Imrt Where Next Image Guided Radiotherapy


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  • Imrt Where Next Image Guided Radiotherapy

    1. 1. IMRT: Where next? Image guided Radiotherapy Dr. A. W. Beavis PhD Principal Physicist, Hull and East Yorkshire Hospitals (NHS) Trust (Hon) Senior Research Fellow, University of Hull
    2. 2. Thank you for this honour! <ul><li>Mme Naudy and the organisers of this training meeting </li></ul><ul><li>Great honour for me and my hospital to be invited back to speak on this course for a second time </li></ul><ul><li>Hope you enjoy my lecture! </li></ul><ul><li> </li></ul>
    3. 3. IMRT is possible in any clinic! <ul><li>Now have the weaponry to treat small volumes of tissues to high(er) doses </li></ul><ul><li>Need to develop the ‘intelligence’ to find the tissue to target! </li></ul><ul><ul><li>Recall that target volume delineation is as bigger part of the prescription as defining the doses </li></ul></ul><ul><li>Need to ensure we are treating the right tissues! </li></ul>
    4. 4. ‘ Limitation’ of current IMRT planning at PRH and world-wide <ul><li>CT imaging does not show the position or viability of tumour </li></ul><ul><li>Solutions: </li></ul><ul><li>Advanced MR techniques </li></ul><ul><ul><li>Spectroscopy/ T2 mapping </li></ul></ul><ul><ul><li>DCE </li></ul></ul><ul><li>Also PET imaging </li></ul>
    5. 5. CMS:Focal FUSION used to fuse T2-weighted images with CT data set Use of T2 weighted images routine in our department for planning purposes
    6. 6. Can we just add images together from different modalities? <ul><li>Do we expect the ‘prostate’ on a CT scan from Monday to overlay on the ‘prostate’ on an MR scan acquired the next Thursday? </li></ul><ul><li>No, because organs move, ‘fill-up’/ empty and generally try to confuse us! </li></ul>Courtesy Di Yan, William Beaumont and Marcel Van Herk, NKI Amsterdam
    7. 7. GE Lightspeed CT-PET combined scanner Should we obtain images at same point in time? So we KNOW the anatomy is registered.
    8. 8. But just discussed organs move...? <ul><li>So information about position and magnitude of motion is required </li></ul><ul><li>So in planning we either need to build in motion margins (ICRU50) or know precisely where each organ is during treatment </li></ul><ul><li>maybe stratify patients as ‘good/ bad’ Conformal RT candidates </li></ul>T = 0 T = t Z = z 1 Z = z 2 Z = z 3
    9. 9. PTV is an envelope within which the CTV is present with 100% certainty <ul><li>Cannot assume any edge of the PTV is less at risk from being under-irradiated </li></ul>DEFINE MARGINS CAREFULLY – EVEN WITH ADVANCED IMAGING! + +… ’ 95%’ isodose = +
    10. 10. Where are we going? Image guided radiotherapy <ul><li>Planning the treatment </li></ul>
    11. 11. Defining the Boost target in IMRT ? <ul><li>Much interest in Magnetic Resonance Spectroscopy MRS for this purpose </li></ul><ul><ul><li>UCSF: Pickett et. al. IJROBP 44 (4) 921-929 (1999) and references therein. </li></ul></ul><ul><li>Look for decreased ‘Citrate’ and enhanced ‘Choline’ traces in the spectra </li></ul><ul><li>MRS is not simple to do and it is time consuming to perform necessary studies </li></ul>
    12. 12. <ul><li>IMRT offers the capability to BOOST the dose to the actual tumour – potentially increasing the tumour control probability </li></ul>+ ? = PTV1: Prostate PTV2: Boost the conventional dose?? 55 Gy covering PTV1 65 Gy ‘covering’ PTV2 PTV2 is covered by 60 Gy
