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The source-to-film distance is used to calculate the amount of shift of the X-ray target between image positions.
True
Patient motion between films is always desirable for accurate radiation dose calculation.
False
The orientation of the radiograph is irrelevant for the computer's dosimetry system.
False
Dummy sources are used to align the source position in the computer for radiation dose calculation.
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Radiation dose can be prescribed without reconstructing the pathways of the radiation source.
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Radiographic techniques can only be performed when after-loading applicators are active.
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Image reconstruction is not necessary for source localisation from conventional radiographs.
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The active sources can be identified by their radiopaque markers.
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IGRT in brachytherapy stands for Intensity Guided Radiation Therapy.
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Fluoroscopy can be used to acquire 3D sets of images.
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Ultrasound provides higher resolution and sharpness compared to fluoroscopy.
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Radiation dose calculation in brachytherapy is done using the AAPM TG43 algorithm.
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Patient motion correction is not an important aspect in brachytherapy.
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In brachytherapy, the treatment planning development has shifted from 2D to 3D.
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Traditional radiographs are a practical and efficient method for source localisation in brachytherapy.
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Inverse planning in brachytherapy is done using the HIPO algorithm.
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The reference point is defined as the intersection of the beam central axis and the film.
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The orthogonal radiographs are used to determine the x and z coordinates of the source.
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The Pythagoras theorem is used to calculate the distance between two points in 3D space from their 2D projections.
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The standard film position direction is always PA and LAT.
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The rotation axis of the x-ray target is the x-axis.
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The source coordinates on the film must be converted to coordinates within the patient using a linear transformation.
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The determination of the distance between two points requires the definition of a base line perpendicular to the edge of the films.
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The usage of two orthogonal films allows for the calculation of the radiation dose.
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Study Notes
Source Localization in Brachytherapy
- Conventional radiographs are used to digitize the sources and origin, and an algorithm converts the film coordinates to patient coordinates.
- The algorithm involves a mathematical transformation, and the source-to-film distance (SFD) and source-to-reference point distance are used.
- Ideally, there should be no patient motion between films.
Source Localization from Conventional Radiographs
- It is easier and safer to perform radiographic techniques when after-loading applicators are inactive.
- The orientation of the radiograph must be correct for the computer's dosimetry system.
- Dummy sources with radiopaque markers are used to identify the source position.
Methods of Source Localization
- Direct measurement
- Orthogonal radiograph
- An isocentric technique
- Semi-orthogonal method
- Stereo shift films
Source Localization from Orthogonal Radiographs
- Two orthogonal films are used, and sources must be identified and matched on each film.
- The reference point (origin) is digitized into the computer.
- The beam central axis passes through the reference point and is perpendicular to the film.
Digitizing Radiograph Images for Planning
- Coordinates x, y, and z are obtained from the AP and lateral films.
- The common coordinate y is the rotation axis of the X-ray target.
Determining the Distance between Points
- Pythagoras' theorem is used to determine the distance between points.
- A baseline common to both films is defined, often perpendicular to the intersection of the radiographs.
Brachytherapy Setup
- I-125 and Pd-103 are used with activities of around 0.3mCi and 1.7mCi, respectively.
- The radioactive seeds are planted in the prostate about 0.5 to 1 centimeter apart.
Source Localization: Ultrasound
- Advantages: can be performed intraoperatively, allows visualization of prostate, needles, and seeds, and allows 3D imaging acquisition and live imaging.
- Disadvantages: lower resolution and sharpness, lower contrast, and spatial distortion.
Source Localization: Fluoroscopy
- Advantages: can be used intraoperatively, provides sharper and higher contrast images.
- Disadvantages: ionizing radiation, cannot be used to acquire 3D set of images, and does not visualize soft tissues.
IGRT in Brachytherapy
- Image-guided brachytherapy is used to improve treatment planning.
Treatment Planning Development
- Shifting from 2D to 3D, target volume definition, algorithm: AAPM TG43 to Monte Carlo, inverse planning using IPSA and HIPO.
Summary
- Source and target localization are crucial in brachytherapy.
- Traditional radiographs, CT, ultrasound, and fluoroscopy have their advantages and disadvantages and can complement each other.
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Description
This quiz covers the process of converting film coordinates to patient coordinates in radiography, involving mathematical transformations and X-ray target shift calculations.
