Some 13 years ago, the European Organisation for Research and Treatment of Cancer (EORTC) organized a large meeting devoted entirely to neutron therapy, its original promise and, of course, its clinical disappointments. The term ‘‘charged particles’’ has changed the emphasis, with realistic expectations of better clinical outcomes; the best available radiation dose distributions can now be achieved due to the Bragg peak effect that results from the deceleration of charged particles (CP) in tissues; neutrons and X-rays carry no charge and do not exhibit such selectivity in dose deposition. Consequently, the application of curative radiotherapy in the future is expected to rely more and more on these physical advantages [1]. The reader who may be unfamiliar with terms and some of the acronyms used should refer to Tables 1 and 2. This article is written to inform those working in the various disciplines associated with radiotherapy in the UK about the present and intended developments in Europe, Japan and North America and how these are organized and funded. It is not intended to be an account that proves that these new forms of radiation therapy, which are being tested in phase I/II studies in an increasing number of cancer sites, are better than the techniques presently available in the UK; considerable prospective research and development will be necessary to show not only that this is unequivocally so, but also to investigate the actual cost-benefits comparedwith other Xray based techniques such as intensity-modulated radiotherapy (IMRT)/tomotherapy/conformal radiotherapy. Other articles have been written elsewhere regarding this increasingly important topic [2–4]. Under the leadership of Prof. Ugo Amaldi and Prof. Andre Wambersie for Heavy Charged Particles in Biology & Medicine (HCPBM) and European Network for Light Ions (ENLIGHT), respectively, this combined meeting – held over 4 days and attended by about 150 delegates – discussed the merits of various CP ranging from protons to helium and carbon ions in clinical practice. The potential for routine use of CP has increased for a variety of reasons: impressive initial clinical results; improved imaging that allows safe application of the better dose deposition; industrial production of turnkey centres that can be situated in a large hospital, and also increasing critique of the limitations of X-ray based radiotherapy based on threedimensional dose distributions made available by faster computers. Although CP have been used for a many years (50 years at Boston, USA) the treatments were disadvantaged by several factors: relatively poor imaging; location in what were essentially physics laboratories; limited beam energies and beam availability, resulting in treatments of a very small range of cancers. Japan, followed by Germany, has pioneered the use of light ions in modern medicine, after some promising results were initially obtained at Berkeley, USA and PSI in Switzerland (initially with pions – or pi-mesons – using more traditional radiation field arrangements and treatment planning methods). The ions, in contrast to protons, have substantially increased linear energy transfer (LET) properties that cause additional biological effects, which can counteract tumour intrinsic and hypoxic radioresistance; the latter properties were those from which clinical advantages were predicted for neutrons, but neutral particles cannot be deposited with selective advantage as in the case of CP and, largely as a consequence of this, they failed to improve the therapeutic index [5, 6]. The initial claims of the efficacy of neutron therapy at the phase I/II study level – and which were not substantiated in subsequent phase III randomized studies – cannot be compared fairly with the results presently being claimed for CP therapy because tissue side effects were classified in a rudimentary manner during the initial neutron studies, whereas CP studies are presently assessed with the most modern criteria. The British Journal of Radiology, 79 (2006), 278–284
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Aug 31, 2010
Serge N Zagoulaev 
Open Access