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The Referenced Defined Device Index (300A,0602) provides the facility to relate devices from one Instance to the other. Device Macros such as the RT Beam Limiting Device Definition Macro are used in Sequences which list the devices used in the context of a SOP Instance. Each device is identified by the Device Index (3010,0039). These devices may be described in other related SOP Instances. The values of Device Index (3010,0039) are not required to be the same in different SOP Instances.

For example, an RT Radiation Instance may contain the RT Beam Limiting Device Definition Sequence (300A,064D), listing the Beam Limiting Devices to be used for treatment. A related RT Radiation Record Instance for the same type of delivery device will contain the same Sequences. However, the collection of devices used may not be the same:

E.g., the RT Radiation Instance may describe a treatment that contains three Items with the following indices:

However, the treatment may have been executed on a different machine which has the X-Jaws and the X-MLC, but a fixed collimator in the Y direction instead of the Y-Jaws. Therefore, the Y-Jaws will not be recorded as they have not been used. Also, the fixed collimator in Y direction is not recorded, as this is not a device which is part of the RT Beam Limiting Device Definition Sequence (300A,064D). The Referenced Defined Device Index (300A,0602) will then point to the indices in the referenced RT Radiation Instance to annotate which device in the RT Radiation Record corresponds to the device in the RT Radiation. In this case, the RT Radiation Record would contain the devices as listed in the following: