Radiation therapy with image guidance ( IGRT ) is a frequent two- and three-dimensional imaging process, during radiation treatment, used for direct radiation therapy using imaging coordinates of a radiation treatment plan in fact. Patients are localized in the treatment room in the same position as planned from the reference imaging dataset. An IGRT example will include the localization of a cone beam computed tomography (CBCT) dataset with computed tomography (CT) planning of the dataset of the plan. IGRT will also include planar kilovoltage (kV) or megavoltage (MV) radiographic images with digital reconstructed radiography (DRR) from planning CT. Both of these methods comprise most of the IGRT strategies currently in use around 2013.
This process differs from the use of imaging to describe targets and organs in the radiation therapy planning process. However, there is clearly a link between the imaging process because IGRT relies directly on the imaging modalities of planning as reference coordinates to localize the patient. Various medical imaging technologies used in the planning include x-ray computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) among others. IGRT accuracy is significantly improved when N-localizer technology is used in conjunction with this medical imaging technology. Through advances in imaging technology, combined with further understanding of human biology at the molecular level, the impact of IGRT on radiotherapy treatments continues to evolve.
Video Image-guided radiation therapy
Clinical goals and benefits
The purpose of the IGRT process is to improve the accuracy of radiation field placement, and to reduce exposure to healthy tissue during radiation treatment. In previous years, larger target volume planning margins (PTV) were used to compensate for localization errors during the treatment. This results in a healthy human tissue receiving unnecessary radiation doses during the treatment. PTV Margin is the most widely used method to take into account geometric uncertainty. By increasing accuracy through IGRT, radiation decreases to surrounding healthy tissue, allowing increased radiation to the tumor for control.
At present, certain radiation therapy techniques use the intensity-modulated radiotherapy (IMRT) process. This form of radiation treatment uses a computer and linear accelerator to sculpt a three-dimensional radiation dose map, specific to location characteristics, shape, and target movement. Because of the level of precision required for IMRT, detailed data should be collected on the location of the tumor. The single most important area of ​​innovation in clinical practice is the reduction of the target volume margin target around the site. The ability to avoid more normal tissue (and thus potentially using dose escalation strategies) is a direct byproduct of the ability to perform therapy with the highest accuracy.
Modern and advanced radiotherapy techniques such as proton and radiotherapy charged particles allow superior precision in dose delivery and spatial distribution of effective doses. At present, that possibility adds new challenges to IGRT, regarding the precision and reliability required. Therefore, an appropriate approach is an intensive research problem.
IGRT increases the amount of data collected during therapy. During this time, whether for an individual or patient population, this information will allow for continued assessment and further refinement of the treatment technique. The clinical benefit for patients is the ability to monitor and adapt to changes that may occur during radiation treatment. Such changes may include tumor shrinkage or expansion, or changes in the shape of the tumor and the surrounding anatomy.
Maps Image-guided radiation therapy
Rationale
Radiation therapy is a local treatment designed to treat a prescribed tumor and store the surrounding normal tissue from receiving a dose above a prescribed dose tolerance. There are many factors that can contribute to the difference between planned dose distribution and dose distribution. One such factor is the uncertainty in the patient's position in the treatment unit. IGRT is a component of the radiation therapy process that combines the drawing coordinates of the treatment plan to be delivered to ensure patients are properly placed in the treatment room.
Localization information provided through the IGRT approach can also be used to facilitate robust maintenance planning strategies and enable patient modeling, which is beyond the scope of this article.
History "guide" for care
Surface and skin mark
Generally, at the time of 'planning' (whether clinical mark up or full simulation) the areas intended for treatment are outlined by radiation oncologists. Once the treatment area is determined, the marks are placed on the skin. The purpose of the ink is to align and position the patient daily for treatment to improve the reproducibility of the placement. By aligning the signs with the radiation (or representative) field in the radiation therapy therapy room, correct placement of the treatment area can be identified.
Over time, with technological improvements - the field of light with cross hair, isocentric lasers - and with a shift to 'tattooing' - a procedure in which the ink marks are replaced by a permanent sign by applying the ink just below the first layer of skin using the needle at the documented location - reproducibility of patient settings improved.
