Different information Xray CT PET Xray computed tomography

  • Slides: 30
Download presentation
Different information X-ray CT PET X-ray computed tomography Positron emission tomography Anatomy/ Form Metabolism/

Different information X-ray CT PET X-ray computed tomography Positron emission tomography Anatomy/ Form Metabolism/ Function PET/CT Complementary Information (Wikipedia)

Simulation of X-ray CT and radiotherapy Robert L. Harrison University of Washington Medical Center

Simulation of X-ray CT and radiotherapy Robert L. Harrison University of Washington Medical Center Seattle, Washington, USA Supported in part by PHS grants CA 42593 and CA 126593

Nuclear Medicine Radiology Radiotherapy (www. imaginis. com) (Stieber et al) (Wikipedia)

Nuclear Medicine Radiology Radiotherapy (www. imaginis. com) (Stieber et al) (Wikipedia)

Simulation Comparison

Simulation Comparison

National lab simulations • Simula�te everything and anything. • Very slow.

National lab simulations • Simula�te everything and anything. • Very slow.

Simulation Comparison

Simulation Comparison

CT simulation

CT simulation

Analytic simulation (Visible Human Project®) • In an analytic simulation we ‘do the integrals’.

Analytic simulation (Visible Human Project®) • In an analytic simulation we ‘do the integrals’.

Beam-hardening (Bushberg) • X-ray tubes produce a range of energies. • Lower energy photons

Beam-hardening (Bushberg) • X-ray tubes produce a range of energies. • Lower energy photons are more easily scattered/absorbed. • The x-ray beam gets ‘harder’ (a higher percentage high energy photons) as it passes through the object.

Scatter • Collimation reduces scatter to acceptable levels. • Scanners with larger detector areas

Scatter • Collimation reduces scatter to acceptable levels. • Scanners with larger detector areas do have problems.

Analytic CT simulation • For every camera line-ofresponse, step a beam through the voxelized

Analytic CT simulation • For every camera line-ofresponse, step a beam through the voxelized object. – Steps can be constant size or to next boundary. • At each step, reduce beam strength to account for attenuation. – Can use the current voxel’s attenuation or interpolate. (De Man)

Other issues • Partial volume (beam is not infinitely thin, several tissue types in

Other issues • Partial volume (beam is not infinitely thin, several tissue types in voxel). – Use finer discretization. • Beam hardening. – Simulate at several energies, then sum. • Patient motion. – Do a series of simulations at different positions. (De Man)

Radiotherapy simulation

Radiotherapy simulation

Types of radiotherapy • Photon irradiation. • Other particle irradiation. • Radioactive seed implantation.

Types of radiotherapy • Photon irradiation. • Other particle irradiation. • Radioactive seed implantation.

Killing a tumor • Radiotherapy attempts to – maximize dose to tumors. – minimize

Killing a tumor • Radiotherapy attempts to – maximize dose to tumors. – minimize dose to normal tissues. (Heron)

Types of radiotherapy • Photon irradiation.

Types of radiotherapy • Photon irradiation.

Huge doses Organ Whole body Tumor Heart Liver LD 50 Dose (Grays) 3 -5

Huge doses Organ Whole body Tumor Heart Liver LD 50 Dose (Grays) 3 -5 50 - 40 30 (Mc. Garry)

Fractionation • Split dose into fractions to allow tissues to heal. – 2 Gray/day,

Fractionation • Split dose into fractions to allow tissues to heal. – 2 Gray/day, 5 days/week, 56 weeks. • Normal tissue recovers more quickly. • Most tumors have hypoxic/necrotic (low oxygen/dead) centers. – Time for these areas to develop blood supply. (Stieber)

Dose tolerance (Mc. Garry)

Dose tolerance (Mc. Garry)

Multiple beams • Multiple beams focused on tumor. – Maximum dose occurs where beams

Multiple beams • Multiple beams focused on tumor. – Maximum dose occurs where beams converge. – Dose to particularly sensitive organs can be avoided or reduced with beam placement. (www. impactscan. org)

Simulate dose deposited

Simulate dose deposited

Typical simulator Nucletron Oldelft Simulix-HQ

Typical simulator Nucletron Oldelft Simulix-HQ

Virtual or CT simulation • Software simulation of radiotherapy. – Beginning to replace physical

Virtual or CT simulation • Software simulation of radiotherapy. – Beginning to replace physical simulation for many situations. – CT scan used for input data.

Radiation therapy vs. CT (www. impactscan. org)

Radiation therapy vs. CT (www. impactscan. org)

Large bore

Large bore

Virtual simulator • Segments patient into organs. • Allows user to specify beam intensity,

Virtual simulator • Segments patient into organs. • Allows user to specify beam intensity, shape, position. • Keeps track of – – – Total organ/tumor dose. Maximum organ dose. % organ over threshold dose Minimum tumor dose. % tumor under threshold dose. (www. impactscan. org)

Simulation features • • Semi-automatic anatomy/tumor definition. 3 D visualization. Beam’s eye view. Field

Simulation features • • Semi-automatic anatomy/tumor definition. 3 D visualization. Beam’s eye view. Field shaping. Dose histogramming. Symmetric or asymmetric dose margins. Fast.

Take away • Simulation of x-ray CT and radiotherapy uses analytic simulation. – Too

Take away • Simulation of x-ray CT and radiotherapy uses analytic simulation. – Too many photons to track. – Integrate % of beam escaping for CT. – Integrate dose deposition for radiotherapy. • X-ray CT produces density maps. • Radiotherapy – Treatment planning attempts to maximize the dose to tumor, minimize the dose to normal tissue. – Dose tolerance of organs varies widely. – Simulation used to optimize treatment. • Hardware or software.

References J. T. Bushberg, The essential physics of medical imaging, Lippincott Williams & Wilkins,

References J. T. Bushberg, The essential physics of medical imaging, Lippincott Williams & Wilkins, 2002. B. De Man et al, Metal Streak Artifacts in X-ray Computed Tomography: Simulation Study, IEEE Transactions on Nuclear Science, 46: 3: 691 -696, 1999. K. P. George et al, Brain Imaging in Neurocommunicative Disorders, in Medical speech-language pathology: a practitioner's guide, ed. A. F. Johnson, Thieme, 1998. D. E. Heron et al, FDG-PET and PET/CT in Radiation Therapy Simulation and Management of Patients Who Have Primary and Recurrent Breast Cancer, PET Clin, 1: 39– 49, 2006. E. G. A. Aird and J. Conway, CT simulation for radiotherapy treatment planning, British J Radiology, 75: 937 -949, 2002. R. Mc. Garry and A. T. Turrisi, Lung Cancer, in Handbook of Radiation Oncology: Basic Principles and Clinical Protocols, ed. B. G. Haffty and L. D. Wilson, Jones & Bartlett Publishers, 2008. R. Schmitz et al, The Physics of PET/CT Scanners, in PET and PET/CT: a clinical guide, ed. E. Lin and A. Alavi, Thieme, 2005. W. P. Segars and B. M. W. Tsui, Study of the efficacy of respiratory gating in myocardial SPECT using the new 4 -D NCAT phantom, IEEE Transactions on Nuclear Science, 49(3): 675 -679, 2002. V. W. Stieber et al, Central Nervous System Tumors, in Technical Basis of Radiation Therapy: Practical Clinical Applications, ed. S. H. Levitt et al, Springer, 2008. P. Suetens, Fundamentals of medical imaging, Cambridge University Press, 2002. www. impactscan. org/slides/impactcourse/introduction_to_ct_in_radiotherapy