Imaging Techniques in Radiation Therapy

Transcription

1 Imaging Techniques in Radiation Therapy Wuhan University Medical Physics Course June 5, 2015 Jianguo Qian, PhD, DABR Medical Physicist Department of Radiation Oncology & Molecular Radiation Sciences Johns Hopkins University

2 Statement All materials used in this lecture were used for teaching purpose only without commercial or financial interest. Some materials in this lecture may come from public internet and previously collected resources whose original sources could not be identified. If you notice any material missing appropriate citation, please let me know.

3 Outline X-ray Imaging (2D & 3D) Magnetic Resonance Imaging (MRI) Nuclear Medicine Imaging (Scintigraphy, SPECT & PET) Ultrasound Imaging (Ultrasonography)

4 X-ray 2D Imaging Radiography Mammography Fluoroscopy Angiography Linac-based MV & kv imaging

5 X-ray System Principle of an X-ray system with image intensifier. X rays impinging on the image intensifier are transformed into a distribution of electrons, which produces an amplified light image on a smaller fluorescent screen after acceleration. The image is observed by a television camera and a film camera and can be viewed on a computer screen and stored on a CD-ROM or a PACS.

6 X-Ray Imaging Principle The intensity of the transmitted beam as a function of the attenuation coefficient of the pixels traversed. Top part, the intensity after crossing one volume element; bottom part, after traversing n volume elements

7 First medical imaging technology Radiography Became possible after physicist Wilhelm Roentgen discovered X- rays on November 8, 1895 First radiograph ---- Roentgen s hand

8 Radiography Systems

9 Fluoroscopy Real-time radiography, i.e. continuous acquisition of a sequence of x-ray images over time, essentially a realtime x-ray movie of the patient.

10 Mammography A radiography system specifically designed for breast imaging using much lower x-ray energies (usually ~30kVp)

11 Angiography Angiography (or arteriography) is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers.

12 Angiography and Liver Cancer Johns Hopkins Medicine Department of Gastroenterology & Hepatology

13 Types of Angiography Conventional Angiography (CA) Digital Subtraction Angiography (DSA) CA and DSAs at three progressive time points during contrast material injection Hendee & Ritenour, Medical Imaging Physics, 4 th Edition, Pg.245

14 Linac-Based X-ray Imaging System Purpose 1. Verify treatment setup patient position and iso position 2. Verify aperture shape of treatment fields (MV)

15 Linac-Based MV 2D Imaging Du, et al., JACMP, 11(4):3297, 2010

16 Linac-Based kv 2D Imaging Department of Radiation Oncology, UCSD

17 SRS/SBRT imaging ExacTrac System Cyberknife

18 X-ray 3D Imaging Computed Tomography (CT) 4D CT CBCT 4D CBCT

19 CT Principle Abdullah et al., Optical Engineering, 52(3),

20 CT Reconstruction E. Kristensson, et. al, Opt. Express 20, (2012);

21 CT Reconstruction Algorithms Courtesy of Mark Bangert through Matlab Central

22 CT Evolution 1 st generation 2 nd generation 3 rd generation 4 th generation 5 th generation Hendee & Ritenour, Medical Imaging Physics, 4 th Edition, Pg.254, 257

23 CT Scanning Mode Sequential scan (step-and-shoot) and Spiral scan (continuous) Single-slice scan and multi-slice scan Radaideh, M. M. et al. (2001). Using multi-slice spiral CT scanner: The principles you need. The University of Texas MD Anderson Cancer Center.

