The physical basis and future of radiation therapy

Abstract

The remarkable progress in radiation therapy over the last century has been largely due to our ability to more effectively focus and deliver radiation to the tumour target volume. Physics discoveries and technology inventions have been an important driving force behind this progress. However, there is still plenty of room left for future improvements through physics, for example image guidance and four-dimensional motion management and particle therapy, as well as increased efficiency of more compact and cheaper technologies. Bigger challenges lie ahead of physicists in radiation therapy beyond the dose localisation problem, for example in the areas of biological target definition, improved modelling for normal tissues and tumours, advanced multicriteria and robust optimisation, and continuous incorporation of advanced technologies such as molecular imaging. The success of physics in radiation therapy has been based on the continued "fuelling" of the field with new discoveries and inventions from physics research. A key to the success has been the application of the rigorous scientific method. In spite of the importance of physics research for radiation therapy, too few physicists are currently involved in cutting-edge research. The increased emphasis on more "professionalism" in medical physics will tip the situation even more off balance. To prevent this from happening, we argue that medical physics needs more research positions, and more and better academic programmes. Only with more emphasis on medical physics research will the future of radiation therapy and other physics-related medical specialties look as bright as the past, and medical physics will maintain a status as one of the most exciting fields of applied physics.

Figure 1

100 years of development in radiation therapy have made a difference. Comparison of an X-ray treatment plan from the early 1900s ((a), from [8]) and a proton treatment plan from the early 2000s ((b), courtesy of AW Chan and AV Trofimov, MGH Boston).

Figure 2

Spectrum of medical physics roles. Each of the four primary roles: cutting-edge research, translational research, technology improvement and clinical implementation, are equally important, even although they are not, and do not need to be, equally represented.

Figure 3

Optimal medical physics chain. Each of the links should be equally strong for optimal development of the medical physics field. Weakening of any of the links will result in prolonged time from the discovery to clinical implementation, and a break of any of the links would lead to the break and fall of the whole medical physics field. Time scale is approximate and indicates approximate time horizon of each of the component of the medical physics spectrum.

Figure 4

Suboptimal medical physics chain. Currently we are experiencing an increased emphasis on consolidating the clinical part of the medical physics spectrum, leaving the research part behind. This leads to the prolongation of the time between invention and clinical implementation, particularly severe as the relative time scale is not linear.