Reference RT Structure Sets for Planar and Volumetric ROIs in DICOM SR TID 1500 Status August 2020 Voting Packet Date of Last Update 2020/07/04 Person Assigned David Clunie Submitter Name IDC Submission Date 2020/03/29 Correction Number CP-2035 Log Summary: Reference RT Structure Sets for Planar and Volumetric ROIs in DICOM SR TID 1500 Name of Standard PS3.16 Rationale for Correction: RT Structure Set (RTSS) objects are frequently used to define regions of interest (ROI) for radiation oncology. Rather than transcribing their 3D coordinates into an SR content item, it may be appropriate to reference an ROI within an RTSS object. This is possible, given the SR infrastructure, but not defined in the existing Planar and Volumetric templates. References to Conceptual Volumes defined for 2nd Generation RT are outside the scope of this CP, and may be the subject of a different CP. This CP is intended to address the installed base of RTSS producing systems and re-use of archives of RTSS objects. [Ed.Note. The SNOMED code (410673009, SCT, "Region") is not used, because its position in the class hierarchy as a child of (10546003, SCT, "Site") implies that it is an anatomical (body) region, not a generic region in space.] Correction Wording: This Template provides a general structure to report measurements for some metric, e.g., density, flow, or concentration, and/or qualitative evaluations, over a planar region of interest in an image. The ROI may be specified by an SCOORD on an image, by a Segmentation Image, or by an SCOORD3D defining an area relative to a 3D Frame of Reference, or by a reference to an ROI defined in a radiotherapy Structure Set.

Planar ROI Measurements and Qualitative Evaluations

	NL	Rel with Parent	VT	Concept Name	VM	Req Type	Condition	Value Set Constraint
1			CONTAINER	EV (125007, DCM, "Measurement Group")	1	M
...
5	>	CONTAINS	SCOORD	EV (111030, DCM, "Image Region")	1	MC	XOR Row 7, 7b, 8b	GRAPHIC TYPE = not {MULTIPOINT}
6	>>	SELECTED FROM	IMAGE		1	M
7	>	CONTAINS	IMAGE	EV (121214, DCM, "Referenced Segmentation Frame")	1	MC	XOR Row 5	Reference shall be to a Segmentation Image, with a single value specified in Referenced Frame Number, and with a single value specified in Referenced Segment Number
7b	>	CONTAINS	SCOORD3D	EV (111030, DCM, "Image Region")	1	MC	XOR Rows 5, 7, 8b	GRAPHIC TYPE = not {MULTIPOINT, POLYLINE or ELLIPSOID}
8	>	CONTAINS	IMAGE	EV (121233, DCM, "Source image for segmentation")	1	MC	IFF Row 7
8b	>	CONTAINS	COMPOSITE	EV (ddd001, DCM, "Region in Space")	1	MC	XOR Row 5, 7, 7b	Reference shall be to an RT Structure Set Storage SOP Class Instance.
8c	>>	HAS PROPERTIES	TEXT	EV (ddd002, DCM, "Referenced Region of Interest Identifier")	1	M		Reference shall be to a single value of ROI Number (3006,0022) within within an Item of Structure Set ROI Sequence (3006,0020) of the parent RT Structure Set Storage SOP Class Instance.
9	>	CONTAINS	IMAGE	EV (121200, DCM, "Illustration of ROI")	1	U
9b	>	CONTAINS	IMAGE	EV (130401, DCM, "Visual explanation")	1-n	U
...
13	>	CONTAINS	TEXT	$QualType	1-n	U

