Variable Proton Relative Biological Effectiveness: How Do We Move Forward?

  • Tracy Underwood
    Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts

    Department of Medical Physics and Bioengineering, University College London, London, United Kingdom
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  • Harald Paganetti
    Reprint requests to: Harald Paganetti, PhD, Department of Radiation Oncology, Massachusetts General Hospital, 55 Fruit St, Boston, MA 02114. Tel: (617) 726 5847
    Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
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      In photon radiation therapy, dose prescriptions have been refined over decades of clinical practice to obtain a balance between tumor control and normal tissue damage. Drawing upon this experience, these prescriptions are used as the basis for proton therapy. Historically they have been reduced by a factor of 1.1: a fixed relative biological effectiveness (RBE). Relative biological effectiveness is defined as the ratio of doses required by two radiations to cause the same level of biological effect. The notion that a single scaling factor may be used to equate the effects of two radiations across all biological endpoints and doses is clearly naïve, yet thus far clinical proton therapy has adopted this simplistic approach.
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