Extracranial stereotactic radiation therapy: set-up accuracy of patients treated for liver metastases.

PURPOSE Patients with liver metastases might benefit from high-dose conformal radiation therapy. A high accuracy of repositioning and a reduction of target movement are necessary for such an approach. The set-up accuracy of patients with liver metastases treated with stereotactic single dose radiation was evaluated. METHODS AND MATERIALS Twenty-four patients with liver metastases were treated with single dose radiation therapy on 26 occasions using a self-developed stereotactic frame. Liver movement was reduced by abdominal pressure. The effectiveness was evaluated under fluoroscopy. CT scans were performed on the planning day and directly before treatment. Representative reference marks were chosen and the coordinates were calculated. In addition, the target displacement was quantitatively evaluated after treatment. RESULTS Diaphragmal movement was reduced to median 7 mm (range: 3-13 mm). The final set-up accuracy of the body was limited to all of median 1.8 mm in latero-lateral direction (range: 0.3-5.0 mm) and 2.0 mm in anterior-posterior direction (0.8-3.8 mm). Deviations of the body in cranio-caudal direction were always less than the thickness of one CT slice (<5 mm). However, a repositioning was necessary in 16 occasions. The final target shift was median 1.6 mm (0.2-7.0 mm) in latero-lateral and 2.3 mm in anterior-posterior direction (0.0-6.3 mm). The median shift in cranio-caudal direction was 4.4 mm (0.0-10.0 mm). CONCLUSIONS In patients with liver metastases, a high set-up accuracy of the body and the target can be achieved. This allows a high-dose focal radiotherapy of these lesions. However, a control CT scan should be performed directly before therapy to confirm set-up accuracy and possibly prompt necessary corrections.