdominal Compression Thermoplastic Long mask
- 23. Commercial devices Abdominal compression belt • Plastic board with two long slits on the sides • Blood pressure cuff, Velcro® mounted under the board • Adjustable, Velcro® covered belt • Sewn-on ruler for consistent setup Pneumatic Compression Belt • Air inflation bulb • Pressure gauge • Non-Rigid • Marking of the patient skin & immobilization device • Recording of the pressure
- 24. Immobilization/Simulation • Careful positioning in the immobilization device, supporting the hands and shoulders • premedication with analgesia (e.g., to prevent shoulder pain) • anxiolytic may be needed • Scanning in TX Position • CT, MR, PET-CT • CT scan with ≤ 3 mm slice thickness • Motion Management • Abdominal Compression Plate • Pressure Belt • Body Immobilization
- 25. Respiratory motion Causes artifacts during imaging acquisitions Radiation delivery limitations Limiting treatment planning Treatment planning difficulty
- 26. When to manage respiratory motion? AAPM Task Group 76: respiratory management techniques should be considered if either of the following conditions occur – • > 5 mm range of motion is observed in any direction • Significant normal tissue sparing can be gained using respiration management 26 The Management of Respiratory Motion in Radiation Oncology; Report of AAPM Task Group 76 July 2006 by American Association of Physicists in Medicine
- 27. Recommended Clinical Process for patients with whom respiratory motion during RT is a concern 27
- 28. Methods to Account for Motion • Motion-encompassing methods • Respiratory gating methods • Breath-hold methods • Forced shallow breathing with abdominal compression • Real-time tumor-tracking methods
- 29. CT Simulation • Suppressed respiratory motion techniques • Compression Paddle, Pressure Belt • Free Breathing (FB) & Slow CT-Scanners • Free Breathing & Fast CT-Scanners • Breath-Hold (BH) CT-Scans • Respiratory Correlated CT (4D-CT)
- 30. Motion Management Strategies Method Technique Incorporate all movements 4DCT or Slow CT Freeze movement Breath hold Intercept movement Gated Radiotherapy Track or Chase the tumor Implanted markers and specialized treatment delivery 30
- 31. Slow CT scanning • Scanner operates at a particular couch position for longer than the respiratory cycle so that the image of the tumor would show the full extent of respiratory motion. • Yields a tumor-encompassing volume • Limitation: respiratory motion will change between imaging and treatment; • additional margins are required to account for these variations. • One CT scan is obtained • overall treatment process does not increase in complexity over that of a free-breathing CT scan • Loss of resolution due to motion blurring, which potentially leads to larger observer errors in tumor and OAR delineation. • only recommended for lung tumors that are not involved with either the mediastinum or the chest wall. • Increased dose of radiation from slow CT scanning compared with conventional CT scanning. 31
- 32. Inhale and exhale breath-hold CT • Advantage: blurring caused by motion present during free breathing is significantly reduced during breath-hold. • But taking both inhale and exhale CT scans will increase scanning time and relies on the patient’s ability to hold breath reproducibly. • Two scans will be obtained; thus, image fusion and extra contouring are required. • Dose calculation should be performed on the CT data set that is most appropriate for the particular patient, e.g., exhale CT for patients generally spending more time at exhale than inhale. • The exhale scan will tend to underestimate the lung volumes and, hence, overestimate the percentage of lung volume receiving a specific dose. 32
- 33. Respiratory-triggered CT scan • Slice acquisition is triggered by a respiratory signal, such that slices are only acquired in a pre-set phase of respiratory cycle. • The result is a 3D image in which all the slices are acquired in the same phase of breathing. • A scan is acquired with the imaging beam on during the entire breathing cycle and this is performed at all couch positions. Subsequently CT slices are reconstructed at consecutive points of the breathing cycle. 33 4-D CT
