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Background The CyberKnife Xsight lung-tracking system (XLTS) provides an alternative to fiducial-based target-tracking systems (FTTS) for non-small-cell lung cancer (NSCLC) patients without invasive fiducial insertion procedures. This study provides a method for 3D independent dosimetric verification of the accuracy of the FTTS compared to the XLTS without relying on log-files generated by the CyberKnife system. Methods A respiratory motion trace was taken from a 4D-CT of a real lung cancer patient and applied to a modified QUASAR™ respiratory motion phantom. A novel approach to 3D dosimetry was developed using Gafchromic EBT3 film, allowing the 3D dose distribution delivered to the moving phantom to be reconstructed. Treatments were planned using the recommended margins for one and three fiducial markers and XLTS 2-view, 1-view and 0-view target-tracking modalities. The dose delivery accuracy was analysed by comparing the reconstructed dose distributions to the planned dose distributions using gamma index analysis. Results For the 3%/2 mm gamma criterion, gamma passing rates up to 99.37% were observed for the static deliveries. The 3-fiducial and 1-fiducial-based deliveries exhibited passing rates of 93.74% and 97.82%, respectively, in the absence of target rotation. When target rotation was considered, the passing rate for 1-fiducial tracking degraded to 91.24%. The passing rates observed for XLTS 2-view, 1-view and 0-view target-tracking were 92.78%, 96.22% and 76.08%, respectively. Conclusions Except for the XLTS 0-view, the dosimetric accuracy of the XLTS was comparable to the FTTS under equivalent treatment conditions. This study gives us further confidence in the CyberKnife XLTS and FTTS systems.

Purpose The Xsight lung tracking system (XLTS) utilizes an advanced image processing algorithm to precisely identify the position of a tumor and determine its location in orthogonal x‐ray images, instead of finding fiducials, thereby minimizing the risk of fiducial insertion‐related side effects. To assess and gauge the effectiveness of CyberKnife Synchrony in treating liver tumors located in close proximity to or within the diaphragm, we employed the Xsight diaphragm tracking system (XDTS), which was based on the XLTS. Methods We looked back at the treatment logs of 11 patients (8/11 [XDTS], 3/11 [Fiducial‐based Target Tracking System‐FTTS]) who had liver tumors in close proximity to or within the diaphragm. And the results are compared with the patients who undergo the treatment of FTTS. The breathing data information was calculated as a rolling average to reduce the effect of irregular breathing. We tested the tracking accuracy with a dynamic phantom (18023‐A) on the basis of patient‐specific respiratory curve. Results The average values for the XDTS and FTTS correlation errors were 1.38 ± 0.65  versus 1.50 ± 0.26 mm (superior‐inferior), 1.28 ± 0.48  versus 0.40 ± 0.09 mm (left‐right), and 0.96 ± 0.32  versus 0.47 ± 0.10 mm(anterior‐posterior), respectively. The prediction errors for two methods of 0.65 ± 0.16  versus 5.48 ± 3.33 mm in the S‐I direction, 0.34 ± 0.10  versus 1.41 ± 0.76 mm in the A‐P direction, and 0.22 ± 0.072  versus 1.22 ± 0.48 mm in the L‐R direction. The coverage rate of FTTS slightly less than that of XDTS, such as 96.53 ± 8.19% (FTTS) versus 98.03 ± 1.54 (XDTS). The prediction error, the motion amplitude, and the variation of the respiratory center phase were strongly related to each other. Especially, the higher the amplitude and the variation, the higher the prediction error. Conclusion The diaphragm has the potential to serve as an alternative to gold fiducial markers for detecting liver tumors in close proximity or within it. We also found that we needed to reduce the motion amplitude and train the respiration of the patients during liver radiotherapy, as well as control and evaluate their breathing.

Purpose Stereotactic body radiation therapy (SBRT) for early-stage lung cancer can be achieved with several methods: respiratory gating, body frame, or real-time target and motion tracking. Two target tracking methods are currently available with the CyberKnife® System: the first one, fiducial tracking, requires the use of radio-opaque markers implanted near or inside the tumor, while the other, Xsight® Lung Tracking System, (XLTS) is fiducial-free. With XLTS, targeting is synchronized directly with target motion, which occurs due to respiration. While the former method (fiducial tracking) is well documented, the clinical relevance of the latter (tracking without fiducials) has never been well described to this date. Patients and Methods A study was performed at our department for each patient treated for lung cancer with CyberKnife using XLTS. Selection criteria were: primary or recurring T1 or T2 stage non-small-cell lung cancer (NSCLC) with 15–60 mm tumor size. Initial staging included CT-Scan and FDG-PET. Results Fifty-one patients not amenable to surgery were treated with XLTS. Median follow-up was 15 months (range, 5–30 months). Median tumor size was 24 mm (range, 15–60 mm). Median total dose was 60 Gy (36–60 Gy) in three fractions. Actuarial overall survival was 85.5% (95% CI = 74.5–96%) at 1 year and 79.4% (95% CI = 64–94.8%) at 2 years. Actuarial local control rate was 92% (95% CI = 84–99%) at one1 year and 86% (95% CI = 75–97%) at 2 years. Conclusion Local control and overall survival rates were similar to previous reports that used fiducials for tumor tracking. Toxicity was lower than most studies since tumor tracking did not require fiducial implantion. This fiducial-free method for respiratory motion tracking is a valid option for the most fragile patients.

Background The aim of this study was to explore the influence of image‐guided tumor localization modality (Synchrony tracking vs. Xsight spine‐based localization) on the local efficacy of CyberKnife treatment in lung cancer and lung metastases. Methods Retrospective analysis of 64 patients with pulmonary metastases and primary tumor cases (72 targets) treated with stereotactic body radiotherapy using CyberKnife was conducted. Synchrony respiratory tracking was used to treat 45 targets, and the remaining 27 targets were treated using Xsight spine (with an extended margin to account for positional uncertainty). The median (80%) isodose line (70–94%) covered the planning target volume at a total dose of 6000 cGy delivered in three fractions. Local efficacy was evaluated by Response Evaluation Criteria in Solid Tumors, accompanied by the follow‐up of local recurrence cases and analysis of tracking methods. Results Short‐term local control was superior for targets tracked with Synchrony than for targets localized with Xsight spine. There was no statistical difference for targets in the upper lung, but for targets in the lower lung Synchrony tracking was better. Small targets (less than 15 mL) were better controlled when Synchrony was used, but there was no difference for treatment volumes larger than 15 mL. Treatment failures were more likely in the lower lung and for small tumors localized with Xsight spine. Conclusions The local efficacy of CyberKnife treatment in lung cancer and lung metastases was influenced by image‐guided localization method, target location within the lung, and tumor volume.