DICOM Standard Browser

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Data synced with official DICOM standard on 18 April 2024. The DICOM Standard is under continuous maintenance, and the current official version is available at http://www.dicomstandard.org/current/. DICOM Parts 3, 4, and 6, © NEMA. Please note that the most recent PDF version of the standard is the official reference, and should checked when making technical decisions.

Beam Modifier Orientation Angle Attribute

Tag (300A,0645) Required (1) BeamModifierOrientationAngle 1 Double (FD)

Angle in degrees of the Beam Modifier Coordinate System with respect to the Base Beam Modifier Coordinate System. The angle is a Continuous Rotation Angle, see Section C.36.1.1.5.

The direction from thick edge to thin edge is along the positive y-axis of the Beam Modifier Definition Plane.

See Section C.36.1.1.9 and Section C.36.2.2.10.1.1.

Section C.36.1.1.5

C.36.1.1.5 Continuous Rotation Angle

A Continuous Rotation Angle is an angle in the range (-∞,+∞).

Continuous Rotation Angle represent a rotation direction and magnitude. The magnitude is not limited to be between 0 and 360 degrees.

All rotations are defined in a right-handed coordinate system, thus the direction of a positive rotation is seen as clockwise when viewed in the positive direction of the axis of rotation.

Section C.36.1.1.9

C.36.1.1.9 Beam Modifier Coordinate System

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.