Source Roll Angle Attribute
| Tag | (300A,067A) |
|---|---|
| Type | Conditionally Required (1C) |
| Keyword | SourceRollAngle |
| Value Multiplicity | 1 |
| Value Representation | Double (FD) |
Source roll angle in degrees of the Radiation Source at the Control Point with respect to the Equipment Coordinate System. The angle is a Continuous Rotation Angle, see Section C.36.1.1.5.
See Section C.36.15.1.1 and Section C.36.12.1.1.
Required if the conditions in Section C.36.2.2.5.1.1 are satisfied.
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.36.15.1.1
C.36.15.1.1 Source Roll Angle
For an Equipment Frame of Reference UID (300A,0675) of 1.2.840.10008.1.4.3.1 ([IEC 61217] Fixed Coordinate System Frame of Reference), the source roll angle is the rotation of the [IEC 61217] GANTRY coordinate system about the Y-axis of the [IEC 61217] FIXED coordinate system.
Section C.36.12.1.1
C.36.12.1.1 Equipment Frame of Reference UID
The Equipment Frame of Reference UID (300A,0675) identifies the Equipment Coordinate System for a Treatment Delivery Device, see Section 10.39.1.1.
The RT Radiation SOP Classes are bound by the Standard to specific Well-known Frames of Reference as defined in Table A-2 in PS3.6 . For C-Arm based devices delivering radiation at a single machine isocenter this may be the [IEC 61217] coordinate system. Devices are calibrated to a specific Well-known Frame of Reference and thus use the corresponding Well-known UID in Equipment Frame of Reference UID (300A,0675).
For RT Radiation SOP Classes the result of the transformation between the Patient-based Coordinate System and the Equipment Coordinate System is used to describe the intended treatment position. If two or more transformation matrices describe the relation between two or more Patient-based coordinate systems and a single Equipment Coordinate System, any calculations assuming transitivity via the Equipment Coordinate System must be performed with great care because the patients anatomy may have changed.
For RT Radiation Record SOP Classes the result of the transformation between the Patient-based Coordinate System and the Equipment Coordinate System is used to describe the actual treatment position. In this case the transformation matrices between different Patient-Based coordinate Systems and a single Equipment Coordinate System shall not be considered transitive from an anatomical point of view and may only be used to compare different treatment positions with respect to the treatment delivery device.
Section C.36.2.2.5.1.1
C.36.2.2.5.1.1 Requirements for Changing Values within RT Control Point Sequence Attributes
This Section specifies when individual Attributes shall be present in a Sequence.
The RT Control Point Sequence specifies a certain order of execution.
At each RT Control Point the value of various Attributes may be specified as an explicit value (which in the case of a type 2C Attribute may be a null value) and if absent remain at the same value as specified previously. There are physical and mechanical implications of specifying a new value as opposed to staying at the same value, for example gear lash, floating point jitter, etc.
At the first Sequence Item in RT Control Point Sequences (i.e., with an RT Control Point Index (300A,0600) equal to 1) all Attributes affected by this Section shall be present if applicable conditions are met.
For Sequence Items other than the first Sequence Item, Attributes shall be present if applicable conditions are met and the value is different from the previously populated value for the same Attribute (in the case of a type 2C Attribute, a null value is considered as a value). The previously populated value is the value from the Item where the Attribute was present with the greatest value of RT Control Point Index (300A,0600) less than the value of the RT Control Point Index (300A,0600) in the current Item.
This means that for an Item in which an Attribute is absent, the application stays at the value of the previously populated Item.
For Sequences inside a RT Control Point Sequence Item, the Sequence shall be present if any of the nested Attributes affected by this Section differ from the corresponding previously populated Item.
For multi-valued Attributes, such as Parallel RT Beam Delimiter Positions (300A,064A), all values shall be present if any value changes.