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[en] In clinical proton beam radiation therapy, an RBE of 1.1 relative to megavoltage X-rays is currently being employed at most treatment centers. This RBE pertains to radiation in the spread out Bragg-peak (SOBP) for all tissue systems, all dose levels per fraction and all proton beam energies. As the number of centers and treatment sites for which proton beam therapy continues to increase and additional experimental data is accrued, a re-assessment of the justification for a generic RBE is warranted. In this paper we address: (1) the constancy of the RBE along the central axis from the plateau entrance to the distal SOBP (upstream of the distal edge); (2) RBE as a function of dose (or cell survival level); and (3) the target cell or tissue (α/β) dependency of the RBE. This analysis pertains to modulated proton beams of initial energies of approximately 70-200 MeV and SOBPs of approximately 2-10 cm, respectively. With exceptions, the available experimental data indicate that the RBE of SOBP protons increases with decreasing dose or dose per fraction and increasing depth in the SOBP. with the magnitude of both effects likely being dependent on the α/β ratios of the target cells or tissues. The use of a generic RBE of 1.1 for all tissues, especially those exhibiting low α/β values such as CNS, may be too low. especially at dose levels of ≤ 2 Gy/fraction. Systematic determination of the RBE values dependent upon the three interdependent variables identified in this manuscript (beam depth, dose size and target tissue) will provide an enhanced data base for detailed treatment planning and institutional trial comparisons, thereby maximizing the therapeutic benefit of proton beams. (author)
[en] We present an open-source code library for amorphous track modelling which is suppose to facilitate the application and numerical comparability as well as serve as a frame-work for the implementation of new models. We show an example of using the library indicating the choice of submodels has a significant impact on the modelling outcome.
[en] Dynamic spot scanning with pions of patients with pelvic and abdominal malignancy has demonstrated to date that treatments are well tolerated, that early response rates are favorable, and that morbidity, which is volume and dose related, has been within clinically acceptable limits. The search for optimum treatment factors proceeds
[en] Tritium is a radionuclide that will be used and produced in fusion reactors. Tritium toxicity is well known, but its health consequences are more difficult to assess, due to difficulties in assessing doses and to the very few cases of contamination that have occurred since it started being used. The assessment of risks resulting from tritium exposure is based on ICRP models that enable the calculation of doses in tissues, by means of a weighting factor WR, based on the relative biological effectiveness of the various radioactive emissions. Some authors are currently asking for a revision of the weighting factor used for tritium beta-ray emissions, arguing that tritium could be incorporated into DNA. A review of the extensive research conducted on this subject shows that the relative biological effectiveness of tritium is not so different from that of gamma emissions, which are taken as reference radiations. This supports the drive to keep the current weighting factor of 1 for tritium beta emissions, initially proposed and then reaffirmed by the ICRP.
[en] Seventy patients with T3N0 glottic cancer who received a total dose of 60 Gy in twenty-five 2.4 Gy daily fractions over 5 weeks had an initial post radiation primary recurrence free rate of 65% at 5 years. This provides one more point for the dose response for T3 glottic cancer Radiother Oncol (1999) 15
[en] The RBE theory is based on general microdosimetric concepts and can, therefore, be applied to any kind of ionizing radiation. Application to pions is made feasible by calculating the inherent physical parameters of the theory, which depend on characteristics of radiation energy deposition, for different positions in and components of a pion beam. Emphasis is placed on rationalizing and simplifying the physical fundamentals to start with (radiation field composition, modes and products of interaction) and presenting the final results in a comprehensive and practicable form. (author)