DICOM-RT: Various images in the field of radiotherapy

Background:

The DICOM-RT Series blog focuses on the complementary criteria for radiotherapy in the DICOM3.0, namely Dicom-rt. In order to facilitate the follow-up on the dicom-rt of the relevant IoD, SOP concept of understanding, the column has recently done radiation-related knowledge points of popularization.
PS: Of course, I am not a radiation professional, the concept of the text from foreign literature books, Google, as well as wikis. The article is inappropriate, welcome everyone mail exchange.

Related images in the field of radiotherapy

Previous posts have briefly introduced the process of radiotherapy and related roles, as well as the development of radiotherapy programs, including target delineation, geometric planning, and dosage planning. There will be a variety of images. The following one by one lanes come:

1. CT from CT SIM

In the post DICOM-RT: The radiotherapy process and the role of the participants in the radiotherapy process, it is mentioned that the patient first needs to scan the constant-scale data, which refers to the conventional diagnostic CT scan (of course, it can also be an additional MRI, pet mode data). The following will also introduce the mode data of KV CBCT and MV CT, so the CT is limited to the three-dimensional image of CT simulator.
The CT Simulator is the diagnostic CT of the oncology department, which is the same as the CT spiral CT device in traditional radiology. The data collected is mainly used for the delineation of target areas by oncologists, and the development of radiotherapy programs for subsequent physiotherapists (dosimetry technicians). (Conventional CT can truly reflect the density of the substance, which may be used for dosage calculations, which are different from the CBCT image described below). Extract data from a set of targets in the 3DSlicer ( i.e. RT Structure set in Dicom-rt):

2. EPID (Electronic Portal Imaging Device)

Epid commonly known as the electron field image, the energy belongs to the mega-level ( that is, with the treatment of tumor treatment grade X-ray imaging, compared with conventional CT X-ray energy level ), mainly used for the treatment of images, position calibration and image guidance. The inherent disadvantage is that "the low contrast of the gigabit-grade radiographic image, the limited image acquisition range ", and the existing radiotherapy information system is mostly unable to integrate epid image . Epid with radiotherapy Accelerator, details are as follows:

Excerpt from: "Electronic Portal Imaging Devices:a Review and historical perspective of contemporary technologies and"
The image of Epid is collected before the patient is treated, and a planar two-dimensional graph of different angles obtained from several angles is taken, and a two-dimensional image reconstructed with the planned CT image (drr,digitally reconstructed radiographs, this is the RT Image in the Dicom-rt detailed in the following sectionThe alignment of the target is achieved by registration.

Excerpt from: "Dicom-rt and its utilization in radiation therapy"

3. KV-CBCT ( including flat film 2D, volume three and real-time perspective three images）

The KV grade CBCT, which gives the traditional medical linear accelerator volumetric imaging function, in the treatment of patients before the beginning of the treatment position, the CBCT image acquisition and reconstruction, to provide three-dimensional and soft tissue high-resolution volumetric imaging, to achieve more accurate target alignment.

4. MV-CBCT ( including flat film 2D, volume three and real-time perspective three images）

The CBCT, which uses linear accelerators directly as an imaging source of radiation , is good for imaging of tissues with high contrast (such as bones and lungs) or materials containing high atomic numbers such as dentures or hip implants. However, compared with KV-CBCT, the image quality of soft tissue is difficult to achieve the accuracy required by image guidance.

5. MV CT

Irradiation is carried out by a MV Linear accelerator on a ring-shaped frame, combined with the diagnostic helical ct slip ring technique , which is similar to a conventional helical CT scanner, and the linear accelerator can be rotated continuously around the patient. The fan beam modulated by the leave shielding grating can be applied to the patient's target area by layer intensity-modulated radiation therapy from any angle. But the MV CT images have their limitations, including the low contrast of soft tissue and the inefficient detector.
"Remarks":
A variety of imaging modes are mentioned above, where the amorphous silicon detector (Amfpis) used by CBCT is less expensive to manufacture and more resistant to radiation damage than the crystalline silicon technology for diagnostic-grade CT, Therefore, KV-CBCT and MV-CBCT can be used as the X-ray source directly using linear accelerators.
The standard diagnostic imaging uses an X-ray tube as a photon source, and the peak voltage is usually 70-120kvp. Compared to MV-class photons produced by linear accelerators, KV-level photons have a higher probability of interacting with irradiated targets, resulting in higher contrast images with lower radiation doses. Because the focus size of the X-ray ball tube is usually smaller than the linear accelerator, the spatial resolution of the KV image is higher than the MV image.
By integrating Kv-x and amfpis amorphous silicon detectors, they can be used for CBCT imaging, as well as for fluoroscopy and flat-sheet imaging.

Summarize

The various technologies have been updated to promote the development of radiotherapy, from the initial conventional two-dimensional radiotherapy, to three-dimensional conformal radiotherapy (3D-CRT), to intensity-modulated radiotherapy (IMRT), to imaging-guided radiotherapy (IGRT), to the final adaptive radiotherapy (ART). The only goal is to "faster, better and cheaper", to ensure targeted positioning, alignment, and image guidance, to reduce uncertainty in radiotherapy, which can occur between sub-treatments and can occur in each treatment.
By re-positioning or re-planning can control the difference between the treatment of the error, through the treatment of imaging monitoring of the structure of the body of the changes in the position, you can correct the error in each treatment. The image described above from the planning and actual radiation from the two points of view, can be CT Simulator diagnostic CT data classified as radiotherapy planning process, the rest of the many modal images (EPID, KV-CBCT, MV-CBCT, MV CT, etc.) are used in the treatment process of the target alignment and treatment monitoring.

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Date: 2016-04-13

DICOM-RT: Various images in the field of radiotherapy