Is tomotherapy the future of IMRT?

Intensity-modulated radiotherapy (IMRT) has become established in many clinics round the world and is, arguably, technically feasible in any facility. Serial tomotherapy contributed an extensive role in its introduction into the mainstream in the second half of the 1990s. In tomotherapy, literally "slice therapy", highly conformal treatments are possible because of the advantages available within the treatment planning of the IMRT process. Currently the majority of clinics implementing IMRT are doing so using conventional clinical linear accelerators (Linacs) fitted with an integrated multileaf collimator (MLC). At this point in time we may wonder if there is any scope for further dramatic changes in this new technology. As we venture from IMRT initial implementation into image guided therapy it is clear that major changes in approach are still valid and needed. If, at each treatment fraction, we can ensure that treatments are delivered accurately by integration of volumetric imaging into on-line validation, then we can attempt higher levels of conformality. A new treatment machine, the helical tomotherapy system, is available that combines the benefits of tomotherapy with on-line volumetric imaging. In this article we will review this approach and explore its features.