Download An Introduction to Molecular Imaging in Radiation Oncology : A

An Introduction to Molecular
Imaging in Radiation Oncology :
A report by the AAPM Working Group on Molecular Imaging in
Radiation Oncology(WGMIR)
Tuesday Seminar
24th, Dec, 2013
Radiological Physics Lab,
Seoul national university
Seongmoon Jung
Outline
• Introduction
• Molecular Imaging Modalities and Techniques
• Molecular Imaging Challenges in Clinical Radiation
Oncology
• Conclusion
Introduction
• Definition
“ Directly or indirectly monitor and record the spatiotemporal distribution
of
molecular or cellular processes for biochemical, biologic,
diagnostic, therapeutic applications.”
– Radiological Society of North America(2005)
“ The visualization, characterization, and measurement of biological
processes at the molecular and cellular levels in human and other living
things……”
– Society of Nuclear Medicine(2007)
Introduction
• Background
Treatment
Planning
Introduction
• Interest to the radiation oncology community
-
Imaging of biological tumor characteristics
Such as presence of hypoxia, proliferation rate
- diagnosis, radiation treatment, evaluation in the
molecular manner
Molecular Imaging Modalities
and Techniques
Molecular Imaging Modalities and
Techniques
• 5 devices for molecular imaging
(a) PET
(b) SPECT
(c) MRI
(d) Optical imaging
(e) Ultrasound
Molecular Imaging Modalities and
Techniques
A. PET – (1) Basic Principle
•
Simultaneous detection of annihilation X-rays ( two 511 KeV) of a
positron
- coincident event
- random(false) event
- scatter event
•
Positron emitting Radionuclides(Short half life) + biological tracer
molecule(Ligand) to localize in vivo in tissues
Molecular Imaging Modalities and
Techniques
A. PET – (2) Spatial Resolution
•
The finite positron range
- depends on the radioisotope, the type of tissue
•
Noncolinearity of the annihilation photons
•
Pet scanner itself (detector size)
Molecular Imaging Modalities and
Techniques
A. PET – (3) application in oncology
•
FDG to image metabolically active, increased glycolysis
- presence of tumor, inflammation
•
Cerebral blood flow using 15O H2O, tumor hypoxia with 18F
fluoromisonidazole, cell proliferation with 11C thymidine
•
The hybrid PET-CT
A. PET – (4) application in oncology
Molecular Imaging Modalities and
Techniques
B. SPECT –(1) basic principle
• Detection of gamma decay X-rays by radiolabeled agents
• Gamma emitting radioisotopes + Ligand
(99mTc, 111In, 67Ga, 131I, 201Tl )
• Detector called the Anger gamma camera rotated around the object
3 or 6 degree, 120 or 60 projection data
mathematically reconstruction
Molecular Imaging Modalities and
Techniques
B. SPECT – (2) Compared to PET
• Disadvantage
- Using a collimator
reduction of sensitivity
- Less radiation event
poorer spatial resolution
• Advantage
- Multiple radiotracers can be administered and detected
- Relatively long half life radioisotopes
slow biological processes
- Availability for research even at labs far away from cyclotron
facilities
Molecular Imaging Modalities and
Techniques
B. SPECT – (3) application in oncology
• A number of radiolabeled tracer for specific tumors
• In early work, pre- & post- optimization of lung treatment plans
also in brain tumor and malignant lymphoma
• Different organs or functions monitored simultaneously
• Hybrid SPECT-CT in oncology, cardiology and neuropsychiatry
B. SPECT – (3) application in oncology
Molecular Imaging Modalities and
Techniques
C. MRI – (1) Basic Principle
• The origin of signal is the magnetic dipole moment
- External magnetic field(B0)
- RF coil
- Gradient coil
• Signals (SNR, signal-to-noise ratio)
- T1, T2, T2* relaxation time
Molecular Imaging Modalities and
Techniques
C. MRI – (2) Four types of MR
• MRSI
• Perfusion MRI
• Diffusion MRI
• Functional MR(fMRI)
Molecular Imaging Modalities and
Techniques
C. MRI – (3) fMRI & MRSI application
•
MRSI detect, quantify, differentiate neo-plastic disease processes in
the brain, breast and prostate
- By changes of
N-acetylaspartate(NAA) choline lactate, creatine citrate
• fMRI
- Using BOLD (blood oxygen level-dependent) contrast
Relative concentration of deoxyhemoglobin and oxyhemoglobin
C. MRI – (3) fMRI , MRSI application
Molecular Imaging Modalities and
Techniques
D. Optical Imaging – (1) Basic Principle
• Detection of visible and infrared photons transmitted
through biological tissues
• Short penetration depth
- In vitro measurements
- Surface in vivo of small animals
Molecular Imaging Modalities and
Techniques
D. Optical Imaging – (2) Four types
1.
