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:

  • T - Simple universal scaling factor.
  • T(r) - T is a function of distance from the source.
  • T(d,μ) - T is a function of path length in the silicone carrier.
  • T(r,d,μ) - T is a function of both distance from the source and path length in the silicone carrier.
  • no T - The carrier is considered to be nearly water equivalent (e.g. ROPES plaques).
  • 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.
  • Silicone Oil Attenuation - When calculating the attenuation of radiation as it passes through the eye, the vitreous humor is, by default, assumed to be 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.
  • 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.
  • Gold Backing - accounts for loss of backscatter that might have originated from behind the plaque, and low energy flourescence emitted from the face of the plaque, that results from the near complete absorption of all primary emissions that were directed towards the plaque shell.
  • Air Interface - accounts for a small reduction in backscatter originating from the air in front of the eye compared to an infinite water environment.