Supplement 214: Cone Beam CT RDSR SUPPLEMENT IS DEVELOPED BY DICOM - - PowerPoint PPT Presentation

Supplement 214: Cone Beam CT RDSR

SUPPLEMENT IS DEVELOPED BY DICOM WORKING GROUPS 02 AND 28 (WG-02 PROJECTION RADIOGRAPHY AND ANGIOGRAPHY) (WG-28 PHYSICS)

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Background

• Provide a framework that will allow for a more complete description of CBCT radiation
• In addition, much of the irradiation information is universal for all modalities
• The generation of radiation, filtration, and beam restriction of x-ray systems use similar, and in many

instances, identical methods

• Therefore, the proposal is to create an RDSR that does not require the modality to be

defined, and include existing modality-specific information when needed

• CBCT as a modality with specific requirements remains poorly defined
• Modalities are evolving, and new hybrid systems may be created
• Making a modality-agnostic RDSR will reduce or eliminate the need for CPs to accommodate new

technology or uses

• Legacy, regulatory, and other dose information from existing RDSRs can still be included
• This CBCT RDSR may allow for other modalities to take advantage of this generalizability

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Requirements

• Removes requirement to define characteristics by

Irradiation Event

• Define geometry
• Use frame of reference (FOR) for complete beam description

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Event Timing

• Current RDSR framework requires parameters to be described per irradiation event
• Limited methodology for describing parameters beyond an event
• Proposed RDSR framework describes a begin and end time of parameters
• Allows for describing radiation-dose-related characteristics of a system in two ways:
• Dependent solely on irradiation event
• For each irradiation event, describe the timing and all template content for each irradiation event individually
• Independent of irradiation events
• Parameter is characterized by a single value or table of values during specified period of time
• For characteristics that remain constant (or within some tolerance), create larger time periods that span

several irradiation events.

• For example, if the same technique is used across several irradiation events, the template can encode a

single template that indicates a constant technique across events

• For characteristics that change within an irradiation event, create smaller time periods that describe the

changes during the irradiation event

• For example, a rotating gantry during a CBCT run in XA can have many time windows that describe the

position of the gantry.

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Event Timing

• The methodology for beginning/ending the timing associated with a parameter is

implementation dependent

• Wait for a change in the characteristic to meet some threshold
• Percent change
• Absolute change
• Time dependent (every X seconds)
• By irradiation events
• All mandatory characteristics must be described completely for the entire time

spanned by each irradiation event

• There may be gaps between descriptions of parameters
• The information between irradiation events is not relevant for radiation dose

purposes.

• Characteristics may or may not be populated between irradiation events

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Sample Encoding Real World

Source Position

(0,0,10)

(-1,0,11) (-2,0,12) (-3,0,11) (-4,0,10) (-3,0,9) (-2,0,8) (-1,0,9) (0,0,10)

Dose Output

200 mGy 500 mGy

2 mGy 2 mGy 1 mGy 1 mGy 2 mGy 2 mGy 1 mGy 1 mGy

1 2 3 4 5 6 7

Irradiation Event Technique

100 mA 500 mA

200 mA 100 mA 200 mA 100 mA

Complete Time Period

t t0 tend

Fluoroscopy DSA DSA CBCT

Mode

1 2 3 4 5 6 7

Pedal Press Gantry

Static Rotating

Timing Example

Geometry

• A complete geometric description of all system components is required for a

complete understanding of dose distribution and potential patient impact

• Describing all components within a reference coordinate system improves

downstream users and systems to perform further dosimetry analysis

• Many radiographic systems have rotating sources
• Objects in the rotating frame of reference may not move in the rotating frame
• The proposed supplement uses a transformation matrix to relate a reference

coordinate system used by the system to a source coordinate system which may be moving

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Source

• Position (xs, ys, zs) = (0, 0, 0)
• Technique factors (potential, current, time)
• Focal spot size
• Anode material
• Inherent filtration

Collimated field

• Shape (xs, ys, zs) (Points 3.1-6)

RDSR RCS

Filtration (spectral filters, attenuating filters)