Portal imagery
Portal imaging is the acquisition of images using the radiation beam used to provide radiation treatment to the patient. If not all radiation rays are absorbed or dispersed in the patient, passing portions can be measured and used to produce patient images.
It is difficult to establish the initial use of portal imaging to determine the placement of the radiation field. From the earliest days of radiation therapy, X-rays or gamma rays were used to develop large-format radiographic films for examination. With the introduction of the cobalt-60 machine in the 1950s, radiation went deeper into the body, but with low contrast and poor subjective visibility. Today, using advances in digital imaging devices, the use of electronic portal imaging has evolved into both a tool for accurate field placement and as a quality assurance tool for review by radiation oncologists during movie reviews.
Electronic portal imagery
Electronic portal imaging is the process of using digital imaging, such as CCD video cameras, ionic ion spaces and amorphous silicon flat panel detectors to create digital images with improved quality and contrast compared to traditional portal imaging. The benefits of this system are the ability to capture images, for review and guidance, digitally. This system is used throughout clinical practice. The current review of the Electronic Portal Imaging Device (EPID) shows acceptable results in irradiation imaging and in most clinical practice, providing a considerable field of view. kV is not a portal imaging feature.
Imaging for maintenance guides
Fluoroscopy
Fluoroscopy is an imaging technique that uses a fluoroscope, coordinating with a screen capture device or image to create a real-time image of the patient's internal structure.
Digital X-ray
Digital X-ray equipment installed in the radiation treatment device is often used to describe the patient's internal anatomy before or during treatment, which can then be compared with the initial planning CT series. The use of orthogonal set-up of two radiographic axes is common, to provide a means for highly accurate patient position verification.
Computed tomography (CT)
A medical imaging method uses tomography in which digital geometry processing is used to generate three-dimensional images of the internal structure of an object from a large set of two-dimensional X-ray images taken around a single rotation axis. CT produces a data volume, which can be manipulated, through a process known as windowing, to show the various structures based on their ability to attenuate and prevent the transmission of X-ray events.
Conventional CT
With the growing use of CT imaging in using guidance strategies to adjust the treatment volume position and placement of the treatment field, several systems have been designed that place the actual conventional 2-D CT machine in the treatment room along with linear accelerator treatment. The advantage is that conventional CT provides an accurate measure of network attenuation, which is important for dose calculations (eg CT on rails).
Beam cone
Cone-beam computed tomography (CBCT) based image guidance system has been integrated with a medical linear accelerator for great success. With the improvement of flat panel technology, CBCT has been able to provide volumetric imaging, and allows for the monitoring of radiographs or fluoroscopy during the treatment process. The CT beam cone obtains many projections of the entire volume of interest in each projection. Using the reconstruction strategy pioneered by Feldkamp, ​​2D projection is reconstructed into an analog 3D volume with a set of CT planning data.
MVCT
Megavoltage computed tomography (MVCT) is a medical imaging technique that uses the X-ray Megavoltage range to create images of bone structures or replacement structures in the body. The original truth for MVCT is driven by the need for accurate density estimates for treatment planning. Both the localization of the patient's structure and the target are secondary uses. A test unit uses a single linear detector, which consists of 75 cadmium tungstate crystals, mounted on a linear accelerator gantry. The test results show 0.5 mm spatial resolution, and 5% contrast resolution using this method. While other approaches may involve integrating the system directly into MLA, it will limit the number of revolutions to numbers prohibited for regular use.