- 34. Patient Training • The ability to achieve reproducible breathing or breath-hold patterns is a requirement for allowing the patient to proceed to simulation and treatment. • Prior to the start of simulation, the patient should be made familiar with the equipment and its purpose. • A physicist or trained designee should perform the coaching and evaluation, at least in the initial clinical implementation. 34
- 35. Different ways to acquire respiratory trace • VARIAN : Real-Time Position Management System (RPM) 35 • ELEKTA : Active Breath Coordinator (ABC) • SIEMENS : ANZAI belt
- 36. RPM system • Consists of a plastic marker block with six metallic reflectors (3 cm apart for calibrating amplitude) which is placed on patient’s abdomen between the xiphoid and umbilicus. • A infrared camera records the abdominal surface motion. • RPM software tracks the marker trajectory in real time and calculates the respiratory phase on the basis of observed amplitude. • CT scanner and RPM system communicate during data acquisition to indicate when beam is turned on or off. 36
- 37. Marker Block RPM system can detect the motion of the marker block in vertical, lateral and longitudinal dimensions. 37
- 38. 4DCT • 4DCT scans can be performed both in sequential and in helical scanning modes — • In sequential mode, beam is kept on during a breathing cycle at each couch position • In helical mode, beam is kept on during the entire scan, while the pitch is very low. • In both cases, this in effect provides a densely oversampled scan. 38
- 39. 39
- 40. 40
- 41. 4DCT • Typically, a total of 1000 –1500 images are acquired during a 4D-CT study. Approximately 20 –25 images are reconstructed per slice, evenly distributed throughout the respiratory period. • Each reconstructed axial image represents the anatomy at a different instant during the patient’s respiratory cycle. • On the basis of the temporal correlation between the surface motion and image data acquisition, a specific respiratory phase is assigned to each image. • An axial image at a given couch position is binned on the basis of its respiratory phase. 41
- 42. 42
- 43. Phase vs. Amplitude sorting • Majority of the published 4D-C T techniques have used a time-based phase sorting method for retrospectively gating image data. • This is subject to misalignment due to varying inhale and exhale slopes, periods, and amplitudes in the respiration trace. • Rietzel et al. proposed an amplitude sorting method -- a constant amplitude on the respiratory curve is chosen to designate the phase position. • Although this method eliminates the possibility of misalignment, it increases the potential for missing phase sets. If a certain amplitude is not reached in all cycles of the recorded respiration trace, then that phase set cannot be created without a gap in the volume. 43 Rietzel E, Pan TS, C hen GTY. 4D CT: Image formation and clinical protocol. Med Phys. 2005;32(4):874-889
- 44. 4DCT • 4D CT scan not only reduces motion artifacts, but also gives the tumor/organ motion information. • There may still be blurring artifacts in each slice caused by the residual motion within the slice acquisition time, but shorter the slice acquisition time, smaller the artifacts. • 4D CT scan is NOT really 4D Temporal information is mapped onto one breathing cycle. Irregular respiration will cause artifacts in 4D CT images. Breath coaching is always needed. 44
- 45. 4DCT • 4DCT scanning procedure of the entire thorax takes about 90 s. • Radiation exposure from 4DCT acquisition is approximately six times the dose of a single conventional helical CT scan (range 0.02 - 0.09 Gy) • Generation of individualized and usually smaller target volumes derived from 4DCT scans in comparison to standard PTVs justifies this additional radiation exposure 45
- 46. 46
- 47. H. Hof et al. / Radiotherapy and Oncology 93 (2009) 419–423 Conventional vs. 4D based target definition PTV4D is not only smaller in most parts but also extends to areas not covered by PTVconv 47
- 48. Using 4DCT data to draw Target • A composite target volume is the union of individual target volumes at different instants in time. • The standard approach would include contouring GTVs on all binned data sets (usually 10). • Alternatively, contour GTV on the volumes at end-inhale and end-exhale and fuse them. The composite contours from these extreme data sets are then overlaid onto each breathing phase and visually verify whether the composite volume includes all instances of GTVs at other respiratory phases. • Strategy of contouring extreme tumor positions will fail whenever the size of the tumor is smaller than its motion amplitude. 48
