Monday, March 21, 2011

Lung Optimized Treatment with the CyberKnife® Robotic Radiosurgery System

Lung Optimized Treatment with the CyberKnife® Robotic Radiosurgery System
Worldwide, lung cancer is the most common cancer in terms of both incidence and mortality, with 1.61 million new cases and 1.38million deaths in 2008.1 An ever growing number of patients with early stage disease are categorized as poor surgical candidatesdue to co-morbidities such as advanced lung and heart disease. For decades these patients were left with few treatment options and were most often treated with external beam radiation therapy (EBRT). EBRT has limited efficacy due to the inclusion of large volumes of normal tissue within the treatment field, limiting the ability to deliver the high doses needed for tumor control.2 Stereotactic body radiation therapy (SBRT) for the lung directly addresses the dose limitations of EBRT. SBRT allows clinicians to deliver much higher
biologically equivalent doses in one to five fractions. Clinical evidence and publications over the last several years have demonstratedsuperior local control results for SBRT as compared to EBRT3-5, and SBRT has become a standard for the treatment of medically inoperable early stage lung cancer.6

Delivering high doses of radiation in five or fewer fractions to lung tumors demands a high degree of precision and accuracy. The Synchrony® Respiratory Tracking Systemis the only available system that provides real-time tracking for tumors that move with respiration.7 Accurate alignment of each treatment beam with the moving target is
maintained by moving the beam dynamically during treatment.

One challenge to offering CyberKnife® SBRT treatments to lung cancer patients has been the system’s reliance on implanted fiducial markers for tracking.8 Developmentsover the past several years, specifically the advent of the Xsight® Lung Tracking System technology9, allow clinicians to offer fiducial-less treatments to a subset of these
patients (typically peripherally located tumors with a minimum dimension of 15 mm). Using the Synchrony System, with or without fiducial markers, CyberKnife SBRT lung cases have been treated with a total GTV-to-CTV expansion of 3 mm and a CTV-to-PTV expansion of 2 mm.10-12

Now, with the introduction of Lung Optimized Treatment, clinicians can offer the option of fiducial-less treatments to all CyberKnife lung patients, regardless of the location
of the tumor. Lung Optimized Treatment includes the current Xsight Lung Tracking System and provides two new tracking modes: 1-View Tracking and 0-View Tracking.

1-View Tracking is designed for cases in which the treatment target is clearly visible and therefore can be tracked in only one of two the X-ray projections. With 1-View Tracking, motion in the non-tracked plane is accounted for using an Internal Target Volume (ITV) expansion in one direction (along the source-detector imager axis of the
visible view). The ITV expansion needed for 1-View Tracking is expected to be slightly larger than the CTV-to-PTV expansion used with the Xsight Lung Tracking System.
0-View Tracking is designed for cases in which the treatment target is not clearly visible in either of the two X-ray projections. In this case, ITV expansion is used in all directions.

The CyberKnife System tracking technology for treatment of lung tumors includes:
1. The Synchrony Respiratory Tracking System, which provides real-time tracking for tumors that move with respiration
2. The Xsight Lung Tracking System and the Fiducial Tracking System, which allow the target to be treated with no ITV expansion
3. The new 1-View Tracking mode, which requires ITV expansion only along the axis normal to the tracking plane
4. The new 0-View Tracking mode, which requires ITV expansion in all directions


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