DICOM PS3.3 2021e - Information Object Definitions
C.36.2.3.2 RT Patient Position Macro

The RT Patient Position Macro defines a patient position in a treatment delivery or imaging session. This patient position may be specified as an absolute position of the patient positioning device or as relative displacement against a specified reference location.

The patient position may be based on recorded positions used in previous treatment sessions, or based on a position marked on the patient during a CT acquisition prior to treatment planning and delivery, or on other procedures.

The patient position approximates the desired patient position during radiation delivery. These Attributes do not affect the original spatial relationship between the RT Radiations and the planning image patient anatomy.

Table C.36.2.3.2-1. RT Patient Position Macro Attributes

Attribute Name

Tag

Type

Attribute Description

Include Table 10-15a “Patient Orientation And Equipment Relationship Macro Attributes”.

RT Patient Position Sequence

(300A,0799)

2C

Definition of patient position.

See C.36.2.3.2.1.1.

Required if RT Patient Position Displacement Sequence (300A,0798) is absent.

Zero or one Item shall be included in this Sequence.

>Include Table 10.39-1 “Patient to Equipment Relationship Macro Attributes”.

DCID 9553 “Treatment Points”.

RT Patient Position Displacement Sequence

(300A,0798)

2C

Displacement of the patient position.

See C.36.2.3.2.1.2.

Required if RT Patient Position Sequence (300A,0799) is absent.

Zero or one Item shall be included in this Sequence.

>Displacement Reference Label

(300A,079A)

3

A user-defined label describing the reference location used for a displacement of the patient’s treatment position.

>Displacement Reference Location Code Sequence

(300A,079D)

1

The reference location with respect to which the displacement is provided.

>>Include Table 8.8-1 “Code Sequence Macro Attributes”.

DCID 9574 “Patient Position Displacement Reference Points”.

>Conceptual Volume Sequence

(3010,0025)

2

References a Conceptual Volume that describes the geometry and properties of the Displacement Reference.

See C.36.2.2.16.1.1.

Zero or one Item shall be included in this Sequence.

>>Include Table 10.34-1 “Conceptual Volume Segmentation Reference And Combination Macro Attributes”.

>Displacement Matrix

(300A,079B)

1

A rigid, homogeneous 4x4 transformation matrix that expresses the patient’s treatment position displacement in the patient coordinate space. Matrix elements shall be listed in row-major order.

See C.36.2.3.2.1.2.

>Patient Support Displacement Sequence

(300A,079C)

2

evice-specific positioning parameters, derived from the Displacement Matrix (300A,079B).

See C.36.2.3.2.1.3.

Zero or one Item shall be included in this Sequence.

>>Include Table 10.40-1 “Patient Support Position Macro Attributes”.

DTID 15302 “Patient Support Position Parameters”.


C.36.2.3.2.1 RT Patient Position Macro Attribute Descriptions
C.36.2.3.2.1.1 RT Patient Position Sequences

This Sequence communicates a patient position as defined by the Image to Equipment Mapping Matrix (0028,9520) and may additionally contain native device parameters displayed to the user.

C.36.2.3.2.1.2 RT Patient Position Displacement Sequence

This Sequence communicates a patient position by specifying a displacement of the position with respect to a reference location. The reference location may be, for example, a set of skin markers used to align the patient using room lasers.

The Displacement Matrix (300A,079B) describes a relative displacement in the Patient Frame of Reference. The Patient Frame of Reference is aligned with the coordinate system of the patient support system (i.e., the axes are parallel). This specification is independent of the mechanical nature and readout of the patient support device. The calculation of the native parameters for the patient support system is specific to the current device.

C.36.2.3.2.1.3 Patient Support Displacement Sequence

The Displacement Matrix (300A,079B) is the exclusive source of information to define the displacement. Positioning devices will solely derive the displacement from this matrix.

Some applications, which do not act as positioning devices and cannot decompose the Displacement Matrix (300A,079B) into device-specific parameters, may want to informatively display device-specific parameters to the user. The purpose of the Patient Support Displacement Sequence (300A,079C) is to facilitate such display. The Patient Support Displacement Sequence (300A,079C) is not a substitute for the Displacement Matrix (300A,079B).

DICOM PS3.3 2021e - Information Object Definitions