[Multimodal imaging during lung and abdominal stereotactic ablative radiotherapy: from cine MRI through 3D/4D CBCT to intrafractional kV verification]. / Multimodális képalkotás tüdõ- és hasi sztereotaxiás ablatív radioterápia során: a cine MRI-mérésektõl a 3D/4D CBCT-n át a kezelés alatti kV-os képi verifikációig.

Our aim was to present our treatment and verification protocols of linear accelerator-based lung and abdominal stereotactic ablative radiotherapy (SABR). During our treatments both the volumetric imaging (3D/4D CBCT/CT) and triggered kV intrafractional tumor motion control could be combined allowing a full control on the whole workflow. The most optimal kV directions from which the tumor is well detectable were defined. Tumor movements measured on cine MRI in treatment position correlated well with the ones on 4D CBCT, thus cine MRI is considered an excellent device to pre-select the appropriate image/treatment verification SABR protocol. In abdominal targets implanted markers and cine MRI are preferred due to limited image quality of CBCT with the current version. In selected lung SABR cases (≥8mm motion) the dose delivery of organs at risk (lungs - GTV, chest wall) could be reduced compared to free breathing conditions, however, the treatment time is at least two-folds higher.

Thermoplastic patient fixation: influence on chest wall and target motion during radiotherapy of lung cancer.

BACKGROUND AND PURPOSE: Several methods have been developed to reduce tumor motions and patient movements during radiotherapy of lung cancer. In this study, a multislice CT-based analysis was performed to examine the effect of a thermoplastic patient immobilization system on the chest wall and tumor motions. PATIENTS AND METHODS: Ten patients with stage II-IV lung cancer were enrolled into the study. According to tumor localization, five patients had peripheral, and five patients central lung cancer (T2-T4). In total, six series of measurements were made with a multislice CT scanner, both with and without mask fixation, in normal breathing, at maximal tidal volume inhalation, and at maximal tidal volume exhalation. RESULTS: Movements of chest wall, diaphragm and tumor, with and without mask, under different breathing conditions were registered. With the use of the immobilization system, no significant difference was found in diaphragmatic movements (mean deviation of diaphragm: 41.7-40.5 mm to the right, and 40.5-36.8 mm to the left side) and in tumor motions (mean deviation of tumor: 15.3-12.4 mm in craniocaudal, and 11.5-8.8 mm in posterolateral direction, mean medial deviation: 4.6-4.1 mm, mean lateral deviation: 7.2-5 mm). Significant differences were observed concerning tumor motions in anteroposterior direction (mean: 8.9-6.3 mm) and transverse chest movements in anteroposterior direction. CONCLUSION: Besides the advantage of optimal patient positioning, the movements of the bony chest wall can be considerably reduced by using the immobilization system. However, this fixation system has limitations concerning its suitability for minimizing tumor motions.