Bioluminescence
2.
Fluorescence – GFP
3.
Diffuse optical tomography(DOT)
4.
Optical coherence tomography(OCT)
Molecular Imaging Modalities and
Techniques
E. Ultrasound
• Development of ultrasound
- Characterization of tissues through Spectral analysis
- Enhancing image quality by the use of specialized contrast agents
• High spatial resolution, real-time imaging
• But poor image quality
Molecular Imaging Modalities and
Techniques
E. Ultrasound
• Contrast Agent, Microbubbles
- Small gas-filled bubbles(1~10μm diameter, 10~200nm shell thickness)
- Provide contrast due to echogenicity of its gas or shell
- Attachment of antibodies, peptides, ligands
• Application
- Blood vessel detection
- Assessment of perfusion and vascular delivery of drugs
- Detection of inflammation and angiogenesis of tumors
Summary
Summary
Molecular Imaging Challenges in
Clinical Radiation Oncology
A. Spatial scale in molecular imaging
B. Image quality
C. Biologic structure definition and response
D. Biological modeling & application for treatment
planning and response assessment
Molecular Imaging Challenges in Clinical
Radiation Oncology
A. Spatial scale in molecular imaging
•
Spatial scale covers 4 orders of magnitude
presents challenges with respect to integrating such data into
a clinical radiation treatment system
•
Although resolution is improving due to technological advantages,
fundamental physical limits exist
Molecular Imaging Challenges in Clinical
Radiation Oncology
B. Imaging Quality
• It depends on a number of complex interacting factors including
- the physical processes affecting the signal
- origination(depth and surrounding tissues)
- spatial & temporal resolution
- noise …..
• Each modality requires specialized QA and quality control
- individual calibration or QA for each patient
• Standardized phantoms, QA tests and benchmark data for various
lesion locations would be valuable for future work
Molecular Imaging Challenges in Clinical
Radiation Oncology
C. Biologic structure definition and response
•
1.
Challenges in radiation treatment
Image transmission
2.
Registration of multimodality images
3.
Image interpretation
4.
Composition of the target and critical volumes from a set of
multimodality image
Molecular Imaging Challenges in Clinical
Radiation Oncology
C. Biologic structure definition and response
•
Accurate image interpretation is required
- Experts
- Software tools
•
Even above challenges are accepted,
the clinical use of molecular images is still challenged by the
needs to define a target volume
•
Biological target volumes for multimodality image sets will not be
congruent in size or shape
Temporal effects must also be addressed when defining the target
•
Molecular Imaging Challenges in Clinical
Radiation Oncology
D. Biological modeling & application for treatment planning and
response assessment
• Predicted models based on biological data from molecular images
provide information to therapeutic decisions and prognoses
• Standardized image acquisition and processing techniques required
To routinely use in biological modeling of radiation dose response
Conclusion
• Molecular imaging is not only imaging a specific cell or molecular
dimensional objects, but also imaging their molecular or biological
processes
• High resolution anatomical imaging + high sensitivity molecular imaging
can achieve volumetric tumor characterization and quantitative
modeling of tissue irradiation
• For the clinical application
- accurate registration
- clinical interpretation of data
- target definition
- image quality
• Great challenges and opportunities for collaborations through the
convergence of molecular biology, diagnostic radiology, radiation
oncology, physics, imaging science, chemistry, and other fields
Discussion & Question
Thank you for your attention !
MRI