C.8.8.3 RT Dose Module

The RT Dose module is used to convey 2D or 3D radiation dose data generated from treatment planning systems or similar devices. The attributes defined within the module support dose for a single radiation beam (potentially comprised of multiple segments, as delivered in a dynamic treatment) or a group of beams comprising either a fraction group (see C.8.8.13) or a complete treatment plan (potentially the sum of multiple fraction groups).

The RT Dose module provides the mechanism to transmit a 3D array of dose data as a set of 2D dose planes that may or may not be related to CT or MR image planes. This mechanism works via the DICOM Multi-Frame module which is required if multi-frame pixel data are sent.

Table C.8-39—RT DOSE MODULE ATTRIBUTES

Attribute Name Tag Type Attribute Description
Samples per Pixel (0028,0002) 1C Number of samples (planes) in this image. See C.8.8.3.4.1 for specialization. Required if Pixel Data (7FE0,0010) is present.
Photometric Interpretation (0028,0004) 1C Specifies the intended interpretation of the pixel data. See C.8.8.3.4.2 for specialization. Required if Pixel Data (7FE0,0010) is present.
Bits Allocated (0028,0100) 1C Number of bits allocated for each pixel sample. Each sample shall have the same number of bits allocated. See C.8.8.3.4.3 for specialization. Required Pixel Data (7FE0,0010) is present.
Bits Stored (0028,0101) 1C Number of bits stored for each pixel sample. Each sample shall have the same number of bits stored. See C.8.8.3.4.4 for specialization. Required if Pixel Data (7FE0,0010) is present.
High Bit (0028,0102) 1C Most significant bit for each pixel sample. Each sample shall have the same high bit. See C.8.8.3.4.5 for specialization. Required if Pixel Data (7FE0,0010) is present.
Pixel Representation (0028,0103) 1C Data representation of the pixel samples. Each sample shall have the same pixel representation. See C.8.8.3.4.6 for specialization. Required Pixel Data (7FE0,0010) is present.
Dose Units (3004,0002) 1 Units used to describe dose. Enumerated Values: GY = Gray RELATIVE = dose relative to implicit reference value
Dose Type (3004,0004) 1 Type of dose. Defined Terms: PHYSICAL = physical dose EFFECTIVE = physical dose after correction for biological effect using user-defined modeling technique ERROR = difference between desired and planned dose
Instance Number (0020,0013) 3 A number that identifies this object instance.
Dose Comment (3004,0006) 3 User-defined comments for dose data.
Normalization Point (3004,0008) 3 Coordinates (x, y, z) of normalization point in the patient based coordinate system described in C.7.6.2.1.1 (mm). See C.8.8.3.1.
Dose Summation Type (3004,000A) 1 Type of dose summation. Defined Terms: PLAN = dose calculated for entire RT Plan MULTI_PLAN = dose calculated for 2 or more RT Plans FRACTION = dose calculated for a single Fraction Group within RT Plan BEAM = dose calculated for one or more Beams within RT Plan BRACHY = dose calculated for one or more Brachy Application Setups within RT Plan CONTROL_POINT = dose calculated for one or more Control Points within a Beam
Referenced RT Plan Sequence (300C,0002) 1C Sequence describing RT Plan associated with dose. Required if Dose Summation Type (3004,000A) is PLAN, MULTI_PLAN, FRACTION, BEAM, BRACHY or CONTROL_POINT. Only a single item shall be included in this sequence, unless Dose Summation Type (3004,000A) is MULTI_PLAN, in which case two or more items shall be included in this sequence. See Note 1.
>Include ‘SOP Instance Reference Macro' Table 10-11
