Brachytherapy Iridium
Describe how iridium wires may be positioned to treat a planar volume.
To treat a planar volume with iridium wires it is necessary to adhere to a system of placement so that the dose profile produced is uniform. For iridium wire the 'modern' nominated schema is the Paris System. This system requires sources that are linear, parallel, equiplanar, equidistant (0.5-1cm), and equistrength. The sources are elongate 15% past the point of intended coverage. The Basal Dose Rate is defined as the dose rate equidistant between the sources, and the Reference Dose Rate (for the purposes of prescription) is 85% of this value.
Describe how a single iridium HDR seed source is used to produce a similar isodose distribution to that of an iridium wire.
A single iridium HDR seed source can simulate an iridium wire by advancing the seed inside a hollow catheter (i.e., a defined linear track) to previously calculated dwell positions for calculated dwell times.
Compare the dose distributions from a Ir-192 point source and an actual Ir-192 HDR brachytherapy source of the same activity.
The point source distribution will be spherical, or to use proper terms, it is isotropic. The actual sources distribution will be flattened at the top, due to the inherent filtration of a source with a physical elongated shape, which is to say that it is anisotropic.
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