Despite the obvious potential, however, delegates were left in little doubt that IGRT is very much a "works in progress". For one thing, IGRT comes at a premium, adding around 30% to the cost of conventional radiotherapy units by some estimates. For another, there are many process-related challenges that will have to be tackled before IGRT technologies become a fixture in the clinical mainstream. Physicists and clinicians still need to get their heads around all manner of residual uncertainties, among them inaccuracies in operator alignment; geometric uncertainties in calibration; imperfections in applying the corrections; intrafraction motion; and systematic errors introduced by initial contouring errors.

None of which is going to be straightforward given that, according to one speaker at IGRT II, training and education in radiation therapy are lagging several years behind IGRT's clinical implementation. Technical and financial challenges notwithstanding, there's the added complication that the supply-side bandwagon is building up a considerable head of steam. Slick product marketing is very much in evidence and a posse of equipment makers are all pushing their own variations on the IGRT theme - each one claiming a better approach than the next one on price, performance or both.

For now, though, and despite what the vendors might claim, IGRT remains a "show me" technology. What's more, there are no short cuts and no half measures when it comes to throwing off that tag. Bhadrasain Vikram, chief of the clinical radiation oncology branch at the US National Cancer Institute, pulled no punches when he noted that the best way to determine if a service like IGRT truly benefits patients is to evaluate that service in a controlled clinical trial. "Participation in clinical trials is a logical measure of commitment to quality improvement...It provides a means to measure, monitor and improve patients' outcomes," he told IGRT II delegates.

Equally important is the need to maintain clinical vigilance when introducing developmental IGRT technologies and applications. Granted, IGRT may have great potential for decreasing toxicity and/or increasing patient survival in the treatment of some cancers. By the same token, Vikram maintains that IGRT should, for the most part, be utilized in the context of clinical research just now, owing to the very demanding quality assurance and the possibility of harm to patients. "[After all], how often has the perception by academic clinicians that an experimental cancer treatment is superior to standard treatment been proved correct?" he asked, before answering his own question: "So infrequently as to make us all humble."

That means there's one more take-home message from IGRT II: hard data from controlled clinical trials is the best way to prove that IGRT technology doesn't just produce lots of pretty pictures but actually improves patient survival as well. It falls to clinicians, physicists and equipment makers to gather the necessary evidence, and to start that process now.