Материал: part03

C.36.2.2.4 RT Treatment Position Macro​

The RT Treatment Position Macro establishes a connection between the patients geometry and the treatment delivery equipment to​ define the treatment position. When used in an RT Radiation object, this treatment position is the prescribed position. When used in​ an RT Radiation Record object, this treatment position is the record of the actual position.​

Table C.36.2.2.4-1. RT Treatment Position Macro Attributes​

C.36.2.2.5 RT Control Point General Macro​

This Macro specifies the base Attributes for the definition of an RT Radiation Control Point.​

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Table C.36.2.2.5-1. RT Control Point General Macro Attributes​

Required if the conditions in Section C.36.2.2.5.1.1 are satisfied.​

C.36.2.2.5.1 RT Control Point Attribute Concept​

The treatment-modality Modules use a common formalism to represent parameters that define the behaviour of a delivery device​ during delivery of radiation. These parameters are communicated as a sequence of values, organized as Control Points (see Sec-​ tion C.36.1.1.1) and represented as RT Control Points. The resolution of RT Control Points depends on the level of detail required to​ define the behaviour of the delivery device.​

A Control Point is a point on a timeline of a delivery process. RT Control Points are sequenced using an index number starting with​ 1, e.g., 1, 2, 3, 4. The RT Control Point parameters reflect the state of the delivery device at that point in time. The Control Point Cu-​ mulative Meterset reflects the dose that has been delivered from the beginning of the delivery process up to that point in time.​

For all beam deliveries there are at least two RT Control Points, corresponding to the start and end of delivery. E.g., for a simple​ Static Beam delivery with a constant field aperture, only two RT Control Points are needed to define the start and end, as there are​ no changes in-between. For a dynamic delivery, in which the MLC leaves are changing while radiation is delivered, the number of​ Control Points will be higher to provide enough detail to define the leaf movement with sufficient resolution to achieve the radiation​ fluence distribution expected for the prescribed dose.​

DICOM does not specify the behavior of the machine parameters between Control Points. The planning system needs to know the​ hardware-specific characteristics of the delivery system for which the plan is being created.​

C.36.2.2.5.1.1 Requirements for Changing Values within RT Control Point Sequence Attributes​

This Section specifies when individual attributes shall be present in a Sequence.​

The RT Control Point Sequence specifies a certain order of execution.​

At each RT Control Point the value of various Attributes may be specified as an explicit value (which in the case of a type 2C attribute​ may be a null value) and if absent remain at the same value as specified previously. There are physical and mechanical implications​ of specifying a new value as opposed to staying at the same value, for example gear lash, floating point jitter, etc.​

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At the first Sequence Item in RT Control Point Sequences (i.e., with an RT Control Point Index (300A,0600) equal to 1) all Attributes​ affected by this Section shall be present if applicable conditions are met.​

For Sequence Items other than the first Sequence Item, Attributes shall be present if applicable conditions are met and the value is​ different from the previously populated value for the same Attribute (in the case of a type 2C attribute, a null value is considered as​ a value). The previously populated value is the value from the Item where the Attribute was present with the greatest value of RT​ Control Point Index (300A,0600) less than the value of the RT Control Point Index (300A,0600) in the current Item.​

This means that for an Item in which an Attribute is absent, the application stays at the value of the previously populated Item.​

For Sequences inside a RT Control Point Sequence Item, the Sequence shall be present if any of the nested Attributes affected by​ this Section differ from the corresponding previously populated Item.​

Formulti-valuedAttributes,suchasParallelRTBeamDelimiterPositions(300A,064A),allvaluesshallbepresentifanyvaluechanges.​

C.36.2.2.5.1.2 Control Point Attribute Example​

The following examples illustrate RT Control Points:​

At completion this beam delivers 76 Monitor Units using a fixed static set of treatment parameters defined in RT Control Point 1.​

At completion this delivers 56 Monitor Units while rotating the gantry from initial angle to final angle.​

3.​Dynamic delivery of two equally weighted segments:​

At completion this delivers 80 Monitor Units while first increasing the Y opening and then increasing the X opening, while the​ beam limiting device angle stays fixed. For the RT Beam Limiting Device Opening Sequence (300A,0656) this results in having​ three Items for the first Control Point and only one for Control Points 2 (Referenced Device Index 2 only) and 3 (Referenced​ Device Index 1 only). See also Figure C.36.2.2.5.1-1.​

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Figure C.36.2.2.5.1-1. Control Points Sub-Sequence Attribute Presence​

4.​Dynamic Delivery of two unequally weighted segments with a step change of 5 degrees in the positive direction of the Patient​ Support Angle:​

Note​

Patient Support Angle is represented by the Image to Equipment Mapping Matrix (0028,9520). The table contains the​ effective angle and not the complete matrix.​

At completion this delivers 90 Monitor Units. Between RT Control Point 2 and 3 the Patient Support Angle and Source Roll​ Continuous Angle are changed and no radiation is delivered.​

C.36.2.2.5.1.3 Cumulative Meterset​

The Meterset at a given Control Point is specified by Cumulative Meterset (300A,063C). This value is specified in units defined by​ RadiationDosimeterUnitSequence(300A,0658)intheRTDeliveryDeviceCommonModuleinSectionC.36.12.TheMetersetvalues​ are intended to correspond to the values produced by the primary or the single Meterset-measuring device of a RT Radiation Delivery​ Device.​

C.36.2.2.6 External Beam Control Point General Macro​

This Macro specifies the RT Control Point Attributes used to model external beam radiation.​

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Table C.36.2.2.6-1. External Beam Control Point General Macro Attributes​

C.36.2.2.7 Radiation Generation Mode Macro​

The Radiation Generation Mode Macro contains Attributes required to generate radiation by a delivery device.​

Treatment devices can produce a multitude of different beams with properties such as energy spectrum, depth dose, surface dose​ and beam profile. A particular combination of such properties is referred to as a Radiation Generation Mode. Such Radiation Gener-​ ation Modes are created by the machine by using different primary electron/particle beams, flattening and scattering filters, etc., cre-​ atingaspecificphysicalandgeometricdistributionofradiation.InmanycasestheRadiationGenerationModecharacterizesthefluence​ just below the Monitor Chamber. Subsequently these primary beams may be modulated by beam modifiers such as Beam Limiting​ Devices, Wedges, Spreaders etc. While these beam modifiers are described in the Control Point Sequence, the primary beam is as-​ sumed to have fixed characteristics. In many cases, the Radiation Generation Mode will be constant throughout the radiation.​

Radiation Generation Modes specify the beam fluence. To convey content other than the beam fluence, such as annotating the role​ of the beam in the clinical process or the usage of that beam during a treatment session, annotate treatment constraints, use other​ AttributeslikeRTRadiationSetIntent(300A,0637)intheRTRadiationSetModuleandinformationprovidedbytheworkflowprotocols.​

Table C.36.2.2.7-1. Radiation Generation Mode Macro Attributes​

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