24 CT Application in Treatment Planning Delineation of target volume and the surrounding structures in relation to the external contour Providing quantitative data (in the form of CT numbers) for tissue heterogeneity corrections

25 CT scanner and CT simulator Special features of CT simulator Flat table top Laser system Software

26 CT simulation with ordinary CT scanner Create new CT number to density table Put on a flat table Using small X-ray opaque ball bearings (BBs) and embedded lasers on CT to mark patient AAPM TG-66

27 CT Calibration CT dose - a measure of dose delivered during a scan CT resolution ability to distinguish two very small objects in close proximity CT contrast - ability to resolve relatively large objects with small density difference from background CT uniformity evaluation of CT image noise and artifacts CT geometry ability to accurately reproduce patient dimensions and shape in CT images without distortion CT number ability to accurately represent density of objects

28 CT Phantoms CTDI Phantom ACR Phantom CatPhan 700 Philips Daily QA phantom

29 CatPhan CT AAPM TG-66

30 CT number to density table Purpose in Pinnacle planning system: Look up mass attenuation coefficients and Scale the dose deposition kernel to include the effects of inhomogeneities on scattered radiation CIRS RMI

31 RMI Phantom Data

32 CT Density Curve Saw, et al., Med Dosim. 2005, 30(3):145-8

33 CT Artifacts Definition: A distortion or error in an image that is unrelated to the subject being imaged.

34 Source of CT Artifacts Patient Imaging protocols Imaging processes Equipment

35 Typical CT Artifacts Metal artifact Beam hardening artifact Ring artifact Motion artifact

36 Reason: Presence of metallic objects Solution: Remove external metallic objects Using metal artifact reduction image reconstruction algorithm, such as Philips OMAR Metal Artifact

37 Beam Hardening Artifact Reason: Hardened beam is less attenuated by tissue Solution: Inrease beam energy (kv) Decrease slice thickness Adding filter (bowtie for CBCT)

38 Ring Artifact Reason: One or more detector having malfunction or failure Solution: Scanner recalibration Detector replacement Image: St-Amant M., et al. on

39 Motion Artifact Reason: Voluntary patient motion Involuntary patient motion Solution Voluntary: Use positioning aids Explain to patient Involuntary: Use fast scanning protocol Audio or video coaching, Use motion management procedure such as 4D CT

40 4D CT One more dimension was involved in CT imaging Patient breathing phase or amplitude (or, time) Series of CT data are collected with the patient free-breathing and correlated to patient s respiratory trace Multi-phase reconstruction of the same scanned area can easily show the displacement of a lesion over time, during the normal respiration cycle. 4DCT allows the clinician to evaluate the tumor and tumor motion, plan a more accurate radiotherapy treatment.

41 Tumor motion effect Traditional CT MIP of 4D CT

42 Courtesy of Peter Maxim, Stanford University 4DCT GE LightSpeed + RPM RPM system Patient setup 4D CT workstation Select phase(s) 4D planning GE cine mode Infrared reflective markers Infrared camera

43 Real-time Position Management RPM software records respiratory trace (i.e., vertical block position vs. time)

44 4D CT scanning on GE Cine mode: step-and-shoot; multiple gantry rotations at each bed position

45 4D CT scan phase 50%

46 4DCT Philips Brilliance + Bellows Courtesy of John Givens, Philips Healthcare Inc.

47 The Philips Bellows Device A pneumatic mechanism measuring changes in pressure caused by respiratory motion via a transducer linked to the Brilliance CT scanner.

48 Amplitude vs Linear Phase Binning Phase-based binning can produce badly misaligned slices within an image volume 0% 25% 50% 75%

49 Amplitude vs Linear Phase Binning Phase-Based Amplitude-Based

50 Cone Beam CT (CBCT) MacDonald-Jankowski DS, Asian Journal of Oral and Maxillofacial Surgery 2006;18:

51 Linac-based kv CBCT Zhen, et al., 2012 Phys. Med. Biol

52 Linac-based MV CBCT Department of Radiation Oncology, UCSF

53 CBCT-guided Linac D. Jaffray et al. Int J. Radiat. Oncol. Biol. Phys. 2002

54 CBCT Scanning Mode Son, et al., JACMP 15(2), pp.4556, 2014 Lehmann, et al., JACMP 8(3), pp.2354, 2007

55 CBCT-guided radiation therapy

56 CBCT-guided radiation therapy

57 Linac-based 4D CBCT 4D CBCT 8x84 projections 3D CT 670 projections Sonke, AAPM 2006 summer school

58 MRI Principle Typical MRI Images MRI Application in Radiation Therapy Image Fusion MRI-based planning MRI-guided radiation therapy system

