Particle therapy.

Particle therapy is one of the cutting-edge areas of external beam radiotherapy worldwide, and was therefore chosen as the topic for my 2009 British Institute of Radiology President’s conference. Since this meeting, the field has moved on and I am very pleased to now be able to introduce this special issue of the British Journal of Radiology (BJR) on the same subject. Some of the papers in this special issue grew from presentations at the 2009 meeting and others introduce new thoughts, theories and analysis on the subject. Particle therapy represents a coming together of physics research applied to oncology. In some cases it offers the potential for a cure with reduced shortand longterm complications, and in others it offers the possibility for a very substantial dose escalation. Radiotherapy as practised in the UK has improved greatly over the last 8–10 years with the government-led investment programme and massive efforts from all quarters of the community. Although there is more to do, the foundations of high-quality imaging for diagnosis and treatment planning are well-established, making this the right time to make the step to particle therapy. The National Health Service’s (NHS’s) move to proton therapy, through organised patient referral abroad and planning for UK centres, is a welcome start. At the time of writing the NHS continues to deliberate on the number and location of proton therapy facilities, while it is appropriate for a research journal to also focus on the future, especially the contribution that advanced imaging and carbon ions can play in future cancer treatments. There is a strong UK contribution to this special issue in terms of mathematical modelling both retrospectively, to gain maximum benefit from historical experience, and prospectively, to ensure that we embark on particle therapy with the tools at our disposal to predict all important aspects of the delivered dose distributions. Owing to my background, I am particularly pleased to be able to introduce the article from the team at Tsukuba, which includes a discussion of boron neutron capture therapy (BNCT) in the context of dose escalation for invasive brain tumours. This special issue begins with a review of the technology of the field from the Oxford team, Peach et al [1]. This is a rare article in that it is suitable for the nonspecialist reader but includes all the important aspects of the current technology (cyclotrons and synchrotrons) and compares their capabilities with clinical needs. Potential future acceleration technologies are also introduced. As the world embarks on clinical research with protons and carbon ions, it is important that we learn as much as possible for the existing clinical data with high linear energy transfer (LET) particles. The article from Jones et al [2] is an excellent example of the role of mathematical modelling in fully understanding previous experimental data sets, working through in detail some of the observations made during the Hammersmith and Clatterbridge neutron therapy programmes. The relative biological effectiveness (RBE) values of neutron therapy beams are similar to those of carbon ion beams, and all the issues of variability in response associated with tissue type and fraction size are common, so much can be learned from this kind of analysis. This is followed by a wide-ranging and highly detailed review of the role of positron emission tomography (PET) imaging in radiotherapy (Price and Green [3]), with special emphasis on issues associated with high precision radiotherapy delivered by any technology. The role of PET for target volume definition is explored by tumour site in a readable and useful way. The main clinical papers in this special issue concern therapies involving particles with high-LET, carbon ions and BNCT. Jensen et al [4] provide an authoritative review of the current clinical experience with proton and ion beam therapy by focusing on the developments in Heidelberg. The vision of the Heidelberg ion therapy centre is to place the very best radiotherapy within the context of a national specialist centre for cancer research (DKFZ) and this has much to be admired. The article itself reviews different cancer types and outlines the current world experience with X-rays, protons and ions, as appropriate. For each site considered, a summary Address correspondence to: Professor Stuart Green, Hall Edwards Radiotherapy Research Group, University Hospital Birmingham, NHS Foundation Trust, Edgbaston, Birmingham B15 2TH, UK. E-mail: stuart.Green@uhb.nhs. uk The British Journal of Radiology, 84 (2011), S1–S3