Content Item Descriptions Row 5 To describe an infinitely small area, such as the center of a lesion, a Graphic Type of POINT may be used. Rows 6, 7 Referenced Frame Number (0008,1160) is an attribute of the IMAGE Content Item, and shall be present with a single value. If the Referenced Segmentation SOP Instance has Segmentation Type (0062,0001) value BINARY, it identifies the area of defined (measured) region of interest by pixel values in the referenced frame with value 1. For Segmentation Type value FRACTIONAL, the area is computed by an implementation dependent method. Frame number shall be specified even if the Segmentation SOP Instance has only a single frame. Row 7b The area may be defined independently of an image by reference to 3D coordinates in any type of DICOM Reference Coordinate System, whether it be patient-relative (Patient Based Coordinate System), volume-relative (including acquired and presentation state volumes), or whole slide relative (Slide Coordinate System). Row 8 Identifies the source image that was segmented to identify the ROI, and whose properties are described in this container. Rows 8b, 8c A reference to a single ROI that defines a planar ROI, within an RT Structure Set. Row 9 This referenced image may contain a "screen shot" illustrating a rendered version of the ROI.

This Template provides a general structure to report measurements for some metric, e.g., density, flow, or concentration, and/or qualitative evaluations, over a volumetric region of interest in a set of images or a Frame of Reference. The volumetric ROI may be specified by a set of SCOORDs on an image set representing a volume, by a volumetric Segmentation Image, by a volume defined in a Surface Segmentation, or by a set of SCOORD3Ds defining a volume relative to a 3D Frame of Reference, or by a reference to an ROI defined in a radiotherapy Structure Set.

Volumetric ROI Measurements and Qualitative Evaluations

	NL	Rel with Parent	VT	Concept Name	VM	Req Type	Condition	Value Set Constraint
1			CONTAINER	EV (125007, DCM, "Measurement Group")	1	M
...
5	>	CONTAINS	SCOORD	EV (111030, DCM, "Image Region")	1-n	MC	XOR Rows 7, 10, 12b	GRAPHIC TYPE = not {MULTIPOINT}
6	>>	SELECTED FROM	IMAGE		1	M
7	>	CONTAINS	IMAGE	EV (121191, DCM, "Referenced Segment")	1	MC	XOR Rows 5, 10, 12b	Reference shall be to a Segmentation Image or Surface Segmentation object, with a single value specified in Referenced Segment Number
10	>	CONTAINS	SCOORD3D	EV (121231, DCM, "Volume Surface")	1-n	MC	XOR Rows 5, 7, 12b	If one item, GRAPHIC TYPE = {ELLIPSOID or POINT} If more than one item, GRAPHIC TYPE = {POLYGON or ELLIPSE}
11	>	CONTAINS	IMAGE	EV (121233, DCM, "Source image for segmentation")	1-n	MC	XOR Row 12 and IFF (Row 7 or Row 10)
12	>	CONTAINS	UIDREF	EV (121232, DCM, "Source series for segmentation")	1	MC	XOR Row 11 and IFF ((Row 7 or Row 10)
12b	>	CONTAINS	COMPOSITE	EV (ddd001, DCM, "Region in Space")	1	MC	XOR Row 5, 7, 10	Reference shall be to an RT Structure Set Storage SOP Class Instance.
12c	>>	HAS PROPERTIES	TEXT	EV (ddd002, DCM, "Referenced Region of Interest Identifier")	1	M		Reference shall be to a single value of ROI Number (3006,0022) within within an Item of Structure Set ROI Sequence (3006,0020) of the parent RT Structure Set Storage SOP Class Instance.
13	>	CONTAINS	IMAGE	EV (121200, DCM, "Illustration of ROI")	1-n	U
...

