Biological-based planning maximizes critical organ sparing in fast VMAT for SBRT of prostate, lung and liver lesions

ATLANTA /PRNewswire/ -- High-dose Stereotactic Body Radiation Therapy (SBRT) has emerged as a critical treatment option for patients with prostate, lung and liver cancer. The challenge has been delivering SBRT's large doses as quickly as possible, for improved patient comfort and to reduce the chance the patient will move during treatment delivery. While Volumetric Modulated Arc Therapy (VMAT) promises much faster treatment delivery, clinicians have been reluctant to sacrifice plan quality to deliver therapy faster. The Editor Pick in the January 2012 issue of Medical Physics is an article by Quentin Diot, Brian Kavanagh, Robert Timmerman, and Moyed Miften that demonstrates that the use of Monaco biological-based planning meets the need for fast SBRT with high quality plans.

"We found that using biological-based optimization and VMAT we could deliver faster treatments with comparable or better plan quality for patients with prostate, lung and liver patients, compared to fixed gantry [i.e., step-and-shoot] IMRT," says the University of Colorado School of Medicine's Moyed Miften, Ph.D., a senior-author of the paper, Biological-based optimization and volumetric modulated arc therapy delivery for stereotactic body radiation therapy.*
The researchers found that biological-based planning achieves the goal of sparing organs-at-risk (OARs) - the physician's main concern when delivering SBRT's significantly larger radiation doses per treatment fraction. Subjects included 24 SBRT patients with prostate, liver or lung cancer.

Biological-based planning v. physical planning

Elekta's Monaco® uses biological-based plan optimization, in contrast to planning systems that offer only physical planning.

The optimization process entails the twin goals of maximizing the dose to the target and minimizing the dose to OARs. Because targets and OARs are contiguous, these goals compete and the optimizer needs to make the appropriate trade-offs.

With physical-based optimization, the planner manually enters points (volume receiving a given dose or dose volume (DV)) to constrain the optimization based on available clinical data that demonstrate a correlation between tumor control and normal tissue complications and particular DV metrics.

"These metrics are only surrogates of the biological response and different plans that meet the same discrete constraints can have a very different biological outcome," explains Quentin Diot, Ph.D., of the University of Colorado School of Medicine. "Conversely, biological-based optimization - such as that provided by Monaco - uses model functions directly related to biological outcomes to guide the optimization, and can distinguish between apparently equivalent physical plans."

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