Treating patients with real-time tumor tracking using the Vero gimbaled linac system: implementation and first review.

Purpose: To report on the first clinical application of a real-time tumor tracking (RTTT) solution based on the Vero SBRT gimbaled linac system for treatment of moving tumors.

Methods And Materials: A first group of 10 SBRT patients diagnosed with NSCLC or oligometastatic disease in lung or liver was treated with the RTTT technique. The PTV volumes and OAR exposure were benchmarked against the widely used ITV approach. Based on data acquired during execution of RTTT treatments, a first review was performed of the process.

Results: The 35% PTV volume reduction with RTTT of the studied single lesions SBRT irradiations of small target volumes is expected to result in a small (<1%) reduction of lung or liver NTCP. A GTV-PTV margin of 5.0mm was applied for treatment planning of RTTT. From patient data on residual geometric uncertainties, a CTV-PTV margin of 3.2mm was calculated. Reduction of the GTV-PTV margin below 5.0mm without better understanding of biological definition of tumor boundaries was discouraged. Total treatment times were reduced to 34.4 min on average.

Conclusion: A considerable PTV volume reduction was achieved applying RTTT and time efficiency for respiratory correlated SBRT was reestablished with Vero RTTT.