Pioneering Radiotherapy Technology Treats Multiple Brain Metastases

An innovative radiosurgery system targets treatment beams at tumors while rotating continuously around the patient, makes it possible to complete stereotactic radiosurgery sessions many times faster than conventional techniques that use stationary beams.

The Varian RapidArc stereotactic radiosurgery system is a volumetric arc therapy device that delivers a precisely sculpted three-dimensional (3D) dose distribution with a single 360^o rotation of the linear accelerator gantry. It is made possible by a treatment planning algorithm that simultaneously changes three parameters during treatment; leaf interdigitation using a multileaf collimator (MLC), a dynamic "sliding window” approach to beam-shaping, and a patented "gridded gun” to vary the dose rate as a function of the gantry angle.

As a result, a single arc can deliver essentially similar dose distributions compared with intensity-modulated radiation therapy (IMRT) treatment plans that incorporate as many as 36 fields while delivering therapeutic radiation doses to the whole volume of the tumor, rather than slice by slice. Additionally, the treatment-planning algorithm ensures enhanced precision, helping to spare normal healthy tissue. The Varian RapidArc stereotactic radiosurgery system is a product of Varian Medical Systems (Palo Alto, CA, USA).

Researchers from Vrije Universiteit (VU) Medical Center (VUMC; Amsterdam, The Netherlands) began clinical treatments using volumetric modulated arc therapy with the RapidArc in early May 2008 and more than 20 patients have so far been treated. RapidArc was first used to replace IMRT treatments for head and neck, brain, and prostate tumors but from September 2008 onwards RapidArc will replace all conventional treatments at VUMC, since treatments were found to be two to eight times faster than IMRT. VUMC studies with the system were presented at the American Association of Physics in Medicine (AAPM) meeting, held in Houston (TX, USA) in July 2008.

"Our experiences to date have demonstrated that RapidArc appears to be excellent for stereotactic radiosurgery,” said Frank Lagerwaard, M.D., of the department of radiation oncology. "The total time needed for patients to enter and leave the treatment room has decreased to less than 15 minutes as we gain experience. During these treatments the delivery time was just 210 seconds per session.”

By comparison, conventional IMRT stereotactic treatment of three brain metastases using multiple dynamic conformal arcs takes more than 50 minutes from first beam on to last beam off.

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