3D Surface Imaging for PBI Patient Setup

Transcription

1 3D Surface Imaging for PBI Patient Setup G.T.Y. Chen 1, Ph.D., M. Riboldi 2, Ph.D. Christoph Bert 3, Ph.D., D.P. Gierga 1, Ph.D. 1 Massachusetts General Hospital Harvard Medical School 2 TBMLab - Department of Bioengineering Politecnico di Milano University 3 GSI Darmstadt, Germany

2 WG Conner 1975 Motion detection /cancellation imaging JA Purdy 1978

3 Video-based patient set-up 2-Dimensional: 3-Dimensional: video images with single / orthogonal cameras laser interferometry - surface height maps stereo-photogrammetry - point-based registration - surface registration accuracy simplicity Marco Riboldi

4 3-D point-based stereo-photogrammetry Control room Bunker Sync-power and composite video Motion Analyzer gantry Digital data TVC 2 IR flash radiation beam TVC 1 IR flash CPU 3-D markers coordinates Isocenter localization control points

5 Applications of 3-D point-based stereo-photogrammetry G Baroni, CAS 2000 Breast irradiation

6 3-D surface scanning G Baroni, MBEC 2003 Breast irradiation Opto-electronic surface sensing Hybrid registration (surface fiducials / laser spots JW Sohn, AAPM 2004 Breast irradiation Handheld laser scanning

7 2-D patient set-up: Recent References / Others 1. Milliken BD, Rubin SJ, Hamilton RJ, Johnson LS, Chen GT. Performance of a video-image-subtraction-based patient positioning system. Int J Radiat Oncol Biol Phys Jul 1;38(4): Johnson LS, Milliken BD, Hadley SW, Pelizzari CA, Haraf DJ, Chen GT. Initial clinical experience with a video-based patient positioning system. Int J Radiat Oncol Biol Phys Aug 1;45(1): D point-based stereo-photogrammetry: 1. Rogus RD, Stern RL, Kubo HD. Accuracy of a photogrammetry-based patient positioning and monitoring system for radiation therapy. Med Phys May;26(5): Baroni G, Ferrigno G, Orecchia R, Pedotti A. Real-time opto-electronic verification of patient position in breast cancer radiotherapy. Comput Aided Surg. 2000;5(4): Soete G, Van de Steene J, Verellen D, Vinh-Hung V, Van den Berge D, Michielsen D, Keuppens F, De Roover P, Storme G. Initial clinical experience with infrared-reflecting skin markers in the positioning of patients treated by conformal radiotherapy for prostate cancer. Int J Radiat Oncol Biol Phys Mar 1;52(3): Weiss E, Vorwerk H, Richter S, Hess CF. Interfractional and intrafractional accuracy during radiotherapy of gynecologic carcinomas: a comprehensive evaluation using the ExacTrac system. Int J Radiat Oncol Biol Phys May 1;56(1): Surface registration: 1. Moore C, Lilley F, Sauret V, Lalor M, Burton D. Opto-electronic sensing of body surface topology changes during radiotherapy for rectal cancer. Int J Radiat Oncol Biol Phys May 1;56(1): MacKay RI, Graham PA, Logue JP, Moore CJ. Patient positioning using detailed three-dimensional surface data for patients undergoing conformal radiation therapy for carcinoma of the prostate: a feasibility study. Int J Radiat Oncol Biol Phys Jan 1;49(1): Baroni G, Troia A, Riboldi M, Orecchia R, Ferrigno G, Pedotti A. Evaluation of methods for opto-electronic body surface sensing applied to patient position control in breast radiation therapy. Med Biol Eng Comput Nov;41(6): Sohn J, Kim S, Chvetsov A, Suh T, Jin H, Farr J. Three-Dimensional Surface Image Registration For Image-Guided IMRT To Breast. AAPM 2004 Proceedings.

