Материал: part03

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differ from the Source to Surface Distance (300A,0130).​ See Section C.8.8.14.15.​

Note​

1.​Beam Number (300A,00C0) is provided to link related information across Modules, and its value should not be required​ to have any real-world interpretation. Beam Name (300A,00C2), a Type 3 Attribute, is intended to store the primary​ beam identifier (often referred to as "field identifier"). Beam Description (300A,00C3), a Type 3 Attribute, is intended to​ storeadditionalbeamidentifyinginformation(oftenreferredtoas"fieldname").EquipmentsupportingboththeseAttributes​ should state this clearly in the Conformance Statement.​

2.​The DICOM Standard does not support the transmission of treatment unit modeling information such as depth doses​ and beam profiles.​

3.​Implementers should take note that Leaf Position Boundaries (300A,00BE) are the positions of the mechanical bound-​ aries (projected to the isocentric plane) between beam limiting device (collimator) leaves, fixed for a given beam limiting​ device (collimator). Leaf/Jaw Positions (300A,011C) are values specific to a given beam control point, specifying the​ beam limiting device (collimator) leaf (element) openings.​

4.​Block coordinates may not be transmitted when such data is not available from the transmitting system. However, the​ receiving system may not have internal mechanisms to use or store such data. For example, a plan transmitted from​ an treatment planning system to a Record and Verify (R&V) system will contain the block data for blocked beams.​ Subsequent transfer of beam data from the R&V system may omit this data since the R&V system may not have stored​ it.​

5.​Refer to Section C.8.8.14.5 for examples of STATIC and DYNAMIC Beam Type. Note that beams having Wedge Type​ = DYNAMIC as the only moving parameter are not considered DYNAMIC according to the definition of Beam Type​ (300A,00C4).​

6.​Attributes Beam Dose Point Depth (300A,0088), Beam Dose Point Equivalent Depth (300A,0089), Beam Dose Point​ SSD(300A,008A)werepreviouslyincludedinthisModuleonthelevelofBeamSequence(300A,00B0)>ControlPoints​ BeamSequence(300A,0111)>ReferencedDoseReferenceSequence(300C,0050).TheseAttributeshavebeenretired​ at this location. See PS3.3-2011.​

C.8.8.14.1 Meterset Calculations​

TheMetersetatagivenControlPointisequaltoBeamMeterset(300A,0086)specifiedintheReferencedBeamSequence(300C,0004)​ of the RT Fraction Scheme Module, multiplied by the Cumulative Meterset Weight (300A,0134) for the Control Point, divided by the​ Final Cumulative Meterset Weight (300A,010E). The Meterset is specified in units defined by Primary Dosimeter Unit (300A,00B3).​ If the calculation for Meterset results in a Meterset value that is not an exact multiple of the primary Meterset resolution, then the​ resultshallberoundedtothenearestallowedMetersetvalue(i.e.,lessthanahalfresolutionunitshallberoundeddowntothenearest​ resolution unit, and equal or greater than half a resolution unit shall be rounded up to the nearest resolution unit).​

NotealsothatifFinalCumulativeMetersetWeight(300A,010E)isequalto100,thenCumulativeMetersetWeight(300A,0134)becomes​ equivalent to the percentage of Beam Meterset (300A,0086) delivered at each control point. If Final Cumulative Meterset Weight​ (300A,010E)isequaltoBeamMeterset(300A,0086),thentheCumulativeMetersetWeight(300A,0134)ateachcontrolpointbecomes​ equal to the cumulative Meterset delivered at that control point.​

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C.8.8.14.2 Planned Verification Image Sequence​

