DICOM PS3.3 2021d - Information Object Definitions

C.36.2.2.14 RT Accessory Holders Definition Macro (Current)
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##### C.36.2.2.14 RT Accessory Holders Definition Macro

This Macro defines the geometric configuration elements which cannot vary during delivery and which are used to hold accessories such as blocks or compensators.

Table C.36.2.2.14-1. RT Accessory Holders Definition Macro Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Number of RT Accessory Holders | (300A,0670) | 1C | Number of RT Accessory Holders defined in the RT Accessory Holder Definition Sequence (300A,0614). Required if RT Radiation Physical and Geometric Content Detail Flag (300A,0638) equals FULL. May be present otherwise.
RT Accessory Holder Definition Sequence | (300A,0614) | 1C | Accessory Holder device definitions. Required if Number of RT Accessory Holders (300A,0670) is present and has a non-zero value. The number of Items included in this Sequence shall equal the value of Number of RT Accessory Holders (300A,0670).
>Include Table C.36.2.2.3-1 “RT Accessory Device Identification Macro Attributes”. | DCID 9518 “Radiotherapy Accessory No-slot Holder Device Types”. DCID 9519 “Radiotherapy Accessory Slot Holder Device Types”.
>Device Index | (3010,0039) | 1 | Index of the Device in this Sequence. The value shall start at 1 and increase monotonically by 1.
>Referenced Defined Device Index | (300A,0602) | 1C | Device Index value that links the device defined by this Sequence Item to the corresponding device in an RT Radiation Instance. The device identification of the two devices may or may not be the same. The value is the index of a device in the RT Accessory Holder Definition Sequence (300A,0614) within the single SOP Instance referenced by Referenced RT Instance Sequence (300A,0631). Required if the Instance referenced in Referenced RT Instance Sequence (300A,0631) contains the device that corresponds to the device defined by this Sequence Item. See Section C.36.2.2.8.1.5.
>Beam Modifier Orientation Angle | (300A,0645) | 1 | 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. See Section C.36.1.1.9.
>RT Accessory Holder Water-Equivalent Thickness | (300A,060D) | 2 | Water-Equivalent thickness in mm of the Accessory Holder parallel to the radiation beam axis.
>RT Accessory Holder Slot Existence Flag | (300A,060F) | 1 | Indicates whether the RT Accessory Holder has slots in which other RT Accessory Holders or beam modifying devices can be inserted. Enumerated Values: YES The RT Accessory Holder has one or more slots. NO The RT Accessory Holder has no slots.
>RT Accessory Holder Slot Sequence | (300A,0610) | 1C | Slots being available in this Accessory Holder. Required if RT Radiation Physical and Geometric Content Detail Flag (300A,0638) equals FULL and RT Accessory Holder Slot Existence Flag (300A,060F) has the value YES.. May be present if RT Accessory Holder Slot Existence Flag (300A,060F) has the value YES. One or more Items shall be included in this Sequence.
>>RT Accessory Holder Slot ID | (300A,0611) | 1 | The ID of the slot where accessories are inserted.
>>RT Accessory Holder Slot Distance | (300A,0612) | 2 | Distance in mm from the reference location as specified by RT Device Distance Reference Location Code Sequence (300A,0659) to the slot along the radiation beam axis.

###### C.36.2.2.14.1 RT Accessory Holders Description

In addition to RT Accessory Device Slots that are mounted directly on the treatment delivery unit, a treatment delivery unit may also allow the attachment of one or more accessory holders within which the user may install various devices for applying the beam to the patient, see Section C.36.2.2.3.1. Treatment accessory devices may include, but not be limited to, one or more of the following items:

- custom blocks on a block tray for patient-specific lateral collimation (beam limiting),

- pre-collimators for general lateral collimation (beam limiting),

- uniform thickness range shifter for modifying the range uniformly across the beam,

- two-dimensional range shifters (custom boluses) for modifying the range differentially across the defined field,

- ridge filters for creating multiple ranges within the beam,

- cross-wires for aligning the patient with the beam,

- a mirror or camera for aligning or viewing the irradiated area,

- beam monitoring detectors,

- applicator sealer for preventing fluids from entering the applicator.

The following example illustrates the use of the RT Accessory Holders Macro and the RT Accessory Device Identification Macro:

- The gantry head has an RT Accessory Device Slot ID called Acc Mount.

- In this example, an electron applicator is mounted in that RT Accessory Device Slot. The electron applicator itself has an RT Accessory Holder Slot called E Aperture, where other accessories can be mounted. Therefore, the electron applicator is an RT Accessory Holder, which includes an RT Accessory Holder Slot Sequence (300A,06010) Item to model that RT Accessory Holder Slot, identified by an RT Accessory Holder Slot ID (300A,0611).

- In this example, a block tray is mounted in the E Aperture RT Accessory Holder Slot. The block tray can support blocks, therefore it is an RT Accessory Holder, but the RT Accessory Holder Slot Sequence (300A,0610) is absent in the block tray definition, since the tray has no RT Accessory Holder Slots.

- The block is an RT Accessory Device, which is mounted in the block tray.

Figure C.36.2.2.14.1-1. RT Accessory Holders

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DICOM PS3.3 2021d - Information Object Definitions