Optical tracking
Optical tracking involves the use of cameras to relay the position information of objects in the coordinate system attached by means of a subset of the wavelength electromagnetic spectrum that includes ultraviolet, visible, and infrared light. Optical navigation has been used for the last 10 years in image guiding operations (neurosurgery, ENT, and orthopedics) and has increased prevalence in radiotherapy to provide real-time feedback through visual cues in the graphical user interface (GUI). For the latter, the calibration method is used to align the camera's original coordinate system with those in the isocentric reference framework of the radiation therapy delivery chamber. The optically tracked devices were then used to identify the position of patient reference setting points and this was compared to their location in the CT planning coordinate system. Calculations based on the least squares methodology were performed using two sets of coordinates to determine the treatment sofa translation that would result in the alignment of the planned isocenter of the patient with the treatment room. These tools can also be used for intra-fraction monitoring of the patient's position by placing a device tracked optically on an interesting region to initiate radiation delivery (ie gating regime) or action (ie repositioning). Alternatively, products such as AlignRT (from Vision RT) allow real-time feedback by directly imaging the patient and tracking the patient's skin surface.
MRI
The clinically active MRI-guided radiation therapy machine, ViewRay device, installed at St. Louis, MO, at the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine. The first patient care was announced in February 2014. Other radiation therapy machines incorporating MRI tumor tracking in real-time are under development. MRI-guided radiation therapy allows doctors to view the patient's internal anatomy in real-time using continuous soft tissue imaging and allows them to keep the radiation of the light on the target when the tumor moves during treatment.
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Ultrasound is used for everyday patient settings. This is useful for soft tissues such as breast and prostate. The BAT system (Best Nomo) and Clarity (Elekta) are the two main systems currently in use. The Clarity system has been further developed to enable intra-fraction prostate motion tracking through trans-perineal imaging.
Electromagnetic transponders
Although not IGRT per se, the electromagnetic transponder system strives to serve the exact same clinical functions as CBCT or X-ray kV, but provides a temporary, temporal analysis of analogue setting errors analogous to optical tracking strategies. Therefore, this technology (although using "images") is usually classified as an IGRT approach.
Correction strategy for positioning of patient during IGRT
There are two basic correction strategies used when determining the most favorable patient position and ray structure: on-line and off-line correction. Both serve their purpose in a clinical setting, and have their own advantages. Generally, a combination of both strategies is used. Often, a patient will receive a correction for their treatment through an on-line strategy during their first radiation session, and the doctor makes subsequent adjustments off-line during the movie round.
On-line
On-line strategies make adjustments to patients and beam positions during the treatment process, based on information that is constantly updated throughout the procedure. The on-line approach requires the integration of high level software and hardware. The advantage of this strategy is the reduction of both systematic and random errors. An example is the use of marker-based programs in the treatment of prostate cancer at Princess Margaret Hospital. Gold markers are implanted into the prostate to provide a gland replacement position. Prior to daily treatment, portal imaging system results are returned. If the mass center has moved larger than 3mm, then the sofa will be reset and the next reference image will be created. Another correct clinic for every position error, never allow & gt; 1 mm error in measured ax.
Off-line
Off-line strategy determines the best patient's position through the accumulation of data collected during the treatment sessions, almost always the initial treatment. Doctors and staff measure the accuracy of care and design treatment guidelines while using information from the image. Strategies require greater coordination than online strategies. However, the use of off-line strategies does not reduce the risk of systematic errors. However, the risk of random error still persists.
Future studies
- The debate between the benefits of on-line versus off-line strategies continues to be taken into account.
- Whether further research into biological function and movement can create a better understanding of tumor movements in the body before, between and during treatment.
- When rules or algorithms are used, large variations in the PTV margin can be reduced. The "recipe" margin is being developed which will create linear equations and algorithms that take into account "normal" variations. These rules are made from normal populations, and applied to off-line maintenance plans. Possible side effects include random errors of the target uniqueness
- With more data being collected, how the system should be set to categorize and store information.
See also
References
Further reading
- Cossmann, Peter H. Progress in Image Therapeutic Radiotherapy - The Future of Moves. European Oncology Review 2005 - July (2005)
- Sharpe, MB; T Craig; DJ Moseley (2007) [2007]. "Picture Guidance: Targeted Localization Targeting System at IMRT-IGRT-SBRT - Advances in Radiotherapy Treatment and Delivery Planning.". Limits in Radiation Therapy Oncology . 40 . Madison, WI: Karger. ISBN: 978-3-8055-8199-8.
Source of the article : Wikipedia
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