>Referenced Fraction Group Sequence (300C,0020) 1C Introduces sequence of one Fraction Group containing beams or brachy application setups contributing to dose. Required if Dose Summation Type (3004,000A) is FRACTION, BEAM, BRACHY or CONTROL_POINT. Only a single item shall be included in this sequence. See Note 1.
>>Referenced Fraction Group Number (300C,0022) 1 Uniquely identifies Fraction Group specified by Fraction Group Number (300A,0071) in Fraction Group Sequence of RT Fraction Scheme Module within RT Plan referenced in Referenced RT Plan Sequence (300C,0002).
>>Referenced Beam Sequence (300C,0004) 1C Introduces sequence of Beams in current Fraction Group contributing to dose. Required if Dose Summation Type (3004,000A) is BEAM or CONTROL_POINT. One or more items shall be included in this sequence.
>>>Referenced Beam Number (300C,0006) 1 Uniquely identifies Beam specified by Beam Number (300A,00C0) in Beam Sequence of RT Beams Module within RT Plan referenced in Referenced RT Plan Sequence (300C,0002).
>>>Referenced Control Point Sequence (300C,00F2) 1C Sequence defining the Control Points in current Beam contributing to dose. Required if Dose Summation Type (3004,000A) is CONTROL_POINT. Only a single item shall be included in this sequence.
>>>>Referenced Start Control Point Index (300C,00F4) 1 Identifies Control Point specified by Control Point Index (300A,0112) within Beam referenced by Referenced Beam Number (300C,0006). This is the first of the two Control Points from which the Dose contribution to the Control Point can be calculated.
>>>>Referenced Stop Control Point Index (300C,00F6) 1 Identifies Control Point specified by Control Point Index (300A,0112) within Beam referenced by Referenced Beam Number (300C,0006). This is the second of the two Control Points from which the Dose contribution to the Control Point can be calculated. The Control Point Index (300A,0112) referenced by Referenced Stop Control Point Index (300C,00F6) shall be the Control Point Index (300A,0112) immediately following the Control Point Index (300A,0112) referenced by Referenced Start Control Point Index (300C,00F4) within the Referenced Beam Number (300C,0006).
>>Referenced Brachy Application Setup Sequence (300C,000A) 1C Introduces sequence of Brachy Application Setups in current Fraction Group contributing to dose. Required if Dose Summation Type (3004,000A) is BRACHY. One or more items shall be included in this sequence.
>>>Referenced Brachy Application Setup Number (300C,000C) 1 Uniquely identifies Brachy Application Setup specified by Brachy Application Setup Number (300A,0234) in Brachy Application Setup Sequence (300A,0230) of RT Brachy Application Setups Module within RT Plan referenced in Referenced RT Plan Sequence (300C,0002).
Grid Frame Offset Vector (3004,000C) 1C An array which contains the dose image plane offsets (in mm) of the dose image frames in a multi-frame dose. Required if multi-frame pixel data are present and Frame Increment Pointer (0028,0009) points to Grid Frame Offset Vector (3004,000C). See C.8.8.3.2.
Dose Grid Scaling (3004,000E) 1C Scaling factor that when multiplied by the dose grid data found in the Pixel Data (7FE0,0010) attribute of the Image Pixel Module, yields grid doses in the dose units as specified by Dose Units (3004,0002). Required if Pixel Data (7FE0,0010) is present.
Tissue Heterogeneity Correction (3004,0014) 3 Specifies a list of patient heterogeneity characteristics used for calculating dose. This Atttibute shall be multi-valued if beams used to compute the dose have differing correction techniques. Enumerated Values: IMAGE = image data ROI_OVERRIDE = one or more ROI densities override image or water values where they exist WATER = entire volume treated as water equivalent