59 MRI Basics Nuclear Magnetic Dipole Moment : Spinning Charge P = No Net Magnetization Hydrogen

60 Dipole Moment of Bulk Hydrogen B 0 Net Magnetization

61 Longitudinal Relaxation (T1) and Transverse Relaxation (T2) Hendee, et al., J. Med :

62 MRI Images T1WI T2WI PDWI DWI ADC GE Perfusion images fmri BOLD images MRA MRV Post-Gd images Volumetric images MR arthrograms FLAIR STIR Etc Presentation of Kulkarni, K., NHS UK

63 Typical MRI images T1-weighted: Fat bright, good for look at brain structure Usually for normal anatomical details T2-weighted Water and fluid brighter, ideal for tissue oedema Usually for pathology since tissues with disease tends to have higher water content FLAIR Fluid Attenuation Inversion Recovery Water suppression technique, good for cerebral oedema and periventricular or cortical lesions STIR Short T1 Inversion Recovery Fat suppression technique, good for adrenal glands, bone marrow and fatty tumors Weegenaar C, Magnetic Resonance Imaging e-tutorial

64 T1-weighted vs T2-weighted MRI - White matter appears a light grey in T1 and a dark grey in T2. - Grey matter appears grey in both. - Cerebrospinal fluid (CSF) appears black in T1 and white in T2. Weegenaar C, Magnetic Resonance Imaging e-tutorial

65 FLAIR

66 MRI application in radiation therapy Used to delineate anatomical structures or treatment target accurately Image fusion Target volume determination such as Y90 brachytherapy MRI-based treatment planning MRI-guided treatment device

67 MRI vs CT MRI advantage - Excellent and controllable soft tissue contrast Figure 1 (A, B): A 16-year-old boy developed altered sensorium followed by loss of consciousness. Plain CT scan (A) shows a hyperdense lesion (arrow) in the right frontoparietal region, with surrounding white matter edema and mass effect. Axial plain T1W MRI (B) at the corresponding level shows a hyperintense periphery (arrow) due to presence of intracellular methemoglobin and central hypointensity (arrowhead) due to deoxyhemoglobin Kembhavi, et al. Neuroradiology, 22(2), pp98-105, 2012

68 MRI-CT fusion Figure 1. Axial CT- 3T MRI scan fusion. The red line is the MRI-delineated prostate contour, the purple line is the CTdelineated prostate contour and the blue line is the contour of the rectum delineated on CT-MRI fusion. Ingrosso, et al. Open Journal of Radiology, 1(1), 2011

69 MRI-based Treatment Planning Current stage: MRI/CT based Process CT scan + MRI scan Register MR contours to CT (rigid/deformable) Transfer MR contours to CT data set Planning Future: MRI alone radiation treatment planning (RTP)

70 Challenges for MRI-based RTP No electron/physical density information MRI geometric distortion Magnetic field inhomogeneity Nonlinear gradients from RF excitation Displacement of signal from actual location

71 Density-Assigned MRI-based RTP Comparison of isodose distributions between (a) MRI W -based, (b) MRI W+B -based, (c) MRI W+B+A -based, and (d) CT-based inverse-optimized IMRT plans for Patient 2. Images were obtained at the identical axial level based on CT-MRI registration. Isodose distributions were calculated on CT with heterogeneity correction to standardize comparisons. Dark blue segment delineates PTV70. White and black arrows highlight areas of under- and over- coverage, respectively Chin, et al., JACMP, 15(5) 4851, 2014

72 MRI-guided Radiotherapy System Viewray MRIdian system

73 MRIdian Components Courtesy of Lasitha Senadheera, ViewRay Inc.

74 CBCT vs MRI

75 Nuclear Medicine Imaging (NMI) X-ray, CT, MRI or ultrasonography Basically transmission imaging Mainly provide structural (anatomical) information May consist true physical parameters NMI Basically emission imaging Mainly provide functional information: physiology, metabolism, biochemistry at molecular level

