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Different takes on image guidance
16.22 Thursday ET: The battle for America is over - at least for a day or two until the Democrat and Republican fund-raising bandwagons start rolling for the 2008 presidential election. Here in Philadelphia, meanwhile, the battle for scientific kudos and equipment sales at the 48th annual ASTRO meeting is also done and dusted, with the final few conference sessions having concluded this morning and the miniature city that was the trade exhibition now being dismantled and packed away in readiness for shipping. Yet while all the talking and all the networking are done, there’s still unfinished business when it comes to the write-up…
Following on from yesterday’s introductory post on IGRT, today’s report and Friday’s will feature some of the companies who majored on the image guidance theme at the ASTRO trade show. The coverage is by no means comprehensive, but rather intended to be illustrative of the range of alternatives out there in the market. So if you’re one of the vendors that hasn’t made the cut, remember it was just me versus 200+ exhibitors versus the clock. In any case, don’t get mad, get even - and you can do that by adding your own perspective on IGRT via the easy-to-use commenting facility within this blog.
Think robotic, think radiosurgery
First port of call was Accuray, the US company which has pioneered the CyberKnife System for robotic radiosurgery. Among the new products featured on its ASTRO roster was the Xsight Lung Tracking System. One of a suite of products for the treatment of peripheral lung tumours, Xsight Lung works in combination with CyberKnife to track, detect and compensate for the motion of the tumour and patient during the breathing cycle. What’s more, it does so non-invasively without the need for gating or breath-hold techniques.
During lung radiosurgery, “the major challenge is motion compensation”, explained Omar Dawood, Accuray’s senior manager, clinical programmes, in a booth presentation. Xsight Lung initially references on the patient’s bony anatomy to set up the patient globally. It then uses sophisticated image processing and registration techniques to directly lock onto and track the tumour throughout radiosurgery treatment.
The end game here for Accuray is a motion-tracking and compensation scheme that eliminates the need for invasive placement of gold fiducials in the lung tumour - a procedure which has been associated with a high risk of pneumothorax and chest-tube placement.
“This [Xsight Lung] is a big breakthrough, with shorter time to treatment,” added Dawood. “Evaluation of clinical data demonstrates that it works well for peripheral lung tumours greater than 15 mm in size, with a targeting accuracy better than 1.5 mm.”
Accuray’s previous generation of motion-compensating technology is called the Synchrony Respiratory Tracking System. Launched in 2004, Synchrony uses LED markers on the chest and implanted gold fiducials to visualize the tumour internally through treatment. According to Dawood, “Xsight Lung incorporates the benefits of Synchrony without requiring fiducial markers.”
Also debuting at ASTRO were Accuray’s
• Xchange Robotic Collimator Changer, which has the automated ability to change secondary collimators during CyberKnife treatment. This eliminates the need to re-enter the treatment room and helps to minimize related delays.
• 4D Treatment Optimization and Planning System, which takes into account not only the movement of the tumour, but also the movement and deformation of tissue. The aim is to enable clinicians to better deliver the prescribed radiation dose to the targeted area while minimizing damage to surrounding healthy tissue.
True stories
A few booths away and another take on image guidance was being pushed by TomoTherapy (Madison, WI). Here the emphasis was not just on image guidance - and accuracy in daily patient set-up - but also on adaptation (i.e. what the clinician is able to do with the images acquired during the course of treatment).
First some context. TomoTherapy’s flagship product, the Hi.Art conformal radiotherapy system, comprises a linac mounted on a rigid ring gantry (as opposed to a C-arm). The technology was pioneered by company founders Thomas “Rock” Mackie and Paul Reckwerdt at the University of Wisconsin-Madison in the early 1990s. The result of this innovation: 360 degree helical delivery of IMRT with integrated megavoltage (MV) CT imaging (think of it as IG-IMRT).
Unveiled at ASTRO, CTrue is the latest iteration of TomoTherapy’s CT imaging technology for IMRT. In a product presentation on the company’s booth, Liz Frisch, TomoTherapy’s clinical applications manager, called CTrue “the gold standard for IGRT”, allowing “you to image your patients every day if you want” for comparison with the kV CT image obtained at the treatment planning stage. In a related press announcement, Mackie was even more bullish: “If you don’t have CTrue technology, you cannot use images to quantitatively assess the progress of treatment and, when necessary, to provide adaptation during the course of radiotherapy. And adaptive radiotherapy is all about maintaining accuracy and precision throughout the whole course of treatment.”
To sum up: CTrue equates to MV CT imaging for all anatomical locations - and with very low delivered dose - to ensure accurate delivery of helical IMRT. Subsequent quantitative analysis using the company’s Planned Adaptive software provides the logical extension of that capability: “You can also adapt the plan throughout the course of treatment to maintain the doctor’s prescription,” added Frisch.