ThePlannedVerificationImageSequence(300A,00CA)containsAttributesthatdescribetheplannedverificationimagestobeacquired​ during current beam. The Start Cumulative Meterset Weight (300C,0008) specifies the Cumulative Meterset Weight at which image​ acquisition is to begin. If Meterset Exposure (3002,0032) is present in a Sequence Item and End Cumulative Meterset Weight​ (300C,0009) is not present then a single image shall be acquired using the Meterset duration specified in Meterset Exposure​ (3002,0032). If End Cumulative Meterset Weight (300C,0009) is present in a Sequence Item and Meterset Exposure (3002,0032) is​ not present then a single image shall be acquired over the beam delivery from Start Cumulative Meterset Weight (300C,0008) to End​ Cumulative Meterset Weight (300C,0009). If both Meterset Exposure (3002,0032) and End Cumulative Meterset Weight (300C,0009)​ are present in a Sequence Item then images shall be acquired every Meterset Exposure (3002,0032) from Start Cumulative Meterset​ Weight (300C,0008) to End Cumulative Meterset Weight (300C,0009). No images shall extend past End Cumulative Meterset Weight​ (300C,0009).​

C.8.8.14.3 X-Ray Image Receptor Angle​

TheX-RayImageReceptorAngle(3002,000E)specifiestherotationoftheimagereceptordeviceintheIECX-RAYIMAGERECEPTOR​ PLANE. A positive angle corresponds to a counter-clockwise rotation of the X-Ray Image Receptor as viewed from the radiation​ source in the IEC GANTRY coordinate system. The normal (non-rotated) value for this parameter is zero degrees.​

C.8.8.14.4 Multiple Aperture Blocks​

All blocks with Block Type (300A,00F8) of APERTURE for a given beam shall have equal values of Block Transmission (300A,0102)​ and/or Block Thickness (300A,0100) if they are specified. The composite aperture shall be evaluated as the union of the individual​ apertures within a single Block. Shielding block transmission(s) shall be applied multiplicatively after the (composite) aperture has​ been evaluated.​

C.8.8.14.5 Control Point Sequence​

The RT Beams Module uses a single beam model to handle static, arc, and dynamic delivery of external beam radiation by a medical​ accelerator or gamma beam therapy equipment (cobalt unit). All applicable parameters shall be specified at Control Point 0, with the​ exceptionofcouchpositions(seeSectionC.8.8.14.6).Allparametersthatchangeatanycontrolpointofagivenbeamshallbespecified​ explicitly at all control points (including those preceding the change). No assumptions are made about the behavior of machine​ parameters between specified control points, and communicating devices shall agree on this behavior outside the current Standard.​

The Cumulative Meterset Weight (300A,0134) values in a Control Point Sequence (300A,0111) shall be monotonically increasing in​ the order of increasing Control Point Index (300A,0112).​

Gantry Rotation Direction (300A,011F), Beam Limiting Device Rotation Direction (300A,0121), Patient Support Rotation Direction​ (300A,0123), and Table Top Eccentric Rotation Direction (300A,0126) are defined as applying to the segment following the control​ point, and changes to these parameters during treatment may be specified without use of a "non-irradiation" segment. All other​ ControlPointSequenceAttributesaredefinedonlyatthecontrolpoint.Tounambiguouslyencodechangesindiscrete-valuedAttributes​ such as Wedge Position (300A,0118) and Nominal Beam Energy (300A,0114), a non-irradiation segment where Cumulative Meterset​ Weight (300A,0134) does not change, shall be used.​

Some examples of beam specification using control points are as follows:​

a) Static delivery:​

Control Point 0: All applicable treatment parameters defined, Cumulative Meterset Weight = 0​

Control Point 1: Cumulative Meterset Weight = 1, no other parameters defined​

b) Arc delivery:​

Control Point 0: All applicable treatment parameters defined, Cumulative Meterset Weight = 0, Gantry Rotation Direction = rotation​ direction, Gantry Angle = initial angle​

Control Point 1: Cumulative Meterset Weight = 1, Gantry Rotation Direction = NONE, Gantry Angle = final angle​

c) Dynamic delivery of two equally weighted segments:​

Control Point 0: All applicable treatment parameters defined, Cumulative Meterset Weight = 0​

