RapidArc exploits customized algorithms to deliver a complete 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 delivering successive arcs. For each arc, the beam aperture (as defined by the multileaf collimator) changes with the gantry angle to match the shape of the tumour.

"At the moment, Varian does Dynamic Arc, which means the clinician can adjust the treatment field every two degrees using the multileaf collimator in the head of the treatment machine," Neil Madle, Varian's director of investor relations, Europe, told medicalphysicsweb recently. "Doing this, you look at the tumour from every angle and you shape the field to the tumour. Now, we have devised a way of combining this with 3D imaging to do VMAT."

In this way, says Varian, it is possible to outstrip more time-consuming IMRT treatment methods, which require machines to make several rotations around the patient or to make repeated stops and starts to set up beam angles. According to the vendor, "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."

The two FDA clearances for RapidArc cover the treatment hardware and the RapidArc treatment planning software module in Varian's Eclipse treatment planning system. Varian will begin taking orders for RapidArc immediately, and will begin delivering to customers in the spring.

• Varian has completed the acquisition of Pan-Pacific Enterprises, the largest independent distributor of medical X-ray tubes in China. Varian is acquiring the privately held business for approximately $2 million in cash plus an additional amount (not disclosed) based on achievement of specified milestones with respect to marketing, sales and distribution of Varian X-ray imaging products in China. Pan-Pacific employs around 30 staff at facilities in Beijing and Shanghai.