DICOM PS3.3 2020c - Information Object Definitions

C.36.15 C-Arm Photon-Electron Beam Module (Current)
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### C.36.15 C-Arm Photon-Electron Beam Module

The C-Arm Photon-Electron Beam Module specifies how a C-Arm photon or electron treatment beam is to be delivered.

Table C.36.15-1. C-Arm Photon-Electron Beam Module Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Number of RT Control Points | (300A,0604) | 1 | Number of RT Control Points in the C-Arm Photon-Electron Control Point Sequence (300A,062F). The value shall be equal to or greater than 2.
C-Arm Photon-Electron Control Point Sequence | (300A,062F) | 1 | Control Points used to model the beam delivery. The number of Items included in this Sequence shall equal the value of Number of RT Control Points (300A,0604).
>Include Table C.36.2.2.6-1 “External Beam Control Point General Macro Attributes”. | DCID 9550 “C-Arm Photon-Electron Delivery Rate Units”.
>Referenced Radiation Generation Mode Index | (300A,0605) | 1C | The value of Radiation Generation Mode Index (300A,0601) in the Radiation Generation Mode Sequence (300A,067B) in this IOD that defines the Radiation Generation Mode used for this Control Point. Required if Number of Radiation Generation Modes (300A,0685) is present and the conditions in Section C.36.2.2.5.1.1 are satisfied.
>Include Table C.36.2.2.9-1 “RT Beam Limiting Device Opening Macro Attributes”.
>Include Table C.36.2.2.11-1 “Wedge Positions Macro Attributes”.
>Source Roll Angle | (300A,067A) | 1C | 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.
>RT Beam Limiting Device Angle | (300A,0679) | 1C | Angle in degrees of the Base Beam Modifier Coordinate System about the z-axis relative to the parent coordinate system. The angle is a Continuous Rotation Angle, see Section C.36.1.1.5. See Section C.36.15.1.2. Required if the conditions in Section C.36.2.2.5.1.1 are satisfied.
>Source to Patient Surface Distance | (300A,0634) | 2C | Distance in mm from the nominal Radiation Source location to the Patient surface (skin) along the central beam axis from the source. Required if the conditions in Section C.36.2.2.5.1.1 are satisfied.
>Source to External Contour Distance | (300A,0132) | 2C | Distance in mm along thecentral beam axisfrom the nominal Radiation Source location to the external contour including devices associated with the patient anatomy model. For dosimetric purposes this value may differ from the Source to Patient Surface Distance (300A,0634). See Section C.36.11.1.4. Required if the conditions in Section C.36.2.2.5.1.1 are satisfied.

#### C.36.15.1 C-Arm Photon-Electron Beam Attribute Description

##### 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.

##### C.36.15.1.2 RT Beam Limiting Device 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 RT Beam Limiting Device Angle (300A,0679) is the rotation of the Base Beam Modifier Coordinate System about the Z-axis of the [IEC 61217] GANTRY coordinate system.

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DICOM PS3.3 2020c - Information Object Definitions