- 49. 4-D CT: Generating Target Volumes 49 Different Target Volumes derived from GTV Target definition according to the recommendations in ICRU Report 62 ICRU Report 62 recommends use of an internal target volume (ITV) to account for variations in size, shape, and position of the CTV International Commission on Radiation Units and Measurements. ICRU report 62: Prescribing, recording, and reporting photon beam therapy (Supplement to ICRU report 50). Bethesda, MD: ICRU 1999
- 50. Maximal Intensity Projection (MIP) • When a significant density difference exists between the tumor and surrounding tissue, it may be exploited to decrease the contouring workload. • A Maximal Intensity Projection (MIP) is automatically generated from the entire 4D-CT by assigning each voxel the greatest Hounsfield unit value from all corresponding voxels over the multiple respiratory phase image data. • For a lung tumor, this results in identification and localization of high- density tumor voxels compared with lower density lung tissue voxels. 50
- 51. Failure of MIP technique 51 Rietzel et al. Maximum-intensity volumes for fast contouring of lung tumors Including respiratory motion in 4dct planning; Int. J. Radiation Oncology Biol. Phys., Vol. 71, No. 4, pp. 1245–1252, 2008 While contouring using MIP technique one needs to be careful for nodal volumes within the hilum or mediastinum, tumors located near the diaphragm, and tumors surrounded by atelectasis
- 52. Window effect For Parenchymal disease: W=1600 L= -600 For Mediastinal disease: W=400 L=20 These correlate best with pathological tumor sizes
- 53. Tumor and OAR Delineation • If 4DCT unavailable or unsuitable free-breathing helical images can be used for treatment planning • In selected patients intravenous CT contrast may help to identify the GTV • When PET imaging is available (either in the diagnostic or preferably, the treatment position) it is fused to the exhale CT and may be used to inform the contouring process, especially in instances where there is a neighbouring region of atelectasis Planning Target Volume (PTV) • For the remaining uncertainty a setup margin is required • A uniform expansion of 5 mm is typically applied to the 4DCT based ITV to generate the PTV • In certain circumstances, for example OAR proximity, this may be individualized
- 54. OAR delineation
- 55. Atlas of lung, esophagus, and spinal cord Int J Radiat Oncol Biol Phys. 2011 81(5):1442-57 Recommendation based on Timmerman et al for RTOG 0236 and RTOG 0618, Bezjak et al for RTOG 0813
- 56. Atlases for Organs at Risk (OARs) in Thoracic Radiation Therapy • Feng-Ming (Spring) Kong MD PhD • Leslie Quint MD • Mitchell Machtay MD • Jeffrey Bradley MD
- 57. Lungs • Both lungs should be contoured using pulmonary windows. • The right and left lungs can be contoured separately • Total lung for dosimetry • All inflated and collapsed, fibrotic and emphysematic lungs should be contoured. • Hilar region and trachea/main bronchus should not be included in this structure
- 58. Esophagus • Begin at the level just below the cricoid to its entrance to the stomach at GE junction. • Contoured using mediastinal window/level on CT to correspond to the mucosal, submucosa, and all muscular layers out to the fatty adventitia. • Barium swallow for better delineation.
- 59. Spinal cord • Bony limits of the spinal canal. • Start at the level just below cricoid to the bottom of L2 • base of skull for apex tumors and continuing • Neuroformanines should not be included.
- 60. Begin below the level of post-cricoid region
- 61. Include the entire spinal canal
- 62. Barium swallow allows better delineation of esophagus
- 63. Barium swallow
- 65. Inferiorly till the GE junction
- 66. Pericardium • Includes pericardial fatty tissue, part of great vessels, normal recesses, pericardial effusion (if present) and heart chambers. • Starts at one slice above the top of aortic arch, ends at the last slice of heart apex at diaphragm. • Pericardium includes the heart.
