Dose Calc. Options

Dose Calculation Options

The Dose Calc. Options menu selects which factors are applied to the dose calculation. YOU SHOULD VERIFY THE SETTINGS IN THIS MENU or in the Rx Window toolbar PRIOR TO PERFORMING A DOSE CALCULATION !!! The affected factors are anisotropy, linear vs point source, a correction for plaques with silicone carriers, a scatter correction, lip collimation, slot collimation, and dose constants.

This menu also provides access to the physics data files loaded by PS when it is launched for review and validation of changes to those files.

From the Dosimetry menu:

Shell Collimation - enables ray-tracing of the collimation of primary radiation by the plaque shell. Very fast for circular plaques, about 10X slower for irregular plaques and plaques with notches. Enabled by default for COMS and ROPES plaques, disabled for EP slotted plaques to increase calculation speed since almost all collimation in a slotted plaque results from collimation by the slot rather than the shell.
Slot Collimation - enables ray-tracing of the collimation of primary radiation by the rectangular slot surrounding a seed. Enabled by default for EP slotted plaques, disabled for COMS and ROPES plaques.
Partial Exposure - Calculates fraction of primary radiation from a linear source which does not pass through the shell. Enabled by default.
Unlock Physics... - Opens the physics window with permission to edit the physics data. Requires the physics password that was set when licensing PS.
Physics... - Opens the physics window for viewing only.

Anisotropy F(r,θ) - enables the anisotropic source model (vs an isotropic source). Anisotropy is enabled by default for all plaques.
Linear Sources - Enables the linear source model (vs a point source model). The linear source model is enabled by default for COMS, ROPES and EP plaques.
Carrier Attenuation - Enables calculation of attenuation due to the higher effective Z (compared to water) of the silicone carrier of COMS plaques. Enabled by default ONLY for COMS plaques.
Scatter - this hierarchical menu accesses dosimetric corrections which attempt to compensate for the lack of a homogeneous full scatter geometry.
Ray Trace Linear Attenuation - enables ray tracing of the primary radiation path. When ray tracing is enabled, the path length of primary radiation emitted from seed-like sources as it traverses regions of varying density and effective atomic number is accounted for. For example, ray tracing must be enabled in order to estimate the additional attenuation resulting from silicone oil substitution of the viteous. Default values for the density of water at 37 °C, the relative densities of many ocular anatomic regions compared to water, and the effective atomic number of these ocular regions (e.g. cornea, sclera, lens, vitreous, aqueous, nerve, tumor, tissue and air are found in preference eye settings. Most of these values fall within about 8% of water, so ray tracing is disabled by default and the density of water is simplifed to 1.0 g/ml in order to accelerate dose calculations. However, ray tracing may be optionally enabled if you feel the need. The most noticable effect is increased attenuation in the lens and silicone substitution of the vitreous
Substitute Silicone Oil - When calculating the attenuation of radiation as it passes through the eye, the vitreous humor is, by default, assumed to be nearly water equivalent. If the vitreous will be replaced by silicone oil, enable this option to correct for the greater linear attenuation coefficient of silicone oil compared to water. The correction is performed by ray tracing the primary radiation path through the vitreous humor. The linear attenuation coefficient for silicone oil is found in the Dose Constants tab of each radionuclide's physics file and may need to be customized for whichever silicone oil variant you are using. Applicable only to gamma sources. Disabled by default.
Limit β Near Field - Limits the distance that a calculation point can approach a β patch. Enabled by default.