8 Clinical Implementation of IGRT for PBI : Microcosm Multiple Approaches to IGRT Organ deformation Respiration Quantify accuracy of methods Apply statistical rigor to IGRT Etc

9 Challenge: Setup of Breast Irradiate involved quadrant of breast (vs. whole) 4.0 Gy X 8 fractions BID / 4 days (vs. 6 wks) Escalate dose; minimize NT irradiation Mini tangents and electron boost

10 Imaging Options Image target (seroma( seroma) directly (in room CT) Surrogates (more commonly used) Skin tattoos aligned to lasers Chest wall imaged in radiographs Breast surface 3D video imaging (new) Clips near seroma imaged by radiographs

11 Sources of Uncertainty Elasticity of skin, arm position / lasers Chest wall is weakly coupled to tumor / breast tissue Skin /seroma correlation - deformation affects accuracy Clip migration / seroma shrinkage affects radiographic accuracy Conebeam CT before not during Rx

12 Outline: 1) System Description 2) System Performance 3) Patient Studies 4) Target Registration Analysis 5) Summary

13 1. Surface Imaging Hardware POD 1 Linac1 Linac2 (Protons) POD 2 AlignRT Gantry

14 Each pod contains. Speckle Camera Flash Projection Texture Cam Speckle Camera

15 Speckle image Two camera pods Flash mode Speckle pattern 6 images captured Surface coords in 3D Surface matching to maximize congruence between reference and Rx surfaces Torso phantom

16 Reconstructed surface image

17 Wire Frame Obj images Zoomed Surface Patch

18 Interactive Demo Use file Marco 2006 phantom.obj D:\Research Projects 06\spine 3d video\viewer viewer\surfaceview.exe

19 3D Surface Alignment Process (analogous to conventional IGRT) Define reference surface (CT or 1 st Rx) Acquire daily surface image (after laser setup) Match daily 3D image with ref image through surface matching Adjust patient position (Verify post move)

20 Alignment Screen ROI 4 DOF 6 DOF Standard Couch

21 2.Characterize System Performance What is the smallest misalignment detectable by this 3D video system? Performed phantom and calculational experiments to measure system performance. C. Bert et al Medical Physics 2005, M Riboldi 2006

22 Ground Truth High precision mechanical stage (digital micrometer, 1/100 mm) Breast phantom

23 Phantom Surface Model ROI

24 Determine System Accuracy Acquire reference surface Move mechanical stage known amount Acquire daily surface image / query system how much did it move? Compare ground truth (known move) with AlignRT calculated shift.

25 Phantom Study Results 18 readings / data points range of shifts: [-2, +2] mm in each direction (VRT, LNG, LAT) compared AlignRT-suggested shifts vs. digital micrometers (ground truth) Translation differences [mm] VRT LNG LAT 3-D MEAN SD Minimum detectable translational shifts is sub-mm.

26 Phantom virtual experiment High precision mechanical stage (digital micrometer, 1/100 mm) Can system detect small angular misalignments? VRT LNG LAT

27 Results 6 DOF transformation parameters Virtual phantom experiment mean±sd differences [mm] [deg] VRT LNG LAT ROT PR1 PR2

28 3.Patient Studies Analyze multiple methods of PBI setup (Laser, Chest Wall, Iris, AlignRT) Comparative / quantitative analysis of method accuracy. Metric: residual displacements on target localization after alignment (Target( Registration Error) Data analysis performed on a statistical basis (non parametric Friedman ANOVA and Wilcoxon tests)

29 Patient Imaging Protocol Patient aligned by lasers Orthogonal IRIS images: Clip based move Treat Image SM L Image SM T Image SM E DRRs from CT SM R from CT SM T1 as reference for VisionRT TRE evaluation

30 Breast Alignment Analysis

31 4.Target Registration Error The TRE is the vector difference between the target as aligned by method a,b,c and ground truth. Ground truth: defined by clips (DRRs, Planning CT)

