MV PHOTON FIELDS

The Problems Associated with Relative Dose Measurements in Small MV Photon Fields

The Problems Associated with Relative Dose Measurements in Small MV Photon Fields

A brief overview of external beam radiotherapy techniques that employ small MV photon fields

An EBRT involves directing rays (also known as radiation or radiation), produced by an external source, at the prostate to destroy cancer cells by blocking their ability to multiply. In external radiotherapy, the rays are emitted beam by a machine located close to the patient; they pass through the skin to reach the tumor (Arnon, Meirow, et al, 2001, p. 394-403). The rays are directed onto the tumor and sometimes, on some nodes connected to the affected organ. External radiation therapy is called "percutaneous" as the rays pass through the skin to reach the tumor. These rays are emitted in bundles targeted to the tumor by a machine called a linear particle accelerator. This is a local treatment (or locoregional) of prostate cancer that is to say that acts directly on the affected area. This treatment is performed by a radiation oncologist (Boris, Selby, et al, 2007, p. 36-40).

External radiotherapy is a standard treatment for localized prostate cancer and locally advanced. Link to the: Treatment of prostate cancer according to their stage. Radiation damages the cells mainly in their DNA, that is to say, the identity card of the cells. DNA is found in the nucleus of each cell of the body. When DNA is damaged, cells can no longer multiply and eventually die. This destruction is not immediate, it occurs when cells are induced to divide. In a brachytherapy radiation from radioactive sources are as in external beam radiation, they are produced by machines, most often today linear accelerators of particles (Harrison, Chadha, et al, 2002, p. 492-508). There are several types of rays that penetrate more or less in the body and deposit their energy in different ways. Radiation most commonly used in external radiotherapy is currently the photons or X-rays (used in 90% of cases) very high energy. More rarely, it also uses protons and other particles, carbon ions, are being evaluated (Bogdanich, Walt, et al, 2010, p. 28-35). The rays cause damage to the cells they touch, whether healthy or cancerous. This is why the side effects of radiotherapy (Boris, Selby, et al, 2007, p. 36-40).

The challenge of any radiotherapy treatment is therefore to maximize its effectiveness on the prostate while minimizing toxicity to healthy tissue and surrounding organs, also known as organs at risk: the rectum, the bladder and the anal canal particular. This requires focus as accurately as possible the irradiation of the prostate volume: as such, the technological progress of recent years is considerable (Nieder, Milas, et al, 2000, p. 200-209). We must also determine, for each patient, the optimal dose of radiation that is to say sufficient to destroy the tumor but taking into account the tolerance dose of organs at risk. The radiation dose is expressed in gray, abbreviated ...