    13. 13. Spectroscopy data for Peripheral Zone (PZ) Carcinoma and normal PZ data <ul><li>Single voxel measurements showing normal PZ Citrate sample and that for diseased (Ca.) tissue </li></ul>tumour normal Choline Citrate Choline Citrate <ul><ul><li>G.P. Liney et al. NMR in Biomedicine 12 39-44 (1999) </li></ul></ul>T2 image showing MRS sampled voxels
    14. 14. Tumor Necrosis Normal NAA Cr Cho Cho Combination of MRI and 3D-MRSI >>> acquisition of an “image of spectra” MR-Spectroscopy Imaging (MRSI) Courtesy of Prof. Lynn Verhay, UCSF
    15. 15. Voxel size 1cc MRSI 3D contours Abnormality-Index 2 , 3 , 4 Courtesy of Prof. Lynn Verhay, UCSF
    16. 16. Our approach <ul><li>Though our MR group has experience in single voxel MRS they opted for the use of ‘T2 maps’ rather than expanding to multi-voxel MRS </li></ul><ul><ul><li>G.P. Liney et al. ‘Proton MR T2 Maps correlate with the Citrate Concentration in the Prostate’ NMR in Biomedicine 9 59-64 (1996) </li></ul></ul><ul><li>T2 map is a plot of the absolute T2 value/ relaxation time (rather than signal intensity) </li></ul>
    17. 17. T2 map .v. spectroscopy (MRS) <ul><li>Advantages: </li></ul><ul><ul><li>short acquisition time compared to MRS </li></ul></ul><ul><ul><li>produces anatomical image with mm resolution </li></ul></ul><ul><ul><ul><li>no need for registration to T2 weighted image </li></ul></ul></ul><ul><ul><li>modern scanners produces T2 map image as part of programmed sequence (Philips Intera 1.5T) </li></ul></ul><ul><li>Disadvantage: </li></ul><ul><ul><li>don’t see Choline data (not clear if this is important) </li></ul></ul><ul><ul><li>biopsy false-negatives - blood and urine in Prostate will cause high T2 signal! </li></ul></ul><ul><ul><li>Biopsy false-positives – this high signal will fade with time (darken image) as fluid disperses </li></ul></ul>
    18. 18. T2 maps: of volunteer and patient – alternative to MRS and potentially directly applicable into RT planning. <ul><li>T2 map of healthy volunteer with normal Peripheral Zone image </li></ul>T2 map of patient with tumour in Peripheral Zone Dark area indicates disease <ul><li>Advantages of T 2 mapping over MRS: </li></ul><ul><li>short acquisition time compared to MRS </li></ul><ul><li>produces anatomical image with mm resolution (no registration needed) </li></ul>Absolute T2 value .v. Citrate concentration <ul><ul><li>G.P. Liney et al. NMR in Biomedicine 9 59-64 (1996) ‘Proton MR T2 Maps correlate with the Citrate Concentration in the Prostate’ </li></ul></ul>
    19. 19. Dynamic contrast-enhanced-MRI <ul><li>Gadolinium: Gd-DTPA </li></ul><ul><li>Shortens the T1 and T2 signal – enhances image on a T1 weighted image </li></ul><ul><li>Basically, it enhances the signal from the dense vascularisation (and poor integrity) typical of neoplastic (tumour) tissue </li></ul><ul><li>Normal tissue does NOT enhance as quickly </li></ul><ul><li>Relevant to most solid tumours </li></ul><ul><ul><li>Citrate chemistry is unique to prostate. </li></ul></ul><ul><ul><li>G.P. Liney et al. NMR in Biomedicine 12 39-44. (1999) </li></ul></ul>Another method (relevant to more tumours):
    20. 20. 1’38’’ 2’10’’ 4’53’’ t = 0 Enhancement factor, EF(t) Tumour (volume) in PZ Benign disease in CG: BPH Normal tissue i.e. RHS of PZ shows no/little uptake T1 weighted images at different time intervals post contrast injection. Don’t use rectal probe for Radiotherapy sequences!
