www.bewet.fora.pl

yaa6a3e9

Radiotherapy works by targeting high-energy gamma ray or electron beam onto cancer cells, which are more prone to radiation damage than the normal tissues. Linear accelerators are usually multi-modality ionizing radiation generators with associated imaging devices, currently used for delivery of external beam radiotherapy.
Other additional features may be incorporated into the linear accelerators, such as: arc-based IMRT Delivery,[link widoczny dla zalogowanych], total body irradiation,[link widoczny dla zalogowanych], high-dose rate electrons, etc.
Modern linear accelerators are designed to enable intensity- modulated radiotherapy (IMRT). This is a dynamic radiotherapy delivery method which enables good control over the three-dimensional dose distribution: the delivered beam instead of being flat, changes the intensity at different points within the beam.
The technology used in conventional linear accelerators is essentially the same for all linear accelerators. The high energy generation can be achieved either by implementing the “traveling waveguide technology” or by implementing the “standing waveguide technology”. The first approach is simpler and very reliable, while the second approach features a more stable treatment beam. The generated radiation beam is flattened and shaped using collimation devices to form a beam matching the shape of the tumor. The wave guide, the filters and the collimator are mounted on a gantry which rotates around the patient,[link widoczny dla zalogowanych], allowing the tumor to be irradiated from multiple directions. There is a linear accelerators patient coach especially designed to allow irradiation of the patient from multiple directions.
* Step and shoot method: this method consists of delivering a series of different shape fields formed by the MLC to build up a variable intensity pattern. The irradiation is stopped between each field.
Despite the high capital cost of purchasing linear accelerators, their high patient throughput over a long lifespan makes them extremely cost-effective compared with the other treatment options.
* Arc therapy methods: in which the radiation runs continuously and the gantry collimators and MLC leaves are all moving continuously. The dose rate also varies during the delivery. Treatments are delivered in an arc (or sometimes in two arcs). This is probably the best choice for IMRT.
* Dynamic MLC methods: in which the radiation runs constant, while the MLC leaves move across the field at variable speeds.
There are different types of linear accelerator IMRT delivery methods:
The imager systems differ in the degree of complexity of software provided, as well as the ease of use.
Technical Considerations
The linear accelerators’ three-dimensional imaging systems can be materialized in three different ways:
1. Applying diagnostic x-ray cone beam, in plain or orthogonal to the linear accelerators
The following systems are incorporated into the linear accelerators: multileaf collimator (MLC) for beam shaping, capability to deliver intensity modulated radiotherapy (IMRT) and a 3D image guidance system (IGRT). The linear accelerator also provides an electronic portal imaging system for imaging treatment beams.
The operation of linear accelerators should be according to the existing standards and regulations which include: IEC standards, radiation regulations, guidelines for radio therapy room design, etc.
The multileaf collimator is a delicate computer-controlled mechanism. The performance of the collimator depends on its resolution, the leakage radiation and the system penumbra.
The electronic portal imaging device allows verification of patient position on orthogonal two-dimensional images produced by the high-energy treatment beam. The detector used for the portal imaging consists of an amorphous silicon indirect detection flat panel imager.
The contemporary linear accelerators provide either 6 MeV photons in the “low energy” range machines,[link widoczny dla zalogowanych], or dual/triple photon energy and several electron energies.
相关的主题文章：

[link widoczny dla zalogowanych]

Supra TK Society Shoes Attain memorable Birmingham

Supra Cuban Shoes useful learnings concerning dete