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      Basics of particle therapy I: physics

      , MS, , MD

      Radiation Oncology Journal

      The Korean Society for Radiation Oncology

      Proton, Neutron, Carbon ion, Particle therapy

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          Abstract

          With the advance of modern radiation therapy technique, radiation dose conformation and dose distribution have improved dramatically. However, the progress does not completely fulfill the goal of cancer treatment such as improved local control or survival. The discordances with the clinical results are from the biophysical nature of photon, which is the main source of radiation therapy in current field, with the lower linear energy transfer to the target. As part of a natural progression, there recently has been a resurgence of interest in particle therapy, specifically using heavy charged particles, because these kinds of radiations serve theoretical advantages in both biological and physical aspects. The Korean government is to set up a heavy charged particle facility in Korea Institute of Radiological & Medical Sciences. This review introduces some of the elementary physics of the various particles for the sake of Korean radiation oncologists' interest.

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          Most cited references 56

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          Intensity-modulated radiation therapy, protons, and the risk of second cancers.

           Eric Hall (2006)
          Intensity-modulated radiation therapy (IMRT) allows dose to be concentrated in the tumor volume while sparing normal tissues. However, the downside to IMRT is the potential to increase the number of radiation-induced second cancers. The reasons for this potential are more monitor units and, therefore, a larger total-body dose because of leakage radiation and, because IMRT involves more fields, a bigger volume of normal tissue is exposed to lower radiation doses. Intensity-modulated radiation therapy may double the incidence of solid cancers in long-term survivors. This outcome may be acceptable in older patients if balanced by an improvement in local tumor control and reduced acute toxicity. On the other hand, the incidence of second cancers is much higher in children, so that doubling it may not be acceptable. IMRT represents a special case for children for three reasons. First, children are more sensitive to radiation-induced cancer than are adults. Second, radiation scattered from the treatment volume is more important in the small body of the child. Third, the question of genetic susceptibility arises because many childhood cancers involve a germline mutation. The levels of leakage radiation in current Linacs are not inevitable. Leakage can be reduced but at substantial cost. An alternative strategy is to replace X-rays with protons. However, this change is only an advantage if the proton machine employs a pencil scanning beam. Many proton facilities use passive modulation to produce a field of sufficient size, but the use of a scattering foil produces neutrons, which results in an effective dose to the patient higher than that characteristic of IMRT. The benefit of protons is only achieved if a scanning beam is used in which the doses are 10 times lower than with IMRT.
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            Initial events in the cellular effects of ionizing radiations: clustered damage in DNA.

            General correlations are found between the detailed spatial and temporal nature of the initial physical features of radiation insult and the likelihood of final biological consequences. These persist despite the chain of physical, chemical and biological processes that eliminate the vast majority of the early damage. Details of the initial conditions should provide guidance to critical features of the most relevant early biological damage and subsequent repair. Ionizing radiations produce many hundreds of different simple chemical products in DNA and also multitudes of possible clustered combinations. The simple products, including single-strand breaks, tend to correlate poorly with biological effectiveness. Even for initial double-strand breaks, as a broad class, there is apparently little or no increase in yield with increasing ionization density, in contrast with the large rise in relative biological effectiveness for cellular effects. Track structure analysis has revealed that clustered DNA damage of severity greater than simple double-strand breaks is likely to occur at biologically relevant frequencies with all ionizing radiations. Studies are in progress to describe in more detail the chemical nature of these clustered lesions and to consider the implications for cellular repair. It has been hypothesized that there is reduced repair of the more severe examples and that the spectrum of lesions that dominate the final cellular consequences is heavily skewed towards the more severe, clustered components.
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              The physics of radiation therapy

               FM Khan,  F.M. Khan,  F Khan (2003)
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                Author and article information

                Journal
                Radiation Oncol J
                Radiation Oncol J
                ROJ
                Radiation Oncology Journal
                The Korean Society for Radiation Oncology
                2234-1900
                2234-3164
                September 2011
                30 September 2011
                : 29
                : 3
                : 135-146
                Affiliations
                Department of Radiation Oncology, Kyung Hee University School of Medicine, Seoul, Korea.
                Author notes
                Correspondence: Jin Oh Kang, MD, Department of Radiation Oncology, Kyung Hee University School of Medicine, 45 Kyungheedae-gil, Dongdaemoon-gu, Seoul 130-701, Korea. Tel: +82-2-958-8664, Fax: +82-2-962-3002, kangjino@ 123456paran.com
                Article
                10.3857/roj.2011.29.3.135
                3429896
                22984664
                Copyright © 2011. The Korean Society for Therapeutic Radiology and Oncology

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Categories
                Review Article

                Oncology & Radiotherapy

                particle therapy, neutron, proton, carbon ion

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