Content Item Descriptions Rows 5, 10 To describe an infinitely small volume, such as the center of a lesion, a Graphic Type of POINT may be used. Rows 6, 7 Referenced Segment Number (0062,000B) is an attribute of the IMAGE Content Item, and shall be present with a single value. If the Referenced SOP Instance is a Segmentation Image, it shall have a defined Frame of Reference. If it has Segmentation Type (0062,0001) value BINARY, it identifies the volume of defined (measured) region of interest by voxel values in the referenced segment with value 1. If it has Segmentation Type value FRACTIONAL, the volume is defined by an implementation dependent method. If the referenced SOP Instance is a Surface Segmentation, the referenced segment shall constitute a finite volume. It identifies the volume of the defined (measured) region of interest by the interior of the finite volume. Segment number shall be specified even if the Segmentation SOP Instance has only a single segment. Row 10 Either a single item describing a closed volumetric surface, or multiple items describing a set of parallel closed coplanar areas (contours) is specified. Row 11 Identifies the source images that were segmented to identify the ROI, when, for example a subset of images in a series was used. Row 12 Identifies the source series of images that were segmented to identify the ROI, when, for example an entire set of images in a series was used. Rows 12b, 12c A reference to a single ROI that defines a volumetric ROI, within an RT Structure Set. Row 13 These referenced images may contain "screen shot" illustrating rendered versions of the ROI.

Add new codes to PS3.16 Annex D:

DICOM Controlled Terminology Definitions (Coding Scheme Designator "DCM" Coding Scheme Version "01")

Code Value	Code Meaning	Definition	Notes
ddd001	Region in Space	A continuous part of space, not necessarily associated with a particular image.
ddd002	Referenced Region of Interest Identifier	A reference to an identifier of a Region of Interest. For example, a reference to the ROI Number (3006,0022) within an Item of Structure Set ROI Sequence (3006,0020) of an RT Structure Set Storage SOP Class Instance.

For reference unchanged, PS3.3:

A structure set defines a set of areas of significance. Each area can be associated with a Frame of Reference and zero or more images. Information that can be transferred with each region of interest (ROI) includes geometrical and display parameters, and generation technique.

Structure Set Module Attributes

Attribute Name	Tag	Type	Attribute Description
Structure Set Label	(3006,0002)	1	User-defined label for Structure Set.
Structure Set Name	(3006,0004)	3	User-defined name for Structure Set.
Structure Set Description	(3006,0006)	3	User-defined description for Structure Set.
Instance Number	(0020,0013)	3	A number that identifies this object Instance.
Structure Set Date	(3006,0008)	2	Date at which Structure Set was last modified.
Structure Set Time	(3006,0009)	2	Time at which Structure Set was last modified.
Referenced Frame of Reference Sequence	(3006,0010)	3	Sequence describing Frames of Reference in which the ROIs are defined. One or more Items are permitted in this Sequence. See .
>Frame of Reference UID	(0020,0052)	1	Uniquely identifies Frame of Reference within Structure Set.
>RT Referenced Study Sequence	(3006,0012)	3	Sequence of Studies containing Series to be referenced. One or more Items are permitted in this Sequence. See .
>>Include
>>RT Referenced Series Sequence	(3006,0014)	1	Sequence describing Series of images within the referenced Study that are used in defining the Structure Set. One or more Items shall be included in this Sequence.
>>>Series Instance UID	(0020,000E)	1	Unique identifier for the Series containing the images.
>>>Contour Image Sequence	(3006,0016)	1	Sequence of Items describing images in a given Series used in defining the Structure Set (typically CT or MR images). One or more Items shall be included in this Sequence.
>>>>Include
Structure Set ROI Sequence	(3006,0020)	1	ROIs for current Structure Set. One or more Items shall be included in this Sequence.
>ROI Number	(3006,0022)	1	Identification number of the ROI. The value of ROI Number (3006,0022) shall be unique within the Structure Set in which it is created.
>Referenced Frame of Reference UID	(3006,0024)	1	Uniquely identifies Frame of Reference in which ROI is defined, specified by Frame of Reference UID (0020,0052) in Referenced Frame of Reference Sequence (3006,0010).
>ROI Name	(3006,0026)	2	User-defined name for ROI.
>ROI Description	(3006,0028)	3	User-defined description for ROI.
>ROI Volume	(3006,002C)	3	Volume of ROI (cubic centimeters).
>ROI Generation Algorithm	(3006,0036)	2	Type of algorithm used to generate ROI. AUTOMATIC calculated ROI SEMIAUTOMATIC ROI calculated with user assistance MANUAL user-entered ROI
>ROI Generation Description	(3006,0038)	3	User-defined description of technique used to generate ROI.
>ROI Derivation Algorithm Identification Sequence	(3006,0037)	3	Software algorithm that derived the ROI. Only a single Item is permitted in this Sequence.
>>Include .
>Derivation Code Sequence	(0008,9215)	3	A coded description of how this ROI was derived. One or more Items are permitted in this Sequence. See for further explanation.
>>Include .			Enumerated Value (113085, DCM, "Spatial resampling").
>Definition Source Sequence	(0008,1156)	3	Instances containing the source of the ROI Contour information. Only a single Item is permitted in this Sequence.
>>Include .
>>Referenced Segment Number	(0062,000B)	1C	The value of Segment Number (0062,0004) in the referenced SOP Instance that identifies the segment that is the source of the ROI Contour information. Required if Referenced SOP Class UID (0008,1150) is Segmentation Storage ("1.2.840.10008.5.1.4.1.1.66.4").
>>Referenced Fiducial UID	(0070,031B)	1C	The value of Fiducials UID (0070,031A) in the referenced SOP Instance that identifies the fiducial that is the source of the ROI Contour information. Required if Referenced SOP Class UID (0008,1150) is Spatial Fiducials Storage ("1.2.840.10008.5.1.4.1.1.66.2").
Predecessor Structure Set Sequence	(3006,0018)	3	The Structure Set that has been used to derive the current Structure Set. Only a single Item is permitted in this Sequence.
>Include

