DICOM-RT: Coordinate system for radiotherapy systems DICOM-RT coordinate system

Background:

Following the previous blog post, continue to the science of cancer radiotherapy in the field of related concepts. The knowledge points in the article are from the relevant official or related enterprise documents, only from the perspective of the relevant industry practitioners, because I am not a radiotherapy doctor and technician, so may be different from the actual work of the link, welcome everyone to mail exchange, and common progress.
The beginning of this blog post let me start with the most familiar dicom file format, compared to ordinary BMP image, DCM is a combination of patients, hospitals, equipment and other related information on the pixel data above the file. But in terms of pixel data alone, there are also differences:

The standard BMP file pixel storage order is left to right, from bottom to top, that is, the coordinate origin is the lower left corner of the image, while DICOM standard storage order is from left to right, top to bottom, the coordinate origin is the upper left corner of the image. (see column for details dicom medical image processing: "Multiple BMP image data stored in DCM files" for DICOM storage operations)

This shows that the BMP image and DCM image coordinate system is different, in the course of tumor radiotherapy, there are several coordinate systems, see below for details:

The coordinate system in radiotherapy:

Radiation therapy involves patients, radiotherapy equipment (linear accelerator, collimator, leave shielding Gate MLC), consulting and other objects, there are different perspectives of the natural existence of a different coordinate system.

0. Default fixed coordinate system:

The coordinate system stipulated in IEC 61217 is "Cartesian right-hand coordinate system", the default horizontal axis (Xf) from left to right, the longitudinal axis (Yf) has front to rear, the vertical axis (Zf) from bottom to top. As shown in the following:

1. Patient Coordinate system:

The coordinate system in the DICOM standard is also derived from the IEC 61217 standard, the only difference being the patient coordinate system. Compared to the IEC patient coordinate system, the new patient coordinates of the DICOM standard (radiotherapy system) are the IEC patient coordinate system that rotates clockwise 90 degrees along the x axis.

2. Rack coordinate system (radial coordinate system):

In the course of radiotherapy, the main linear accelerator is the Ray generator. The so-called rack (gantry coordinate) coordinate system corresponds to the X-ray coordinate system (Beam coordinate).

Note: The patient coordinate system in is referred to as IEC Patient coordinate system
Let's look at an illustration in the Dicom standard, which is after the rack rotates 90 degrees clockwise:

The rotation of the rack system is YF clockwise along the fixed coordinate systems, as follows:

3. x-ray filter coordinate system:

The wedge Filter coordinate System is represented in the upper-right corner (XW,YW,ZW).

Note: s represents radiation Source;io representative isocenter;r/d F for radiation field or delineated radiation field

Radiotherapy Equipment Design diagram:

1. 1 representative rack (gantry) axis of rotation
2. 4 Rotary Shaft for beam limiter (collimator)
3. 5 for center rotation of patient support (IEC standard patient coordinate system)
4. 14 represents the distance from the radial field in the XF direction along the YF axis.
5. 15 represents the opposite of the XF axis to see the distance of the radial field in the YF direction.

If viewed from the top down (along the ZF reverse view) The above FX, FY is as follows:

Resources:

Http://dicom.nema.org/medical/dicom/current/output/chtml/part03/sect_C.8.8.25.6.html
Http://rtsafety.org/Download/Documents/CoordinateSystemsAndTransformations.pdf
Https://www.aapm.org/pubs/reports/OR_01.pdf

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Date: 2016-04-09

DICOM-RT: Coordinate system for radiotherapy systems DICOM-RT coordinate system