Note: In order to prevent misrepresentation of the dose summation:

  1. If the Dose Summation Type (3004, 000A) is PLAN, then only a single instance of RT Plan is referenced and the dose will be for the entire plan (i.e. it is not viable to combine only certain fraction groups of different plans).

  2. If the Dose Summation Type (3004,000A) is MULTI_PLAN, then 2 or more instances of RT Plan may be referenced. As above, each reference will be for the entire plan.

  3. If the Dose Summation Type (3004,000A) is FRACTION, then only a single instance of RT PLAN and a single Fraction Group are referenced (i.e. component beams or brachy application setups are not referenced).

C.8.8.3.1 Normalization Point

The Normalization Point (3004,0008) aids in the interpretation and subsequent use of the transmitted data. If used, it shall be a point receiving dose contributions from all referenced components of the dose summation.

C.8.8.3.2 Grid Frame Offset Vector

Grid Frame Offset Vector (3004,000C) shall be provided if a dose distribution is sent as a multi-frame image. Values of the Grid Frame Offset Vector (3004,000C) shall vary monotonically and are to be interpreted as follows:

a. If Grid Frame Offset Vector (3004,000C) is present and its first element is zero, this attribute contains an array of n elements indicating the plane location of the data in the right-handed image coordinate system, relative to the position of the first dose plane transmitted, i.e., the point at which the Image Position (Patient) (0020,0032) attribute is defined, with positive offsets in the direction of the cross product of the row and column directions.

b. If Grid Frame Offset Vector (3004,000C) is present, its first element is equal to the third element of Image Position (Patient) (0020,0032), and Image Orientation (Patient) (0020,0037) has the value (1,0,0,0,1,0), then Grid Frame Offset Vector contains an array of n elements indicating the plane location (patient z coordinate) of the data in the patient coordinate system.

In future implementations, use of option a) is strongly recommended.

This attribute is conditional since the RT Dose module may be included even if pixel doses are not being transmitted, or the image may be a single-frame image. If the Multi-frame Module is present, Frame Increment Pointer (0028,0009) shall have the Enumerated Value of 3004000C (Grid Frame Offset Vector).

Note: Option (a) can represent a rectangular-parallelepiped dose grid with any orientation with respect to the patient, while option (b) can only represent a rectangular-parallelepiped dose grid whose planes are in the transverse patient dimension and whose x- and y-axes are parallel to the patient x- and y-axes.

Example: Figure C.8.8.3-1 shows an example of plane positions for a dose grid with transverse planes.

[pic]

Figure C.8.8.3-1 Dose Grid Frame Example

For this example, Table C.8.39b gives the values of elements in the Grid Frame Offset Vector (3004,000C) for both relative (option (a)) and absolute (option (b)) interpretations, under the following conditions:

1. The value of Image Orientation (Patient) (0020,0037) is (1,0,0,0,1,0). I.e., the dose grid is transverse with x- and y-axes parallel to the patient x- and y-axes;

2. The value of Image Position (Patient) (0020,0032), i.e. the position of the first element of the dose grid, is (4, 5, 6); and

3. The spacing between adjacent dose grid planes is 2mm (uniform).

Table C.8-39b. Values of Dose Grid Frame Offset Vector underRelative (a) and Absolute (b) Interpretations

Grid Frame Offset Vector Element Option (a) Relative Coordinates Option (b) Absolute Coordinates
Z1 0 6
Z2 2 8
Z3 4 10
ZN 2(N-1) 6 + 2(N-1)

C.8.8.3.3 Dose Units

Dose Units are specified in both the RT Dose and RT Dose ROI modules. The attribute Dose Type present in the RT Dose module shall apply to all doses present in the RT Dose IOD.

C.8.8.3.4 Image Pixel Module Attributes

C.8.8.3.4.1 Samples per Pixel

For RT Doses, Samples per Pixel (0028,0002) shall have the Enumerated Value of 1.

C.8.8.3.4.2 Photometric Interpretation

For RT Doses, Photometric Interpretation (0028,0004) shall have the Enumerated Value of MONOCHROME2.

C.8.8.3.4.3 Bits Allocated

For RT Doses, Bits Allocated (0028,0100) shall have an Enumerated Value of 16 or 32.

C.8.8.3.4.4 Bits Stored

For RT Doses, Bits Stored (0028,0101) shall have an Enumerated Value equal to Bits Allocated (0028,0100).

C.8.8.3.4.5 High Bit

For RT Doses, High Bit (0028,0102) shall have the Enumerated Value of one less than the value sent in Bits Stored (0028,0101).

C.8.8.3.4.6 Pixel Representation

For RT Doses, Pixel Representation (0028,0103) is specified to use the following Enumerated Values:

0001H = two’s complement integer, when Dose Type (3004,0004) = ERROR

0000H = unsigned integer, otherwise.