4D-MRI for Radiotherapy of moving Tumours: Latest developments, comparison to 4D-CT Vancouver, August 2, 2011
Indications for Radiotherapy of Lung Cancer primary radiotherapy in NCSLC - stage III Oertel et al., Radiologe 2010;50:669 674 Haasbeek et al., Lung Cancer 2009;64,1 8 - Pancoast tumour + stages I-II if surgery not possible before surgery - Pancoast tumour after surgery -pn2 - after incomplete resection (R1, R2)
Improvements in Lung Cancer Radiotherapy Improvements in LC radiotherapy Increased demand of appropriate multi-modality diagnostic imaging
LC RT Planning: Motion Adapted RT static CT 4D-CT 4D-CT 4D-CT Beam ON plan under assumption of tu. displacement detection of tu. displacement plan in knowledge of tu. displacement gating for tu. position
LC RT Planning: Motion Adapted RT ex. PTV2 w/ motion compensation PTV1 w/ ideal motion adaption in. PTV2 - PTV1= IPPT individual potential to preserve tissue
Capturing respiratory Motion with CT prospective techniques slow helical CT insp./exp. CT integrating igtv over time breathing command or external trigger step-by-step cine CT external signal (belt) retrospective techniques low pitch helical CT external signal (belt)
Capturing RM with CT: insp./exp. Scanning standard CT Flash-CT Flash-CT Flash-CT static breathing breathing (trigger in.) (trigger ex.) Hintze et al., Exp. Rad. 2010, Kiel
Capturing RM with CT: Step by step Cine CT Step-by-Step (e.g. GE) Detector width Exp Insp Z
Capturing RM with CT: Step by step Cine CT Advantages robust against changes of respiration frequency no overranging at z-limits respiration triggering easy Disadvantages Z-coverage incomplete w. changes of respiration depth every single position waists 180 rotation
Capturing RM w/ CT: Low Pitch helical 4D-CT Low Pitch helical CT (e.g. Siemens, Toshiba) Exp Insp Z
Capturing RM w/ CT: Low Pitch helical 4D-CT Advantages more effective use of projections changes in respiration frequency better tolerated Disadvantages Z-coverage incomplete with changes of respiration depth (use lowest pitch cave dose and imaging time) overranging at z-limits
4D MRI as an Alternative? - if soft tissue contrast in CT is poor (e.g. liver) - if minimizing radiation dose is important - if multiple respiratory cycles have to be covered
Capturing respiratory Motion with MRI slow acquisition integrating igtv over time MIP reconstruction prospective techniques triggered acquisition navigator technique external signal (belt) fast/ultrafast time resolved display of respiratory motion 2D + t 3D + t = 4D retrospective techniques reassorting/binning oversampled data by external signal by internal signal ( self-navigated )
Capturing RM with MRI: Integrating igtv/t - acquisition of 2D-SS-GRE (TrueFISP) at 3/s - MIP of non-assorted images ( slice stacking ) - volume/area agree with step-by-step 4D-CT Adamson et al., Med Phys 2010;37:5914 5920
Capturing respiratory Motion with MRI Hypothesis: Robustness against respiratory motion is achieved with the same technology that would produce 4D image data correlated with respiratory motion!
Dynamic CE MRI: Navigator Motion Correction A hybrid breathhold/navigator-triggered approach Hintze C, Biederer J, et al. RöFo 2010;182: 45-52
Capturing RM with MRI: Retrospective Binning 3D-flash (GRE) retrospective (G. Remmert, DKFZ) Remmert et al., Phys Med Biol 2007;18:N401-N405
The Future: self navigated 4D-MRI Evolution of self-navigated MRI Respiration belt Navigator technique self-navigated MRI: 3D flash self-navigated MRI: Radial/KWIC
Capturing RM: Self-navigated 3D flash MRI Weick S, Proc. 17 th Sc. Meeting, ISMRM, 2009 1) 3D flash free breathing 2) quasi-random k-space ordering 3) non-spatially encoded DC signals from k-space center > determination of respiratory cycle 4) grouping of acquisitions for respiratory phase > expiration or multiple phases (S. Weick et al., Würzburg)
Capturing RM: Self-navigated radial MRI Lin W et al., Magn Reson Med 2008;60:1135 1146 1) radial data acquisition 2) signal from k-space center > determination of respiratory cycle 3) grouping of views for respiratory phase > expiration or multiple phases 4) further improvements of image quality autofocusing - 3D image correlation - K-space-weighted image contrast (KWIC) - principal component analysis
Experimental Set up for 4D Imaging 4 5 Artificial Thorax 3 2 1
LC RT: Comparison 4D-CT/4D-MRI/4D-CBCT 4D-CT 4D-Cone beam CT 4D-MRI - 4D-MRI and CBCT overestimate lesion size - 4D-MRI and CBCT underestimate displacement - 4D-MRI and CBCT with less reproducibility Biederer J et al. (2007), RSNA 2007, ISMRM 2007 Biederer J et al., Int J Radiat Oncol Biol Phys. 2009;73: 919-926
4D-CT vs. 4D-MRI for LC RT: Comparison Biederer J et al., JMRI 2010;32:1388 1397
4D MRI for LC RT: Perspectives - might replace 4D-CT for RT planning in the future - ideal for selection of patients - will profit from faster acquisition schemes TWIST 4D MRI 2.5 vol/s Courtesy of J. Dinkel, DKFZ