Tag | (300A,0688) |
---|---|
Type | Conditionally Required (1C) |
Keyword | RTBeamModifierDefinitionDistance |
Value Multiplicity | 1 |
Value Representation | Double (FD) |
Absolute distance in mm along the z-axis of the Base Beam Modifier Coordinate System from the reference location specified by RT Device Distance Reference Location Code Sequence (300A,0659) to the Beam Modifier Definition Plane.
The value shall be greater than or equal to zero.
Required if RT Device Distance Reference Location Code Sequence (300A,0659) is present.
See Section C.36.1.1.9.
Beam modifiers, e.g., beam limiting devices, compensators and blocks, are specified by geometric coordinates.
A Base Beam Modifier Coordinate System is defined with respect to a parent coordinate system, which may be the Equipment Coordinate System (see Section 10.39.1.1) or another coordinate system derived from the Equipment Coordinate System. Section C.36.12.2 specifies several Well-known Frames of Reference used as the Equipment Frame of Reference, and specifies how a Base Beam Modifier Coordinate System is related to each as a child coordinate system.
The x/y plane of the Base Beam Modifier Coordinate System is referred to as the Base Beam Modifier Definition Plane. The orientation of the Base Beam Modifier Coordinate System is such that the Base Beam Modifier Definition Plane is parallel to the x/y plane of the parent coordinate system. The origin of the Base Beam Modifier Coordinate System is offset from the RT Device Distance Reference Location by the RT Beam Modifier Definition Distance (300A,0688) as shown in Figure C.36.1-1.
Figure C.36.1-1. Base Beam Modifier Coordinate System and a rotated Beam Modifier Coordinate System
Each beam modifier is defined in its own Beam Modifier Coordinate System with the following characteristics:
Defined with respect to the Base Beam Modifier Coordinate System.
Right-handed Cartesian coordinate system, with the positive z-axis pointing towards the nominal Radiation Source location.
The Beam Modifier Coordinate System rotates about the z-axis of the Base Beam Modifier Coordinate System. The orientation at a zero angle about the z-axis is the same as the Base Beam Modifier Coordinate System, i.e., the x- and y-axes are aligned.
The x/y plane of the Beam Modifier Coordinate System is referred to as the Beam Modifier Definition Plane.