Arc radiotherapy treatments: Breakthrough in image-guided targeting of prostate tumours

4 Mar 2010

Researchers in the US and Denmark have made a breakthrough in image-guided targeting of prostate tumours during arc radiotherapy treatments. In research partially supported by Varian Medical Systems (NYSE: VAR), physicists at Stanford University (California, USA) and Aarhus University Hospital (Aarhus, Denmark) have devised a method for 'real-time' tracking of the prostate motion using Varian's On-Board Imager that shows promise in paving the way for advanced clinical treatments.

Arc therapy techniques such as Varian's RapidArc technology are fast and efficient radiotherapy treatments delivered in a continuous rotation of the treatment machine around the patient. The position of the target must be updated in real-time in order for the dynamic multi-leaf collimator (DMLC) to track tumour motion. To date, a combination of MV portal images and kV orthogonal images have been tested to achieve this.

kV image beam is not obscured by the treatment DMLC

"Acquiring mega-voltage images is not ideal during RapidArc because the DMLC can block the view of the target during the treatment," says Per Rugaard Poulsen, lead author of the research. "The kV image beam is not obscured by the treatment DMLC making the markers visible from all treatment angles, unlike with the MV beam."

To test the system, arc radiotherapy was delivered to a 'motion phantom' implanted with fiducial markers while continuously imaging with the kV beam. The target position was determined from these images, acquired from different projections during the arc, enabling the researchers to determine information about its 3D motion. This single imager based DMLC tracking system was shown to have sub-millimetre accuracy for most types of prostate motion. Precise alignment of the treatment beam with the tumour position is vital in radiotherapy treatments, as it can reduce the likelihood of complications due to the treatment.

"The results confirm what has been seen in simulation studies and show that the method is very robust to experimental uncertainties," adds Per Rugaard Poulsen. "We've demonstrated that image-based tracking during arc radiotherapy can be done completely without MV images, which is an important step along the way to image-based tracking during arc treatment delivery."

Corey Zankowski, Varian's senior director of product management, said, "This research paves the way for real-time tracking of the DMLC with tumour motion during advanced arc therapy treatments, which should allow clinicians to reduce treatment margins around the tumour. Varian is committed to working closely with industry experts and researchers to enhance treatment accuracy with the goal of improving treatment outcomes."

Source: Varian Medical Systems, Inc.