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Control Point 1: All changing treatment parameters defined (including those which do not change at this control point), Cumulative​ Meterset Weight = 0.5​

Control Point 2: All changing treatment parameters defined (including those which do not change at this control point), Cumulative​ Meterset Weight = 1​

d) Dynamic Delivery of two unequally weighted segments with a step change in table angle:​

Control Point 0: All applicable treatment parameters defined, Patient Support Angle = initial angle, Patient Support Rotation Direction​ = NONE, Cumulative Meterset Weight = 0​

ControlPoint1:Allchangingparametersdefined(includingthosethatdonotchangeatthiscontrolpoint),CumulativeMetersetWeight​ = 0.3, Patient Support Angle = initial angle, Patient Support Rotation Direction = rotation direction​

Control Point 2: All changing parameters defined (although none should change at this control point), Cumulative Meterset Weight =​ 0.3, Patient Support Angle = new angle, Patient Support Rotation Direction = NONE​

ControlPoint3:Allchangingparametersdefined(includingthosethatdonotchangeatthiscontrolpoint),CumulativeMetersetWeight​ = 1, Patient Support Angle = new angle, Patient Support Rotation Direction = NONE​

C.8.8.14.6 Absolute and Relative Machine Coordinates​

All treatment machine parameters except couch translations are specified in absolute machine coordinates as defined by IEC 61217.​ For the Table Top Vertical Position (300A,0128), Table Top Longitudinal Position (300A,0129), and Table Top Lateral Position​ (300A,012A), if the first Control Point contains a value of non-zero length, all subsequent Control Point position values are absolute​ valuesintheirrespectivecoordinatesystem.IfthefirstControlPointcontainsazero-lengthvalue,allsubsequentControlPointposition​ values are specified relative to the (unknown) initial value.​

C.8.8.14.7 Cumulative Dose Reference Coefficient​

The Cumulative Dose Reference Coefficient (300A,010C) is the value by which Beam Dose (300A,0084) is multiplied to obtain the​ dose to the referenced dose reference site at the current control point (and after previous control points have been successfully ad-​ ministered). The Cumulative Dose Reference Coefficient (300A,010C) is by definition zero for the initial control point. The Cumulative​ Dose Reference Coefficient (300A,010C) of the final control point multiplied by Beam Dose (300A,0084) results in the final dose to​ thereferenceddosereferencesiteforthecurrentbeam.Dosecalculationfordosereferencesitesotherthanpointsisnotwelldefined.​

C.8.8.14.8 Machine Rotations​

For the machine rotation angles Gantry Angle (300A,011E), Beam Limiting Device Angle (300A,0120), Patient Support Angle​ (300A,0122), and Table Top Eccentric Angle (300A,0125), rotation direction is specified as clockwise (CW), counter-clockwise (CC),​ or NONE. The maximum permitted rotation between two Control Points is 360 degrees. Examples:​

a.​Gantry Angle moves from 5 degrees to 5 degrees, Gantry Rotation Direction = NONE:​

No movement.​

b.​Gantry Angle moves from 5 degrees to 5 degrees, Gantry Rotation Direction = CW:​

Full clockwise rotation (360 degrees).​

c.​Table Angle moves from 170 degrees to 160 degrees, Table Rotation Direction = CC:​

Counter-clockwise rotation by 350 degrees (note direction of increasing table angle as defined by IEC 61217).​

C.8.8.14.9 Compensator Thickness Data and Source to Compensator Distance​

The values stored in Compensator Thickness Data (300A,00EC) and Source to Compensator Distance (300A,02E2) shall be parallel​ to the radiation beam axis if Compensator Divergence (300A,02E0) equals ABSENT, or divergent according to the beam geometrical​ divergence if Compensator Divergence (300A,02E0) equals PRESENT. If Compensator Divergence (300A,02E0) is not present, then​ the parallel or divergent nature of the thicknesses is as if ABSENT was specified for Compensator Divergence (300A,02E0).​

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