• Position (xs, ys, zs)
• Dimensions
• Material
• Thickness

Radiation Output Information

• iAK at Point 2 (xs, ys, zs)

2 3.1 3.6 3.4 3.3 3.2 3.5

Attenuators (e.g., patient support, compression paddle)

• Position (xr, yr, zr)
• Dimensions
• Material
• Thickness

Geometry

+Yr +Zr +Xr Oe +Ys +Zs +Xs Os

( )

, ,

x y z

T T T

8

Transformation Matrix

9

X-Ray Source Transformation Matrix

11 12 13 12 22 23 31 32 33

1 1 1

r x s r y s r z s

x M M M T x y M M M T y z M M M T z                   =                  

Sour urce e Coor

• ordi

dinate te System tem

☢

Ps

+Ys +Zs +Xs Os

( )

P , ,

s s s s

x y z =

RDS RDSR R Referenc ence e Coordinate nate Syst ystem

Pr

+Yr +Zr +Xr Oe

RDSR RCS

( )

P , ,

r r r r

x y z =

Rotating Source

• Rotating source descriptions can be simplified for many image acquisitions
• For sources rotating in a plane, a description of initial positioning within the coordinate

system, rotation radius, and rotation axis is sufficient to determine future positions and transformation matrices

• A simplified encoding scheme reduces the burden for implementation and relies on the

end user for calculation if desired

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Rotating Sources

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v1 = <0,0,1> v2 = <0,-1,0> dcor = 500 mm

DT Θ DT1 Θ1 DT2 Θ2 DT3 Θ3 DT4 Θ4 … … +yr +zr +xr Oe dcor v2

Center of Rotation

v1 +Θ

11 12 13 12 22 23 31 32 33

1 1 1 1

r s x s r s y s r s z s

x x M M M T x y y M M M T y z z M M M T z                         = =                         T T

+ys +zs +xs Os ☢

Rotating Sources

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dcor v2

Center of Rotation

v1 +Θ +ys +zs +xs Os ☢ dcor

Center of Rotation

v1 +Θ +ys +xs Os

☢

v2

Supplement Structure

• Creating templates that group related parameters can simplify the encoding

methodology and improve usability of the RDSR

• Items that change together can be updated together in the templates
• Related positions or machine characteristics are found in the same template

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Structure

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TID eRDSRT02 Accumulated Dose Data TID eRDSRT05 Radiation Source Characteristics TID eRDSRT06 Filtration TID eRDSRT07 Attenuators TID eRDSRT08 Radiation Output TID eRDSRT09 Radiation Field Area TID eRDSRT10B Beam Position TID eRDSRT04 Irradiation Details TID eRDSRT03 Irradiation Event Data TID eRDSRT11 Patient Attenuation Characteristics TID eRDSRT01 Extended Radiation Dose TID 1204 Language

• f Content Item and

Descendants TID 1002 Observer Context TID eRDSRT05B Radiation Technique TID eRDSRT10A X- Ray Source Reference System TID eRDSRT10C Attenuator Position TID eRDSRT12 Procedure Characteristics TID eRDSRT13 Attenuator Characteristics TID eRDSRT13 Attenuator Characteristics

Notes

• Promote mandatory technical information that allows the precise definition of needed

features of the system, e.g., the whole geometry and characteristics of the X-Ray beam, that are related to dose.

• Reduce constraints of mandatory “summary” radiation information.
• It is the role of regulators, not DICOM, to mandate of the presence of dose information
• These regulations are evolving (IEC, etc.), country-dependent, and they may mandate different

information depending on the “category” or “classification” of products within the same

• modality. Therefore, the manufacturers shall fill the information in the RDSR based on their

applicable regulations, case by case.

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Author Contacts

• Nicholas Bevins (editor)

nickb@rad.hfh.edu

• Heinz Blendinger

heinz.blendinger@t-online.de

• Steve Massey

steve.massey@pacshealth.com

• Donald Peck

donaldp@mtu.edu

• Francisco Sureda

francisco.sureda@med.ge.com

• Annalisa Trianni

annalisa.trianni@asufc.sanita.fvg.it

• DICOM Secretariat:

dicom@medicalimaging.org

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