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21 Cards in this Set
- Front
- Back
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FFD
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Focus-to-Film Distance
Focus refers to the simulator x-ray tube focal point. |
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IFD
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Intrafield Distance
Measurement of the patient's thickness along the central axis of the beam from the entrance point to the exit point. This is also known as separation. |
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SAD
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Source-to-Axis Distance
Distance along the beam axis from the front surface of the source to isocenter. |
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TTID
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Tabletop-to-Isocenter
For an isocentric treatment given at mid-depth with the patient flat on the table, TTID = 1/2 IFD & TSD = FAD - 1/2 IFD |
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If the patient is not flat on the table...
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TTID = 1/2 IFD + Posterior Air Gap
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TSD
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Target-to-Surface Distance
Target refers to the x-ray tube focal spot and the surface refers to the surface of the patient at the central axis. |
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CA
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Central Axis of the treatment field.
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Posterior Air Gap
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The distance between the patient's body surface and the supporting surface under the patient.
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Main issue that image guided radiotherapy (IGRT) addresses...
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...the interfraction movement of both target volumes and critical normal structures.
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What are the two technological developments resulted in the ability to perform complex treatment planning in three dimensions and the manipulation of images in real time?
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1. Increase in computing power
2. Development of computer graphics |
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List some of the limitations of the Sim-CT in the 1990s
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1. Heat capacity of the x-ray tube generally meant that only a few slices could be scanned
2. The time taken to scan was limited to approx. one rev. per minute, motion artifacts were introduced creating images of a poorer quality that those produced on a diagnostic scanner. 3. Uncertainty of Hounsfield Units (HU), dose variation not exceeding 3% for photon beams in the range of 6-18 MeV. 4. Relatively high dose to the patient which was shown to be approx. 10X that delivered with a diagnostic scanner under similar conditions. |
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What is DICOM?
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Digital Imaging Communications in Medicine
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Define DICOM.
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A standard for handling, storing, printing and transmitting information in medical imaging
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What does DICOM do?
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Defines the formats for medical images that can be exchanged with data and quality necessary for clinical use. DICOM is implemented in almost every radiology, cardiology imaging and radiotherapy device.
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What is the current release of DICOM?
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Version 3.0
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What is DICOM RT?
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The extension of the DICOM 3.0 standard which handles the radiotherapy modality.
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What is the propose of positioning lasers?
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The lasers intersect at or define the treatment machine isocenter.
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What do the lasers do?
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The lasers provide visual reference for proper patient alignment.
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What do the lasers define?
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Patient location in three dimensions. They are longitudinal, lateral and vertical.
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In conventional simulation, where are the lasers positioned?
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They are fixed as the simulation table can mimic the movements of the treatment table. Upon completion of imaging, the target is defined and the laser reference points are marked/ tattooed.
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How is the couch adjusted in CT simulation?
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The patient is temporarily marked with reference points before scanning. After the target volume has been determined, the computer calculates isocenter with reference to the temp. marks and the couch adjusts automatically.
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