- 67. PericardiumSVC Begin one slice above the top of aortic arch
- 71. Pulmonary V
- 72. Descending aorta
- 76. Great vessels • Contoured separately from the heart, using mediastinal windowing to correspond to the vascular wall and all muscular layers out to the fatty adventitia. • Start at least 3 cm above the superior extent of the PTV and up to at least 3 cm below the inferior extent of the PTV. • For right sided tumors, SVC will be contoured, and • For left sided tumors, the aorta will be contoured. • The ipsilateral PA will be delineated for tumor of either side.
- 77. Pulmonary AAscending aorta Descending Aorta SVC
- 78. IVC
- 79. Heart • Contoured along with the pericardial sac. • Superiorly begin at the level of the inferior aspect of the pulmonary artery passing the midline and extend inferiorly to the apex of the heart.
- 80. Start at the level of the inferior aspect of the pulmonary artery passing the midline
- 83. Heart and pericardium are to be overlapped
- 84. Proximal bronchial tree • Includes the • distal 2 cm of the trachea, • the carina, • the right and left mainstem bronchi, • the right and left upper lobe bronchi, • the intermedius bronchus, • the right middle lobe bronchus, • the lingular bronchus, and • the right and left lower lobe bronchi.
- 89. Proximal Bronchus Tree Ends at the level of lobar bronchus bifurcating into segmental bronchus
- 90. Brachial plexus • Required for patients with tumors of upper lobes. • Only the ipsilateral brachial plexus is contoured. • Includes the spinal nerves exiting the neuroforamine from top of C5 to top of T2. • Should extend at least 3 cm above the PTV.
- 91. Identify anterior and middle scalene muscles from C5 to insertion onto the first rib. Start at the neural foramina from C5 to T1
- 92. Extend from the lateral aspect of the spinal canal to the small space between the anterior and middle scalene muscles.
- 93. Contour the trunks of the brachial plexus between the anterior and middle scalene muscles.
- 95. Where no neural foramen is present, contour only the space between the anterior and middle scalene muscles
- 96. Contour the trunks of the brachial plexus between the anterior and middle scalene muscles.
- 97. Eventually the middle scalene will end in the region of the subclavian neurovascular bundle.
- 98. Vein, artery, and nerve (VAN, anterior to posterior) will go over the 1st rib and under the clavicle Contour the brachial plexus as the posterior aspect of the neurovascular bundle.
- 99. IV contrast greatly facilitates contouring The first and second ribs serve as the medial limit
- 102. Chest wall • Autosegmented from the ipsilateral lung with a 2-cm expansion in the lateral, anterior, and posterior directions. • Anteriorly and medially, it ends at the edge of the sternum. • Posteriorly and medially, it stops at the edge of the vertebral body with inclusion of the spinal nerve root exit site. • Includes intercostal muscles, nerves exclude vertebrate bodies, sternum and skin. This recommendation was based on 1. Kong et al, Int J Radiat Oncol Biol Phys. 2010 Oct 7. 2. “CW2cm consistently enabled better prediction of CW toxicity than CW3cm” in Mutter et al, Int J Radiat Oncol Biol Phys. 2011 Aug 23.
Editor's Notes
- #39: Pitch = Table travel per rotation/Beam width Helical Approach – Philips approach - Combine image data at same phase from several respiratory cycles Cine approach – GE - Acquire limited thickness image data at specific phases in respiratory cycle
- #44: The registration is made based on the nearest neighbor criterion, where at each slice location the image is selected so that its phase is closest to each phase bin.
- #45: Even if a 4DCT scan is of a very high quality with few artifacts, the motion of a structure exhibited in a 4DCT scan is still only representative of the motion taking place in the few breathing cycles during which the patient passes through the CT-scanner. It is a movie ‘snapshot’ of the motion.
- #51: Mean IP represents time-weighted location of the tumor
- #91: In contrast to prior RTOG lung studies of contouring the major trunks of the brachial plexus with inclusion of subclavian and axillary vessels, this trial requests contouring the nerves according to the CT anatomy on every other CT slice.