C.8.8.8 RT ROI Observations Module
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#### C.8.8.8 RT ROI Observations Module

The RT ROI Observations module specifies the identification and interpretation of an ROI specified in the Structure Set and ROI Contour modules.

Table C.8-44. RT ROI Observations Module Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
RT ROI Observations Sequence | (3006,0080) | 1 | Sequence of observations related to ROIs defined in the ROI Module. One or more items shall be included in this sequence.
>Observation Number | (3006,0082) | 1 | Identification number of the Observation. The value of Observation Number (3006,0082) shall be unique within the RT ROI Observations Sequence (3006,0080).
>Referenced ROI Number | (3006,0084) | 1 | Uniquely identifies the referenced ROI described in the Structure Set ROI Sequence (3006,0020).
>ROI Observation Label | (3006,0085) | 3 | User-defined label for ROI Observation.
>ROI Observation Description | (3006,0088) | 3 | User-defined description for ROI Observation.
>RT Related ROI Sequence | (3006,0030) | 3 | Sequence of significantly related ROIs, e.g., CTVs contained within a PTV. One or more items are permitted in this sequence.
>>Referenced ROI Number | (3006,0084) | 1 | Uniquely identifies the related ROI described in the Structure Set ROI Sequence (3006,0020).
>>RT ROI Relationship | (3006,0033) | 3 | Relationship of referenced ROI with respect to referencing ROI. Defined Terms: SAME ROIs represent the same entity ENCLOSED referenced ROI completely encloses referencing ROI ENCLOSING referencing ROI completely encloses referenced ROI
>Segmented Property Category Code Sequence | (0062,0003) | 3 | Sequence defining the general category of this ROI. Only a single Item is permitted in this sequence. See Note 1.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | No Baseline CID is defined.
>RT ROI Identification Code Sequence | (3006,0086) | 3 | Sequence containing Code used to identify ROI. Only a single Item is permitted in this sequence. See Note 2.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | No Baseline CID is defined.
>Additional RT ROI Identification Code Sequence | (3006,00B9) | 3 | Sequence containing Code used to identify ROI for a particular purpose. One or more items may be present in this sequence. See Section C.8.8.8.2.
>>Include Table 8.8-1 “Code Sequence Macro Attributes” | No Baseline CID is defined.
>>Purpose of Reference Code Sequence | (0040,A170) | 1 | Describes the purpose for which the identification code is assigned. Only a single Item shall be permitted in this sequence.
>>>Include Table 8.8-1 “Code Sequence Macro Attributes” | No Baseline CID is defined. There shall be a private code scheme defined why there is an ROI identification code.
>Related RT ROI Observations Sequence | (3006,00A0) | 3 | Sequence of related ROI Observations. One or more items are permitted in this sequence.
>>Observation Number | (3006,0082) | 1 | Uniquely identifies a related ROI Observation.
>RT ROI Interpreted Type | (3006,00A4) | 2 | Type of ROI. See Section C.8.8.8.1. Defined Terms: EXTERNAL external patient contour PTV Planning Target Volume (as defined in ICRU50) CTV Clinical Target Volume (as defined in ICRU50) GTV Gross Tumor Volume (as defined in ICRU50) TREATED_VOLUME Treated Volume (as defined in ICRU50) IRRAD_VOLUME Irradiated Volume (as defined in ICRU50) BOLUS patient bolus to be used for external beam therapy AVOIDANCE region in which dose is to be minimized ORGAN patient organ MARKER patient marker or marker on a localizer REGISTRATION registration ROI ISOCENTER treatment isocenter to be used for external beam therapy CONTRAST_AGENT volume into which a contrast agent has been injected CAVITY patient anatomical cavity BRACHY_CHANNEL brachytherapy channel BRACHY_ACCESSORY brachytherapy accessory device BRACHY_SRC_APP brachytherapy source applicator BRACHY_CHNL_SHLD brachytherapy channel shield SUPPORT external patient support device FIXATION external patient fixation or immobilization device DOSE_REGION ROI to be used as a dose reference CONTROL ROI to be used in control of dose optimization and calculation
>ROI Interpreter | (3006,00A6) | 2 | Name of person performing the interpretation.
>Material ID | (300A,00E1) | 3 | User-supplied identifier for ROI material.
>ROI Physical Properties Sequence | (3006,00B0) | 3 | Sequence describing physical properties associated with current ROI interpretation. One or more items are permitted in this sequence.
>>ROI Physical Property | (3006,00B2) | 1 | Physical property specified by ROI Physical Property Value (3006,00B4). Defined Terms: REL_MASS_DENSITY mass density relative to water REL_ELEC_DENSITY electron density relative to water EFFECTIVE_Z effective atomic number EFF_Z_PER_A ratio of effective atomic number to mass (AMU-1) REL_STOP_RATIO linear stopping power ratio relative to water ELEM_FRACTION elemental composition of the material
>>ROI Elemental Composition Sequence | (3006,00B6) | 1C | The elemental composition of the ROI and the atomic mass fraction of the elements in the ROI. Required if ROI Physical Property (3006,00B2) equals ELEM_FRACTION. One or more items shall be included in this sequence.
>>>ROI Elemental Composition Atomic Number | (3006,00B7) | 1 | The atomic number of the element for which the ROI Elemental Composition Sequence (3006,00B6) is sent.
>>>ROI Elemental Composition Atomic Mass Fraction | (3006,00B8) | 1 | The fractional weight of the element for which the ROI Elemental Composition Sequence (3006,00B6) is sent. The sum of all ROI Elemental Composition Atomic Mass Fractions (3006,00B8) sent in the ROI Elemental Composition Sequence (3006,00B6) shall equal 1.0 within acceptable limits of floating point precision.
>>ROI Physical Property Value | (3006,00B4) | 1 | User-assigned value for physical property. ### Note The value has no meaning when ROI Physical Property (3006,00B2) has the value ELEM_FRACTION. Therefore this attribute may contain any value and receivers may ignore that value.

### Note

1. This attribute allows preserving information by copying the content of Segmented Property Category Code Sequence (0062,0003) in case a Segmentation object is re-encoded as an RT Structure Set or vice-versa.

2. In case of re-encoding a Segmentation object as an RT Structure Set or vice-versa it is suggested, that the Segmented Property Type Code Sequence (0062,000F) is mapped to RT ROI Identification Code Sequence (3006,0086).

##### C.8.8.8.1 RT ROI Interpreted Type

RT ROI Interpreted Type (3006,00A4) shall describe the class of ROI (e.g., CTV, PTV). Individual instances of each class of structure (e.g., CTV1, CTV2) can be distinguished using ROI Observation Label (3006,0085).

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C.8.8.7.3 Dose Value | Home | C.8.8.8.2 Additional RT ROI Identification Code Sequence