The Referenced Frame of Reference Sequence (3006,0010) describes a set of frames of reference in which some or all of the ROIs are expressed. Since the Referenced Frame of Reference UID (3006,0024) is required for each ROI, each Frame of Reference used to express the coordinates of an ROI shall be listed in the Referenced Frame of Reference Sequence (3006,0010) once and only once. As an example, a set of ROIs defined using a single image Series would list the image Series in a single Referenced Frame of Reference Sequence (3006,0010) Item, providing the UID for this referenced Frame of Reference (obtained from the source images), and listing all pertinent images in the Contour Image Sequence (3006,0016).

Retired. See PS3.3-2011. The concept of definition of registered Frame of References using the Frame of Reference Relationship Sequence (3006,00C0) formerly present in the Standard is retired. The use of Registration IODs is advised since the introduction of Spatial Registration IOD, which is a much stronger and more general concept, and independent from the specifics of RT Structure Sets. Additionally it is of importance that registrations are decoupled from image and segmentation objects.

If an ROI is created by re-sampling an existing ROI that is either (a) present in a different Frame of Reference (FoR) and has been resampled to align with the image Series referenced by the current structure set, or (b) present in the same FoR, but its contours are referenced to a different image Series, it is useful to be able to identify that the ROI is resampled. The Derivation Code Sequence (0008,9215) shall be used with code (113085, DCM, "Spatial resampling") to indicate the resampled ROI.

Since RT Referenced Study Sequence (3006,0012) is Type 3, the Attribute may be omitted. If RT Referenced Study Sequence (3006,0012) is present with an Item, the SOP Class UID of the Detached Study Management SOP Class (Retired) may be used in Referenced SOP Class UID (0008,1150).

In general, a ROI can be defined by either a sequence of overlays or a sequence of contours. This Module, if present, is used to define the ROI as a set of contours. Each ROI contains a sequence of one or more contours, where a contour is either a single point (for a point ROI) or more than one point (representing an open or closed polygon).

