Institutional experience on the treatment of lung and liver lesions with stereotactic body radiotherapy and Novalis Exactrac Adaptive Gating technique.

Introduction: Gating technique can improve the accuracy of the treatment of lung and liver lesions with SBRT, by monitoring organ tumor motion and irradiating within a selected area of the respiratory cycle.

Methods: We have treated 75 patients (34 lung and 41 liver) with Novalis LINAC SBRT Adaptive Gating Technique. A total of 130 lesions, 49 lung lesions (11 primary NSCLC and 38 metastases) and 81 liver lesions (10 primary and 71 metastases). Prior to treatment, a fiducial marker is implanted and CT simulation is performed in breatholding with infrared external skin markers. Based on these external markers, internal tumor motion is correlated with the external respiratory signal. The outlined PTV includes (CTV=GTV) + 5 mm margin. The following doses are prescribed: liver (5Gy x 10 or 12-20Gy x 3), peripheral lung lesions (15-20 Gy x 3), and central lung lesions (5Gy x 10 or 10 Gy x5). The dose was delivered with multiple coplanar static beams. During patient setup, infrared markers track the respiratory cycle. Exactrac X-Rays localize the internal marker, quantify the tumor movement, and define the "beam on area" by correlating the external marker motion to the internal marker position. Intrafraction verification of the validity of this model is performed in real time by ExacTrac X-Rays.

Results: 130 lesions were evaluated with 90.5% local control at two years [93.8% in lung and 87.3% in liver lesions]. Clinical tolerance was excellent and no lung or liver toxicity grade 3 was observed.

Conclusion: Our clinical experience with Novalis SBRT Adaptive Gating shows that this technique is safe and efficient for the treatment of lung and liver lesions, while reducing the volume of irradiated healthy tissue. Intrafraction verification improves the treatment accuracy by a real time verification of tumor position.