Proton therapy

In the field of medical procedures, proton therapy, or proton radiotherapy, is a type of particle therapy that uses a beam of protons to irradiate diseased tissue, most often in the treatment of cancer. The chief advantage of proton therapy over other types of external beam radiotherapy is that as a charged particle the dose is deposited over a narrow range of depth, and there is minimal entry, exit, or scattered radiation dose.We cannot say with any conviction that proton beam therapy is “better” overall than radiotherapy. (...) Some overseas clinics providing proton beam therapy heavily market their services to parents who are understandably desperate to get treatment for their children. Proton beam therapy can be very costly and it is not clear whether all children treated privately abroad are treated appropriately. In the field of medical procedures, proton therapy, or proton radiotherapy, is a type of particle therapy that uses a beam of protons to irradiate diseased tissue, most often in the treatment of cancer. The chief advantage of proton therapy over other types of external beam radiotherapy is that as a charged particle the dose is deposited over a narrow range of depth, and there is minimal entry, exit, or scattered radiation dose. Proton therapy is a type of external beam radiotherapy that uses ionizing radiation. In proton therapy, medical personnel use a particle accelerator to target a tumor with a beam of protons. These charged particles damage the DNA of cells, ultimately killing them by 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. Some cancers with specific defects in DNA repair may be more sensitive to proton radiation. Because of 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 penetration range; very few protons penetrate beyond that distance. Furthermore, the dose delivered to tissue is maximized only over the last few millimeters of the particle’s range; this maximum is called the Bragg peak, often referred to as the SOBP. To treat tumors at greater depths, the proton accelerator must produce a beam with higher energy, typically given in eV (electron volts). Accelerators used for proton therapy typically produce protons with energies in the range of 70 to 250 MeV. 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 almost no radiation from proton therapy, the tissues in front of (shallower than) the tumor receive radiation dosage based on the SOBP. Most installed proton therapy systems utilise isochronous cyclotrons. Cyclotrons are considered simple to operate, reliable and can be made compact, especially with the use of superconducting magnets. Synchrotrons can also be used, with the advantage of easier production at varying energies. Linear accelerators, as used for photon radiation therapy, are becoming commercially available as limitations of size and cost are resolved. The first suggestion that energetic protons could be an effective treatment method was made by Robert R. Wilson in a paper published in 1946 while he was involved in the design of the Harvard Cyclotron Laboratory (HCL). The first treatments were performed with particle accelerators built for physics research, notably Berkeley Radiation Laboratory in 1954 and at Uppsala in Sweden in 1957. In 1961, a collaboration began between HCL and the Massachusetts General Hospital (MGH) to pursue proton therapy. Over the next 41 years, this program refined and expanded these techniques while treating 9,116 patients before the cyclotron was shut down in 2002. The world's first hospital-based proton therapy center was a low energy cyclotron centre for ocular tumours at the Clatterbridge Centre for Oncology in the UK, opened in 1989, followed in 1990 at the Loma Linda University Medical Center (LLUMC) in Loma Linda, California. Later, The Northeast Proton Therapy Center at Massachusetts General Hospital was brought online, and the HCL treatment program was transferred to it during 2001 and 2002. By 2010 these facilities were joined by an additional seven regional hospital-based proton therapy centers in the United States alone, and many more worldwide.