During the last week of April, Varian service technicians added the RapidArc technology to the UAB Health System's existing Varian platform for image-guided IMRT. "The installation process went very smoothly," said Richard Popple, assistant professor and RapidArc team leader at UAB. "Our initial pre-clinical testing of RapidArc has verified that sophisticated treatments can be delivered within two minutes with dosimetry that is the same as, or better than, other IMRT techniques."
RapidArc exploits customized algorithms to deliver a complete image-guided IMRT treatment in a single rotation of the linac around the patient, a procedure also known as volumetric modulated arc therapy (VMAT). Modulation is achieved by simultaneously varying the dose delivery rate and the shape of the treatment aperture during the one rotation of the gantry.
According to Varian, "by varying three parameters simultaneously - the speed of rotation, the beam-shaping aperture and the dose delivery rate - doctors can create finely shaped IMRT dose distributions that more closely match the size and shape of the tumour while sparing healthy tissues."
Ivan Brezovich, chief of medical physics at UAB, explained the thinking behind the RapidArc upgrade: "A faster treatment reduces the chance that the patient will move during the treatment and affect the accuracy of the targeting. Even if a patient keeps completely still, involuntary anatomical shifts can occur within the body during a long treatment, which may compromise treatment precision."
He continued: "With a prostate tumour, for example, gradual filling of the bladder can displace the target by a few millimetres. Given the time and effort that goes into getting a patient properly positioned for an accurate treatment, we're excited about a treatment approach that has a better chance of preserving that accuracy."
• Last month, Varian reported that it has received more than 60 orders for RapidArc since the system's commercial launch in January.