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) 6/29/2020 1

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  6/29/2020 2

Requirements  Removes requirement to define characteristics by Irradiation Event  Define geometry  Use frame of reference (FOR) for complete beam description 6/29/2020 3

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. 6/29/2020 4

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  6/29/2020 5

Timing Example Real World Fluoroscopy DSA DSA CBCT Mode Static Rotating Gantry 1 2 3 4 5 6 7 Pedal Press Sample Encoding t 0 t end 1 2 3 4 5 6 7 Irradiation Event Complete Time Period 200 100 200 100 100 mA 500 mA Technique mA mA mA mA (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) Source Position 200 mGy 500 mGy 2 mGy 2 mGy 1 mGy 1 mGy 2 mGy 2 mGy 1 mGy 1 mGy Dose Output t

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 6/29/2020 7

Geometry +Y s Source +Z s - Position (x s , y s , z s ) = (0, 0, 0) +X s O s - Technique factors (potential, current, time) - Focal spot size ( ) - Anode material , , T T T - Inherent filtration x y z +X r +Z r Filtration (spectral filters, attenuating filters) O e - Position (x s , y s , z s ) - Dimensions +Y r - Material RDSR RCS - Thickness Attenuators (e.g., patient support, compression paddle) - Position (x r , y r , z r ) - Dimensions - Material 3.1 - Thickness 3.6 3.2 Radiation Output Information 2 - iAK at Point 2 (x s , y s , z s ) 3.5 Collimated field - Shape (x s , y s , z s ) (Points 3.1-6) 3.3 3.4 8

Transformation Matrix X-Ray Source Transformation Matrix       x M M M T x r 11 12 13 x s       RDS RDSR R Referenc ence e Sour urce e Coor oordi dinate te y M M M T y       Coordinate nate Syst ystem = System tem 12 22 23 r y s       z M M M T z ( ) = ( )  r   31 32 33 z   s  = P , , x y z P , , x y z       r r r r 1 0 0 0 1 1 s s s s P r P s +X s +Z r O e +Z s +X r ☢ O s +Y r +Y s RDSR RCS 9

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 6/29/2020 10

Rotating Sources v 1 = <0,0,1> + Θ v 2 = <0,-1,0> d cor = 500 mm DT Θ Center of v 1 Rotation DT 1 Θ 1 DT 2 Θ 2 d cor DT 3 Θ 3 +z r O e +x r DT 4 Θ 4 +y r v 2 … … T +x s +z s O s ☢         x x M M M T x 11 12 13 r s x s         +y s y y M M M T y         = = 12 22 23 r s y s T         z z M M M T z 31 32 33  r   s   z   s          1 1 0 0 0 1 1 6/29/2020 11

Rotating Sources + Θ + Θ Center of Rotation Center of v 1 v 1 Rotation d cor d cor v 2 v 2 +x s +z s +x s O s ☢ ☢ O s +y s +y s 6/29/2020 12

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  6/29/2020 13

Structure TID eRDSRT01 TID 1002 Observer TID eRDSRT05 Extended Radiation Context Radiation Source Dose Characteristics TID eRDSRT05B Radiation Technique TID 1204 Language of Content Item and Descendants TID eRDSRT06 TID eRDSRT13 Filtration Attenuator Characteristics TID eRDSRT07 TID eRDSRT13 TID eRDSRT02 Attenuators Attenuator Accumulated Dose Characteristics Data TID eRDSRT08 Radiation Output TID eRDSRT03 Irradiation Event TID eRDSRT09 Data Radiation Field Area TID eRDSRT10A X- TID eRDSRT04 Ray Source Irradiation Details Reference System TID eRDSRT10B Beam Position TID eRDSRT10C Attenuator Position TID eRDSRT11 Patient Attenuation Characteristics TID eRDSRT12 Procedure Characteristics 6/29/2020 14

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. 6/29/2020 15

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  6/29/2020 16