Principles and Practice of Radiation Therapy: Chapter 22 – CT Simulation Procedures – Flashcards
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Diagnosis
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• Screening • Cancer Imaging • Pathology • Staging
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Therapeutic Decisions
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• Cure • Palliation • Benign • Surgery/ radiation/ chemotherapy • Patient Interview
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Simulation
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• Fluoroscopy-based • CT simulation • Patient positioning • immobilization devices • digitally reconstructed radiographs (DRRs)
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Treatment Planning
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• Identifying planning target volume • Identifying critical structures • Selection of treatment technique • Isodose distribution • Calculation of treatment beams • Optimization
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Treatment
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• Treatment verification • Dosimetry checks • Treatment delivery & monitoring • Patient assessment • Record keeping
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Patient Follow-Up
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• Patient assessment • Normal tissue response • Tumor control
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Magnetic Resonance Imaging (MRI)
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An imaging technique that relies on cells' responses in a high-intensity magnetic field
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Positron Emission Tomography (PET)
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Visual display of brain activity that detects radioactive glucose in the brain
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Single-Photon Emission Computed Tomography (SPECT)
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Type of nuclear imaging study to scan organs after an injection of a radioactive tracer.
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Four-Dimensional Computed Tomography (4D-CT)
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Uses 3D treatment planning + time
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Intensity-Modulated Radiation Therapy (IMRT)
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Therapy that delivers nonuniform exposure across the radiation field using a variety of techniques and equipment
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Image-Guided Radiation Therapy (IGRT)
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Type of conformal radiotherapy. Conformal radiotherapy can shape the radiotherapy beams around the area of the cancer. Uses X-rays and scans similar to CT scans before and during radiotherapy treatment.
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Virtual Simulation
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Designs fields without a conventional simulator Has better visualization of internal structures by using 3D images on the computer.
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Immobilization Devices
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Assists in the reproducing of the treatment position while restricting movement
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Localization
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Geometric definition of the position and extent of tumor Referenced with surface marks used for treatment setup
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Verification
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Final check to make sure planned treatment beams cover tumor Makes sure there is no irritation of critical normal structures
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Radiopaque Marker
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Material with high atomic number ex: lead, copper, solder wire
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Contrast Media
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Compound used to aid in visualizing structures Has ability to enhance adjacent anatomic structures
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Separation
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Measurement of thickness of patient AP/PA aka Intrafield Distance
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Field Size
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Dimensions of treatment field at isocenter Width x Length
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Digitally Reconstructed Radiograph
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2D image that shows beam's eye view of treatment field. Created at given isocenter
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Interfraction Motion
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Change in target position from one fraction to another
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Intrafraction Motion
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Change in target position during treatment delivery
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Organs at Risk
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Critical structures that may limit the amount of radiation delivered to the tumor volume
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Gross Tumor Volume
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The gross palpable or visible tumor
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Clinical Target Volume
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The gross palpable or visible tumor + surrounding volume of tissue that may contain microscopic diease
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Planning Target Volume
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Clinical target volume + margins for uncertainties
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Internal Target Volume
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Clinical target volume + internal margin that accounts for tumor motion
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Patient Positioning Aids
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Devices designed to place the patient in a particular position for treatment. ex: Head Holders, Knee Wedge, Sponge Pillows, Foam Cushions
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Godfrey Hounsfield
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Developed first computed tomography (CT) unit Shared the 1979 Nobel Prize
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Alan Cormack
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Developed math calculations or algorithms Shared the 1979 Nobel Prize
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CT Simulator RTT Purpose
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High-performance scanner Laser and patient marking system Virtual simulation
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Gantry External Controls
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Couch controls Gantry tilt Emergency off buttons Localizer lasers
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Gantry Internal Controls
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Detector array X-ray tube
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Hounsfield Units
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Shades of gray Electron density of tissue
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Benefits of CT Simulation |
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• Outline critical structures • Delineate target volume • Achieve optimal beam placement • Boost fields planned without patient present
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Benefits of CT Simulation ||
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• Beam's eye view (BEV) • Electronic field shaping • Construction of digital reconstructed radiographs (DRRs) • Calculation of dose distribution
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Considerations and Limitations of CT Simulation
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Bore size Width and shape of couch Laser system Acquisition and patient marking time CT numbers in dose inhomogeneity corrections Setup parameters and treatment accessories unable to be verified Must visualize entire contour
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Presimulation Planning
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• Immobilization • Patient positioning
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Contrast Agents
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• Oral • Intravenous • Intrathecal • Intra-articular
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CT Simulation Treatment Room Sequence
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Room preparation Explanation of procedure Patient positioning and immobilization Data acquisition
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CT Simulation Imaging Sequence
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Target and normal tissue localization Virtual simulation of treatment fields Dose distribution Documenting data
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Components of Image Quality
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• Spatial resolution • Image contrast • Noise • Dose • Artifacts
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CT Image Processing Controls
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• Window width • Window level
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Image Registration
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• Two sets of images • Scans overlaid
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Respiratory Gating
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• Breathing motion artifacts • Four-dimensional scanning • Spirometer • Maximum intensity projection (MIP)
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Stereotactic Radiosurgery (SRS)
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Consists of narrow beams of radiation which are targeted within the brain Immobilization is frame fixed to head
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Stereotactic Body Radiation Therapy (SBRT)
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Administers very high doses of radiation, using several beams of various intensities aimed at different angles to precisely target the tumor.
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Osmolality
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Measure of total number of particles in solution per kilogram of water. (when referring to contrast solution)
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Scan Field of View (SFOV)
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Area for which projection data are collected for CT scan
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Field of View (FOV)
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Encompasses the entire external patient contour
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Maximum Intensity Projection
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Method for 3D data that projects in visualization plane with voxels
