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Proton therapy or proton beam therapy is a medical procedure, a type of particle therapy that uses a beam of protons to irradiate diseased tissue, most often in the treatment of cancer. Proton therapy's chief advantage over other types of external beam radiotherapy is that as a charged particle the dose is deposited over a narrow range and there is minimal exit dose. ==Description== (詳細はionizing radiation. In proton therapy, medical personnel use a particle accelerator to target a tumor with a beam of protons.〔O. Jakel: State of the art in hadron therapy. AIP Conference Proceedings, vol. 958, no.1, 2007, pp. 70-77〕〔"Zap! You're not dead." ''Economist'', 8 September 2007. 384 (8545):13-14〕 These charged particles damage the DNA of cells, ultimately killing them or stopping their reproduction. Cancerous cells are particularly vulnerable to attacks on DNA because of their high rate of division and their reduced abilities to repair DNA damage. Due to their relatively large mass, protons have little lateral side scatter in the tissue; the beam does not broaden much, stays focused on the tumor shape and delivers only low-dose side-effects to surrounding tissue. All protons of a given energy have a certain range; very few protons penetrate beyond that distance.〔 Furthermore, the dose delivered to tissue is maximum just over the last few millimeters of the particle’s range; this maximum is called the Bragg peak.〔Camphausen KA, Lawrence RC. ("Principles of Radiation Therapy" ) in Pazdur R, Wagman LD, Camphausen KA, Hoskins WJ (Eds) (Cancer Management: A Multidisciplinary Approach ). 11 ed. 2008.〕 To treat tumors at greater depths, the proton accelerator must produce a beam with higher energy, typically given in eV or electron volts. Proton therapy treats tumors closer to the surface of the body with lower energy protons. Accelerators used for proton therapy typically produce protons with energies in the range of 70 to 250 MeV (mega electron volts; million electron volts). Adjusting proton energy during the treatment maximizes the cell damage the proton beam causes within the tumor. Tissue closer to the surface of the body than the tumor receives reduced radiation, and therefore reduced damage. Tissues deeper in the body receive very few protons, so the dosage becomes immeasurably small. In most treatments, protons of different energies with Bragg peaks at different depths are applied to treat the entire tumor. These Bragg peaks are shown as thin blue lines in the figure to the right. The total radiation dosage of the protons is called the ''spread-out Bragg peak'' (SOBP), shown as a heavy dashed blue line in figure to the right. It is important to understand that, while tissues ''behind'' or ''deeper than'' the tumor receive no radiation from proton therapy, the tissues ''in front of'' or ''shallower than'' the tumor receive radiation dosage based on the SOBP. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「proton therapy」の詳細全文を読む スポンサード リンク
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