RESUMO
BACKGROUND: It can be difficult to perform CT guided biopsy of small pulmonary nodules especially if the position is behind a costa or close to the diaphragm and respiratory movements may hamper the procedure. During apneic oxygenation with a pulmonary standstill these movements can be hindered. METHODS: Six patients with decreased lung function and suspicious lung nodules are presented. Under general anesthesia including a muscle relaxant and a cuffed tube in the trachea CT guided biopsy was prepared. Just before the biopsy the ventilation mode was switched to a continuous positive airway pressure of 5-10 cm H2O, maintaining 100% oxygen delivery without ventilation. If the position of the lung nodule was inconvenient for biopsy the pressure was increased to up to 17 cm H2O to expand the lungs to a better biopsy position. After retrieving the biopsy controlled ventilation was re-established and a finishing control CT-scan was performed. Blood gas analyses were performed with few minutes interval. RESULTS: All biopsies were diagnostic. All patients survived the procedure with no major complications, but 3 patients developed pneumothorax. The length of apneic oxygenation was median 10 minutes (8-10 minutes). No major changes in vital parameters were observed, and in all patients the peripheral oxygen saturation was 100% throughout the procedure. The arterial oxygen tension rose to very high values and the lowest pH was 7.18. CONCLUSIONS: It is possible to perform lung biopsies in selected patients with decreased lung function during apneic oxygenation in at least 10 minutes in a safe way.
RESUMO
PURPOSE: To investigate the accuracy and potential limitations of MV image-based dynamic multileaf collimator (DMLC) tracking in a porcine model on a linear accelerator. METHODS AND MATERIALS: A thermo-expandable NiTi stent designed for kilovoltage (kV) X-ray visualization of lung lesions was inserted into the bronchia of three anaesthetized Göttingen minipigs. A four-dimensional computed tomography scan was used for planning a five-field conformal treatment with circular multileaf collimator (MLC) apertures. A 22.5 Gy single fraction treatment was delivered to the pigs. The peak-to-peak stent motion was 3 to 8 mm, with breathing periods of 1.2 to 4 s. Before treatment, X-ray images were used for image-guided setup based on the stent. During treatment delivery, continuous megavoltage (MV) portal images were acquired at 7.5 Hz. The stent was segmented in the images and used for continuous adaptation of the MLC aperture. Offline, the tracking error in beam's eye view of the treatment beam was calculated for each MV image as the difference between the MLC aperture center and the segmented stent position. The standard deviations of the systematic error Σ and the random error σ were determined and compared with the would-be errors for a nontracking treatment with pretreatment image-guided setup. RESULTS: Reliable stent segmentation was obtained for 11 of 15 fields. Segmentation failures occurred when image contrast was dominated by overlapping anatomical structures (ribs, diaphragm) rather than by the stent, which was designed for kV rather than MV X-ray visibility. For the 11 fields with reliable segmentation, Σ was 0.5 mm/0.4 mm in the two imager directions, whereas σ was 0.5 mm/1.1 mm. Without tracking, Σ and σ would have been 1.7 mm/1.4 mm and 0.8 mm/1.4 mm, respectively. CONCLUSION: For the first time, in vivo DMLC tracking has been demonstrated on a linear accelerator showing the potential for improved targeting accuracy. The study mimicked the envisioned patient workflow of future patient treatments. Clinical implementation of MV image-based tracking would require markers designed for MV visibility.
