Rationale and Potential Clinical Applications for CyberKnife Robotic IMRT™

The CyberKnife® System as an Image-guided Intensity Modulated Radiotherapy Device: Rationale and Potential Clinical Applications for CyberKnife Robotic IMRT™

Donald B. Fuller, M.D., Radiation Oncologist Radiosurgery Medical Group (RSMG); CyberKnife Centers of San Diego

In clinical practice, the CyberKnife® Robotic Radiosurgery System has been almost exclusively used as a radiosurgical device, engineered to deliver conformal, ablative radiation treatments in one to five fractions to a wide variety of malignant lesions in the CNS, head and neck, lung, liver, pancreas, prostate and other sites.1-8 Although there is no medical reason why this device has not been used to deliver conventionally fractionated radiotherapy, this function has not previously been described, presumably due to the long treatment times associated with early-generation CyberKnife Systems. Nevertheless, the MultiPlan® Treatment Planning System is capable of computing very elegant intensity modulated radiotherapy (IMRT) dose distributions, and improvements in device efficiency have made the delivery of these IMRT plans feasible in clinical practice, thus leading to new CyberKnife treatment applications that would best be described as “Robotic IMRT™.”

The new CyberKnife VSI™ platform includes a number of enhancements that improve efficiency, including Sequential Optimization treatment planning, the Iris™ Variable Aperture Collimator (which allows for modulation of the beam during treatment9,15), the increased dose rate of a 1,000 MU/min linear accelerator and a 20% increase in robotic traversal speed. In addition, a treatment time reduction tool accessed during plan optimization allows the user to reduce the total number of treatment beams and nodes while still meeting treatment plan objectives.

Collectively, these enhancements create a device that can reduce treatment times by over half compared with predecessor CyberKnife Systems, while maintaining the precision and accuracy of the CyberKnife product.

SOURCE: ACCURAY FOCUS NEWSLETTER JAN, 2010

LIVER METASTASES TREATMENT

Stereotactic body radiation therapy for liver metastases


O Dawood, A Mahadevan, K Goodman ,European J Cancer 2009;45:2947-2959.





This review focuses on stereotactic body radiation therapy (SBRT) as an alternative, non-invasive approach to the treatment of liver metastases. Treatment considerations of SBRT for liver metastases are presented with particular emphasis on the challenges of organ motion and the low tolerance of the surrounding hepatic parenchyma. Multiple approaches to tumor motion are discussed, including tumor tracking versus motion-compensation techniques. Issues of patient eligibility criteria, patient set-up, target definition, treatment dosimetry and fractionation are also discussed. Clinical results to date from 15 published reports, including a summary of the latest in-press results from Stanford using the CyberKnife System, are presented. These clinical reports demonstrate the safety and efficacy of SBRT for liver metastasis with 18-month and 2-year local control rates ranging from 71-93% and 71-86%, respectively.


The review concludes by stressing the importance of addressing hepatic tumor motion to ensure the dose reaches the tumor and spares the surrounding normal tissue. The authors suggest more rigorous phase II clinical studies are necessary to establish the long-term durability of efficacy and toxicity results.


SOURCE : FOCUS NEWSLETTER - JAN 2010

CYBERKNIFE FOR GASTRIC CANCERS

Stereotactic body radiotherapy for isolated para-aortic lymph node recurrence after curative resection in gastric cancer

Metastases from gastric cancer are common and can progress rapidly; even with aggressive treatment 5-year survival rates are low. However, researchers from Korea Institute of Radiological & Medical Sciences hypothesized that there is a certain population of such patients in whom the disease follows a more indolent course, based on studies of patients with
resected liver metastases. This population may benefit from SRS of isolated metastases from
gastric primaries. Thus, they treated 7 such patients with the CyberKnife® System, delivering 45 to 51 Gy (median 48 Gy) in 3 fractions. The patients were followed for 14 to 33 months (median 26 months). Local control was achieved in 6 of 7 patients; 2 patients were disease-free, 3 were alive with disease, and 2 patients died of disease progression. Three-year actuarial overall survival was 43%, and disease-free survival was 29%. The authors conclude that the results support their hypothesis that an indolent subgroup with less aggressive disease progression who could benefit
from the use of local treatments such as CyberKnife Radiosurgery.
 
Source: Accuray's focus newsletter