06.57 Wednesday CT: It's not often that a clinical technology decision is made on the basis of who can make the most noise. Well, perhaps sometimes it is - but certainly never when that noise is being made by plastic clapping hands wielded by an audience of slightly overexcited medical physicists (see picture).
The clinical decision in question was which of the numerous technologies employed for image-guided radiation therapy (IGRT) is most likely to succeed. In a session entitled "The Great Debate: The Future of IGRT Is...", five distinguished speakers presented opening arguments for megavoltage (MV) and kilovoltage (kV) CT, ultrasound-based hybrids, MRI guidance and 3D deformable image registration. As for the audience: well we got to decide the winner via a show of (clapping plastic) hands.
In what was possibly the most entertaining - and certainly the most raucous - scientific conference session that I've ever attended, Marc Kessler (a professor of radiation oncology at University of Michigan Medical School, Ann Arbor, MI) demonstrated a novel, if somewhat unnerving, method of timekeeping. Any speaker running over their allocated time slot found themselves the target of Kessler's Nerf gun (which fires Styrofoam "bullets"). Kessler certainly seemed to be enjoying himself anyway.
Round one of the debate gave each speaker just six minutes to introduce their case. First up was Jean Pouliot of the University of California, San Francisco (San Francisco, CA) who described the advantages of cone-beam and fan-beam MV CT. "It's a long-term dream to turn the imaging machine into the treatment machine," he said. "[With MV CT], the treatment beam is the imaging beam - you treat what you see."
Pouliot rebuffed the claims from other panel members that the technique delivers too high a dose and doesn't give good enough image quality, pointing out that image quality has rapidly increased over the last five years, and continues to do so. "It provides equivalent alignment precision to kV cone-beam CT," he claimed, adding that the dose can be comparable too.
The second speaker to take the stand (and brave the Nerf gun) was Jan-Jakob Sonke of the Netherlands Cancer Institute in Amsterdam. Sonke presented the case for kV cone-beam CT and discussed the latest technology advances, such as 4D guidance to account for respiratory motion. Sonke told the audience how - following a quick vendor survey at the trade show - he concluded that kV CT represents the lowest cost option of all the proposed methods in the debate.
Next up, Wolfgang Tomé of the University of Wisconsin-Madison (Madison, WI) touted the idea of using optically guided 3D ultrasound for IGRT. He noted that ultrasound imaging can be used in combination with intermittent (say, weekly) cone-beam CT scans to minimize any uncertainties in the ultrasound-based alignment, while enabling accurate daily guidance with a large reduction in cumulative dose.
In a slight twist, Tomé actually suggested that none of the technologies in the debate are actually the future of IGRT. What's really needed, he explained, is a means by which to assess metabolic changes during the therapy itself - a scheme he dubbed image-guided treatment. "I can't say that ultrasound is the future of IGRT on its own, but it will play a key role, in conjunction with kV or MV CT," he concluded.
Jan Lagendijk, from the University Medical Center Utrecht in the Netherlands, proposed a novel scheme in which the treatment machine is fully integrated with an MR scanner, enabling precise soft-tissue visualization for treatment guidance and verification.
A key benefit of this technique is its ability to reduce the required margins and minimize normal tissue complications. "You need imaging during the treatment itself, and the only way to do this is with MRI," he declared somewhat controversially. Lagendijk brushed off the criticism from his fellow panellists that such a system doesn't actually exist yet, stating that it will be developed "quicker than expected".
Finally, Kristy Brock of the Princess Margaret Hospital in Canada (Toronto, ON) argued that the future of IGRT lies not in any one imaging modality, but in the use of deformable modelling to combine diagnostic-quality images with daily image guidance. "All these are great imaging technologies but we need to integrate them together," she explained.
And the winner? It was a resounding victory for Brock, proving perhaps that the debate is actually still to be resolved - or maybe never will be. It's likely that all of the above technologies will continue to be employed, and will be further developed and enhanced. As Brock said: "The future of IGRT lies not one of these modalities, but in all of them."