    21. 21. Transfer of information into the Radiotherapy Treatment planning process 2 The data obtained from ‘tracking’ the progress of the Contrast during the T 1 scan (the DCE scan) can be analysed in several ways to extract spatial information to provide the treatment planning process. The simplest is to threshold the data set to identify all pixels that ‘enhanced’ above a certain (pre-determined) value. Plot of enhancement factor .v. time for a T 1 -DCE sequence obtained for a RT patient. A threshold analysis has identified those pixels in the shaded area as being viable tumour
    22. 22. Dynamic Contrast-Enhancement <ul><li>Acquire baseline images pre-contrast </li></ul><ul><li>Multiphase post-contrast </li></ul><ul><li>Uptake of tumour can be analysed </li></ul><ul><li>Parameter map produced </li></ul>
    23. 23. Threshold the pixels that indicate tumour, XiO/ FOCAL contouring tools can pick it out T2-Weighted FSE Image overlay generated from DCE analysis added on Can now contour the tumour without further expert Radiology knowledge Use automatic contouring tools to pick these areas out and delineate them Transfer the information into the Radiotherapy Treatment planning system
    24. 24. Plot of enhancement factor .v. time 1 2 3 1 2 3 ROI 3 (orange) Dark bit of PZ on T2 image – could have interpreted as tumour – but DCE indicates it’s a benign problem T2 image with an overlay generated from the DCE fused on
    25. 25. <ul><li>We are currently already performing (Radiology) DCE method on other sites </li></ul><ul><li>Working on their usefulness in Radiotherapy planning </li></ul><ul><li>DCE showed nodal involvement and chest wall/ muscle </li></ul><ul><li>infiltration not seen on planning CT performed 3 days previously </li></ul>
    26. 26. Summary of process 1 <ul><li>Obtain T 2 weighted volumetric data set of images </li></ul><ul><li>Inject contrast </li></ul><ul><li>obtain a time series of T 1 weighted images (at same location and resolution as above T 2 set) </li></ul><ul><li>Analyse data and produce a parameter map providing spatial info of viable tumour </li></ul>
    27. 27. Summary of process 2 <ul><li>Fuse the parameter map and the T 2 weighted images to provide tumour and relational anatomy information </li></ul><ul><li>‘ DICOM’ to FOCUS and in FOCALfusion register to planning CT </li></ul><ul><li>FOCALSim – perform contouring </li></ul>+
    28. 28. Summary of process 3 <ul><li>Produce inverse plan in CMS: FOCUS/ XiO </li></ul><ul><li>Create a simultaneous boost IMRT plan </li></ul>PTV1: Prostate PTV2: MRI delineated disease (white = CTV) 60 Gy ‘covering’ PTV2 52.5 Gy covering PTV1
    29. 29. Role of DCE in verification of (conventional) radiotherapy efficacy? Enhancement factor plots .v. time for a patient before conventional radiotherapy. Plots after treatment Plot of PSA level .v. time. A represents the time of the pre-Radiotherapy MRI-DCE scan and B the post-treatment scan. A B A B
    30. 30. <ul><li>Left handed 21 year old with a glioma in the left frontal lobe </li></ul><ul><li>T 2 -weighted fast spin-echo (TE/TR=100/3640 ms) 3D T 1 -weighted fast spoiled gradient-echo (TE/TR/flip = 4.2/13.4ms/20 0 ) </li></ul><ul><li>fMRI acquisition (self-paced finger-thumb opposition with the right hand). T 2 * -weighted (TE/TR/flip=50/300 ms/90 0 ) </li></ul>Activation plot Functional MRI for conformal avoidance
    31. 32. 7.2 % 29.6 % 34.6 % MC (IMRT_OAR) MC (IMRT_noOAR) MC (Conv) Dose Volume Histogram
    32. 33. Reproducibility fMRI Series 2 Series 1 Series 3 0.605 0.605 0.572 Correlation Coefficient
    33. 34. Repeated imaging on volunteers <ul><li>Area highlighted is consistent with patient data </li></ul><ul><li>Intra session repeats show consistent data </li></ul><ul><li>Inter session repeats show consistency </li></ul><ul><li>Developing this further to create tests to feed probability density maps into inverse planning driven by biologically defined cost functions (EUD approach) </li></ul><ul><ul><li>Wiesmeyer and Beavis AAPM abstract </li></ul></ul><ul><ul><li>ESTRO abstracts ……. </li></ul></ul>
    34. 35. Conclusion <ul><li>Inverse planning/ IMRT allows us to deliver different dose levels to multiple targets simultaneously </li></ul><ul><li>Using MRI - We are developing methods to enhance the identification of diseased sites and definition of boost target volumes for IMRT </li></ul><ul><li>Concentrating on Prostate, Brain and Head and Neck (YCR grant) – but any solid tumour is possible! </li></ul>
    35. 36. Thanks to: <ul><li>Dr. Gary Liney </li></ul><ul><li>Prof. Lindsay Turnbull – MRI/ Radiology </li></ul><ul><li>My colleagues in Hull </li></ul><ul><li>Prof. Lynn Verhay - UCSF </li></ul><ul><li>Dr. Andrea Pirkzall - UCSF </li></ul>CMS for their interest and financial support in our research work Also for funding my participation in this meeting