76 Isotopes in Clinical NMI Adapted from presentation of Frederic H. Fahey, Harvard Medical School

77 NMI Modalities Scintigraphy (2D) Single photon emission computed tomography (SPECT) Positron emission tomography (PET)

78 Scintigraphy and SPECT Gamma ray Parallel Collimator or Pinhole Collimator Pixellated Scintillator object Photons PSPMT Thansverse view

79 A Mouse-Sized Scintigraphy Detector

80 Scintigraphy Lactating Mouse Mice with tumors Each mouse was injected with about 14 µci Na 125 I.

81 Parallel-Hole SPECT Coronal images Sagittal images The mouse was injected with about 14 µci Na 125 I. Transaxial images

82 Pinhole SPECT 130 µci Na 125 I; Two-pinhole helical SPECT 200 µci Na 125 I; Two-pinhole helical SPECT

83 Scintigraphy Application in Radiation Therapy Lung shunt fraction determination for Y-90 Therasphere liver cancer brachytherapy Figure 4: During the mapping angiogram phase, 5 mci of technetium-99m labeled macroaggregated albumin was injected within the right hepatic artery to quantify the liver-lung shunt. The planar scintigraphic images demonstrate distribution of the radiotracer within the right lobe of the liver without any abnormal extrahepatic distribution. Regions of interest were drawn within the lungs and liver resulting in an estimated maximum lung shunting of 3%. Chamarthy, Case Rep Radiol. 2012:236732

84 SPECT Application in Radiation Therapy Assess cardiac toxicity of RT in breast cancer patients using myocardial perfusion SPECT Lung perfusion SPECT-guided IMRT planning to reduce dose delivery to highly functional lung McGuire, et al.,phys Med Biol. 2010;55(2):403-16

85 PET Li Z., et al. Advanced Drug Delivery Reviews 62 (2010)

86 PET Detector Siemens Healthcare Inc.

87 Clinical SPECT vs PET SPECT Resolution degrade with increasing object-detector distance Limited sensitivity, difficult for dynamic imaging Longer half-life radioisotope Less expensive PET Resolution has less dependence on object-detector distance High sensitivity, feasible do dynamic imaging Limited half-life radioisotope Expensive

88 PET Application in Radiation Therapy Functional image-guided radiation therapy planning (PET/CT) Adaptive radiation therapy

89 PET-guided radiation therapy planning Department of Radiation Oncology, UCLA

90 PET-guided Adaptive Radiation Therapy Grootjans, et al., Nature Reviews Clinical Oncology, 2015

91 Ultrasound Imaging Advantage High sensitivity Technically easier to use Bedside test No radiation/contrast exposure Safe and well accepted Less expensive and widely available Disadvantage Operator-dependent Limited penetration (obesity) Small field of view False-negative in case of superficial and rare lesion

92 Ultrasound Imaging Basics Perry Sprawls, Ultrasound Production and Interaction

93 Two Major Effects Piezoelectric effect (Ultrasound probe, or transducer) Electric field causing certain crystal oscillate mechanically, thus generating acoustic waves ressure variation on the crystal causing electric potential Acoustic impedance A measure of how difficult the sound go through the material Defined as speed of sound x density of material Ultrasound reflections (echoes) are caused by variations in acoustic impedance of materials on opposite sides of the interfaces

94 A-mode and B-mode Scans A-mode Time/Amplitude B-mode Intensity Imaging Yale Fisher, Essential lectures in Ophthalmic Ultrasound

95 Ultrasound Image Courtesy of Wu Liu, Yale University

96 Ultrasound-based Prostate Seed Implant Brachytherapy Ultrasound image-based pre-implant planning

97 Ultrasound-based Prostate Seed Implant Brachytherapy Real-time ultrasound-guided implant procedure

98 Ultrasound-based Prostate Seed Implant Brachytherapy CT-based post-implant seed position verification

99 Ultrasound-guided Radiation Therapy Elekta Clarity

100 Thank you!