32 Laser TRE Align breast by laser; take radiographs of clips (ground truth). Calculate shifts needed to bring clip into congruence with ref image clip position (TRE of Lasers) Lasers GT

33 Chest Wall (CW) TRE Begin Begin with perfect IRIS clip alignment; align CW to ref DRR; vector difference is CW TRE Ant Ant Inf Clips T Sup Inf Clips T T Sup Chest Wall Chest Wall Post Post Chest Wall alignment

34 AlignRT TRE Begin with perfect IRIS clip alignment; match surfaces; apply transformation to isocenter. Difference vector is AlignRT TRE. Surface mismatch TRE Matched surfaces

35 IRIS (radiographic) System Berbeco et al Phys Med Biol 2004:49: X-ray Tube retract IRIS Steve Jiang Greg Sharp Ross Berbeco Detector Arms retract

36 Radiographic (IRIS) TRE Acquire IRIS radiographs; calculate shifts; make shifts; re-image, DIPS. IRIS TRE is inexactness in repositioning patient EXACTLY to t calculated shift; ie residual error in setup. IRIS alignment

37 TRE Analysis Results 1.4 TRE analysis 3D TRE [cm] Medians Laser:.79 cm Iris:.22 VRT.32 CW: Laser Iris VisionRT CW Median 25%-75% Min-Max

38 Statistical Analysis Is there a meaningful difference between Laser, Iris, Chest Wall and VisionRT TREs? YES -> Friedman ANOVA test (p< ) Where is the difference? Wilcoxon rank test: LASER vs IRIS LASER vs AlignRT IRIS vs AlignRT CW vs LASER p< p< p<0.21 p<0.11

39 Statistical Analysis Results Laser, Iris, CW and VisionRT can be divided in 2 groups, in terms of TRE results: CW Laser Median TRE 6-8 mm Iris AlignRT Median TRE 2-3 mm

40 Question If the intrinsic accuracy of surface based alignment is <0.5mm (as shown in precision phantom experiments), then why are patient TRE s on the order of 3mm? (TRE of IRIS radiographic clip alignment is about 2mm) Deformation? Respiration? Other effects?

41 SMT2 SMT3 SMT4 SMT5 SMT6 SMT7 SMT8 Is there breast deformation? Patient 4: Generally, reference surface and treatment surfaces are within 2mm after 6 DOF fit. (green areas)

42 Patient 5

43 Can we use CT Breast Surfaces as reference image? Rx: Lt Breast Rx: Rt Breast Estimated magnitude using GE Workstation to measure Pt 4 ~ 5 mm; Pt 5 ~ mm

44 Texture Images reveal setup

45 Ongoing Studies: TRE as a function of breast size and height above chest wall. Protocol extended to 300 PBI patients. Intra-fractional dosimetric variations due to breathing

46 Why surface imaging if we have ground truth by clips? Faster guide to optimal position, verify as needed Reduce radiation in comparison to radiographs Surveillance during Rx Not every machine has conebeam CT or OBI Applications in charged particle beam radiotherapy.

47 5.Summary Determined that TRE of 3D surface imaging system superior to conventional methods. Applied statistics to provide significance Respiration remains issue if accuracy < 2 mm is desired. Deformation is minimal in patients studied 3D technology promising for PBI setup

48 Acknowledgements Steve Jiang,Greg Sharp, Julie Turcotte Simon Powell, Alphonse Taghian, Angela Katz, Ellen Kornmehl MGH Radiation Therapists Technical advice: Norman Smith / Ivan Meir VisionRT Study conducted under IRB protocol.

49 References Bert, C et al: A phantom evaluation of a stereovision surface imaging system for radiotherapy patient setup Med Phys 32: Bert, C. et al: Initial Clinical Experience with Surface Imaging for PBI: Int J Rad Onc Bio Phys March 15, 2006 Riboldi, M: submitted for publication 2006 Gierga,, DP: Oral presentation at ASTRO 2006