ROI Contour Module Attributes

Attribute Name	Tag	Type	Attribute Description
ROI Contour Sequence	(3006,0039)	1	Sequence of Contour Sequences defining ROIs. One or more Items shall be included in this Sequence.
>Referenced ROI Number	(3006,0084)	1	Uniquely identifies the referenced ROI described in the Structure Set ROI Sequence (3006,0020).
>ROI Display Color	(3006,002A)	3	RGB triplet color representation for ROI, specified using the range 0-255.
>Recommended Display Grayscale Value	(0062,000C)	3	A default single gray unsigned value in which it is recommended that the contour be rendered on a monochrome display. The units are specified in P-Values from a minimum of 0000H (black) up to a maximum of FFFFH (white). The maximum P-Value for this Attribute may be different from the maximum P-Value from the output of the Presentation LUT, which may be less than 16 bits in depth.
>Recommended Display CIELab Value	(0062,000D)	3	A default triplet value in which it is recommended that the contour be rendered on a color display. The units are specified in PCS-Values, and the value is encoded as CIELab. See .
>Contour Sequence	(3006,0040)	3	Sequence of Contours defining ROI. One or more Items are permitted in this Sequence.
>>Contour Number	(3006,0048)	3	Identification number of the contour. The value of Contour Number (3006,0048) shall be unique within the Contour Sequence (3006,0040) in which it is defined. No semantics or ordering shall be inferred from this Attribute.
>>Attached Contours	(3006,0049)	3	List of Contour Number (3006,0048) defining lower-numbered contour(s) to which the current contour is connected.
>>Contour Image Sequence	(3006,0016)	3	Sequence of images containing the contour. One or more Items are permitted in this Sequence.
>>>Include
>>Contour Geometric Type	(3006,0042)	1	Geometric type of contour. See . POINT single point OPEN_PLANAR open contour containing coplanar points OPEN_NONPLANAR open contour containing non-coplanar points CLOSED_PLANAR closed contour (polygon) containing coplanar points
>>Contour Slab Thickness	(3006,0044)	3	Thickness of slab (in mm) represented by contour, where Contour Data (3006,0050) defines a plane in the center of the slab, offset by the Contour Offset Vector (3006,0045) if it is present. See .
>>Contour Offset Vector	(3006,0045)	3	Vector (x,y,z) in the Patient-Based Coordinate System described in that is normal to plane of Contour Data (3006,0050), describing direction and magnitude of the offset (in mm) of each point of the central plane of a contour slab from the corresponding original point of Contour Data (3006,0050). See .
>>Number of Contour Points	(3006,0046)	1	Number of points (triplets) in Contour Data (3006,0050).
>>Contour Data	(3006,0050)	1	Sequence of (x,y,z) triplets defining a contour in the Patient-Based Coordinate System described in (mm). See and . Contour Data may not be properly encoded if Explicit VR Transfer Syntax is used and the VL of this Attribute exceeds 65534 bytes.

A contour can be one of the following geometric types: A Contour Geometric Type (3006,0042) of POINT indicates that the contour is a single point, defining a specific location of significance. A Contour Geometric Type (3006,0042) of OPEN_PLANAR indicates that the last vertex shall not be connected to the first point, and that all points in Contour Data (3006,0050) shall be coplanar. A Contour Geometric Type (3006,0042) of OPEN_NONPLANAR indicates that the last vertex shall not be connected to the first point, and that the points in Contour Data (3006,0050) may be non-coplanar. Contours having a Geometric Type (3006,0042) of OPEN_NONPLANAR can be used to represent objects best described by a single, possibly non-coplanar curve, such as a brachytherapy applicator. A Contour Geometric Type (3006,0042) of CLOSED_PLANAR indicates that the last point shall be connected to the first point, where the first point is not repeated in Contour Data (3006,0050). All points in Contour Data (3006,0050) shall be coplanar.

A set of Contour slabs may define a multi-slab Volume of Interest. Contour Slab Thickness (3006,0044) shall specify the thickness of a slab, the central plane of which shall be defined by the set of points offset from Contour Data (3006,0050) by the value of Contour Offset Vector (3006,0045). One contour slab may contain one to many sets of Contour Data (3006,0050) that may define regions of one complex Volume of Interest. If no valid value of Contour Slab Thickness (3006,0044) is present, then the offset value shall be (0,0,0) and the original Contour Data (3006,0050) shall define the central plane of the Contour slab.

