Focus on Heavy Ions in Biophysics and Medical Physics

Abstract

Interest in energetic heavy ions is rapidly increasing in the field of biomedicine. Heavy ions are normally excluded from radiation protection, because they are not normally experienced by humans on Earth. However, knowledge of heavy ion biophysics is necessary in two fields: charged particle cancer therapy (hadrontherapy), and radiation protection in space missions.The possibility to cure tumours using accelerated heavy charged particles was first tested in Berkeley in the sixties, but results were not satisfactory. However, about 15 years ago therapy with carbon ions was resumed first in Japan and then in Europe. Heavy ions are preferable to photons for both physical and biological characteristics: the Bragg peak and limited lateral diffusion ensure a conformal dose distribution, while the high relative biological effectiveness and low oxygen enhancement ration in the Bragg peak region make the beam very effective in treating radioresistant and hypoxic tumours. Recent results coming from the National Institute of Radiological Sciences in Chiba (see the paper by Dr Tsujii and co-workers in this issue) and GSI (Germany) provide strong clinical evidence that heavy ions are indeed an extremely effective weapon in the fight against cancer. However, more research is needed in the field, especially on optimization of the treatment planning and risk of late effects in normal tissue, including secondary cancers.On the other hand, high-energy heavy ions are present in galactic cosmic radiation and, although they are rare as compared to protons, they give a major contribution in terms of equivalent dose to the crews of manned space exploratory-class missions. Exploration of the Solar System is now the main goal of the space program, and the risk caused by exposure to galactic cosmic radiation is considered a serious hindrance toward this goal, because of the high uncertainty on late effects of energetic heavy nuclei, and the lack of effective countermeasures. Risks include carcinogenesis, late degenerative tissue effects (including damage to the central nervous system), and hereditary effects. For these studies, microbeams represent an essential tool, considering that in space each cell in the human body will not experience more than one heavy-ion traversal. Both NASA and ESA are investing important resources in ground-based space radiation research programs, to reduce risk uncertainty and to develop countermeasures.For both cancer therapy and space radiation protection a better understanding of the effects of energetic heavy ions is needed. Physics should be improved, especially the measurements of nuclear fragmentation cross-sections, and the transport calculations. Biological effects need to be studied in greater detail, and clearly only understanding the mechanisms of heavy-ion induced biological damage will reduce the uncertainty on late effects in humans.This focus issue of New Journal of Physics aims to provide the state-of-the-art of the biophysics of energetic heavy ions and to highlight the areas where more research is urgently needed for therapy and the space program. Focus on Heavy Ions in Biophysics and Medical Physics ContentsResearch needed for improving heavy-ion therapy G Kraft and S D KraftIonization and excitation cross sections for the interaction of HZE particles in liquid water and application to Monte Carlo simulation of radiation tracks Ianik Plante and Francis A CucinottaDose calculations at high altitudes and in deep space with GEANT4 using BIC and JQMD models for nucleus-nucleus reactions L Sihver, D Matthiä, T Koi and D MancusiHeavy ion microprobes: a unique tool for bystander research and other radiobiological applications K O Voss, C Fournier and G Taucher-ScholzHeavy ions light flashes and brain functions: recent observations at accelerators and in spaceflight L NariciClinical advantages of carbon-ion radiotherapy Hirohiko Tsujii, Tadashi Kamada, Masayuki Baba, Hiroshi Tsuji, Hirotoshi Kato, Shingo Kato, Shigeru Yamada, Shigeo Yasuda, Takeshi Yanagi, Hiroyuki Kato, Ryusuke Hara, Naotaka Yamamoto and Junetsu MizoeHeavy-ion effects: from track structure to DNA and chromosome damage F Ballarini, D Alloni, A Facoetti and A OttolenghiShielding experiments with high-energy heavy ions for spaceflight applications C Zeitlin, S Guetersloh, L Heilbronn, J Miller, N Elkhayari, A Empl, M LeBourgeois, B W Mayes, L Pinsky, M Christl and E KuznetsovHeavy charged particles in radiation biology and biophysics H Nikjoo, S Uehara, D Emfietzoglou and A BrahmeImpact of track structure calculations on biological treatment planning in ion radiotherapy Thilo Elsässer, Richard Cunrath, Michael Krämer and Michael ScholzThe physical basis for the biological action of heavy ions Jürgen KieferSecondary beam fragments produced by 200 MeV u−1 12C ions in water and their dose contributions in carbon ion radiotherapy K Gunzert-Marx, H Iwase, D Schardt and R S Simon