When Slot Collimation is enabled from this menu, or by the Lipped vs Slotted button in the toolbar of the Prescription window, collimation by the gold slot of an EP plaque of primary radiation emitted from a source is included in the dose calculation.
For all COMS plaques, slot collimation should be disabled and shell collimation enabled as illustrated in the example menu to the left.
For all EP plaques, slot collimation should be enabled and shell collimation optionally disabled.
NOTE: When slot collimation is enabled for small and medium size EP plaques there is usually no need to simultaneously enable Shell Collimation because virtually all primary radiation is collimated at the face surface of the gold slot surrounding the source. Including both Slot and Shell collimation greatly lengthens the calculation time because it requires ray tracing the path of primary radiation between a calculation point and each source and testing for collision with the thousands of triangles that model the shell instead of, or as well as, the closest 10 triangles that model slot collimation. As illustrated below, enabling Shell collimation for this medium size plaque in addition to Slot collimation results in the same 2D dosimetry but takes significantly longer to calculate.