When a single ROI describes an excluded inner volume, this can be encoded with a single contour, using a "keyhole" technique. In this method, an arbitrarily narrow channel is used to connect the outer contour to the inner contour, so that it is drawn as a single contour. An example of such a structure is shown in Points in space lying along the path defined by the contour are considered to be inside the ROI.

RT Dose ROI provides ancillary dose-related information to the ROI data defined within the and , which may be included in the composite object. These Modules in combination provide for the definition of dose data in the form of isodose curves or named or unnamed dose points. Isodose curves in radiation oncology are simply contours identifying a set of points with the same dose value.

RT Dose ROI Module Attributes

Attribute Name	Tag	Type	Attribute Description
RT Dose ROI Sequence	(3004,0010)	1	Sequence specifying dose levels for isodose curves or dose points described in the ROI Module. One or more Items shall be included in this Sequence. See .
>Referenced ROI Number	(3006,0084)	1	Uniquely identifies the referenced ROI within the current RT Dose. See Note 1 and .
>Dose Units	(3004,0002)	1	Units used for ROI Dose. GY Gray RELATIVE dose relative to implicit reference value
>Dose Value	(3004,0012)	1	Dose value for ROI, in units defined by Dose Units (3004,0002). See .

The Structure Set ROI Sequence (3006,0020) defining the dose point and surfaces is defined in the . ROI Number (3006,0022) is unique within the Structure Set ROI Sequence, and is referenced from the using Referenced ROI Number (3006,0084). The defines the Attributes that describe references to ROIs contained within the associated and . Note that the RT Dose IOD Module table specifies that either all or none of the , , and must be present in the .

ROIs referenced in the shall have a Contour Geometric Type (3006,0042) of POINT, OPEN_PLANAR or CLOSED_PLANAR.

There shall be a one-to-one correspondence between Referenced ROI Number (3006,0084) and the Sequence of ROIs defined in the and . The shall only contain references to structures that are dose-related (i.e., dose points and isodose curves).

Dose Value (3004,0012) shall be the dose value corresponding to the referenced isodose curve, named dose point, or unnamed dose point.

The RT ROI Observations Module specifies the identification and interpretation of an ROI specified in the and .

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. SAME ROIs represent the same entity ENCLOSED referenced ROI completely encloses referencing ROI ENCLOSING referencing ROI completely encloses referenced ROI
>Include			May not be necessary if the anatomy is implicit in the RT ROI Identification Code Sequence (3006,0086). More than one item in Anatomic Region Sequence (0008,2218) may be used when a region of interest spans multiple anatomical locations and there is not a single pre-coordinated code describing the combination of locations. There is no requirement that the multiple locations be contiguous.
>Segmented Property Category Code Sequence	(0062,0003)	3	Sequence defining the general category of the property this ROI represents. Only a single Item is permitted in this Sequence. See Note .
>>Include			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 .
>>Include			For dose measurement devices Baseline . No Baseline CID is defined otherwise.
>>Segmented Property Type Modifier Code Sequence	(0062,0011)	3	Sequence defining the modifier of the property type of this segment. One or more Items are permitted in this Sequence.
>>>Include			D.
>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 . EXTERNAL external patient contour PTV Planning Target Volume (as defined in ) CTV Clinical Target Volume (as defined in ) GTV Gross Tumor Volume (as defined in ) TREATED_VOLUME Treated Volume (as defined in ) IRRAD_VOLUME Irradiated Volume (as defined in ) 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 DOSE_MEASUREMENT ROI representing a dose measurement device, such as a chamber or TLD
>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). 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 ratio of linear stopping power of material relative to linear stopping power of water ELEM_FRACTION elemental composition of the material MEAN_EXCI_ENERGY Mean Excitation Energy of the material (eV)
>>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 present.
>>>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 present. The sum of all ROI Elemental Composition Atomic Mass Fractions (3006,00B8) within 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. 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.

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. 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).

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).

Retired. See DICOM PS3.3 2016c.