[Stereotactic extracranial radiosurgery of liver tumors using respiratory gating--the method presentation]

Radiotherapy has not been widely accepted in the treatment of primary and secondary liver tumors due to its limited efficacy. This is caused by insufficient radiation doses and suboptimal techniques, which were used in the past. However, a present technological progress in radiotherapy has led to the application of modern and sophisticated radiation techniques into the treatment of liver tumors. The excellent example of such progress is stereotactic body radiation therapy (SBRT) (or radiosurgery), with respiratory gating. Such treatment method enables delivery of high radiation doses precisely to the tumor with sparing of surrounding critical tissues. It is possible by application of multiple beams and a narrow margin around the tumor considering its respiratory movement. This method of treatment may be applied under the condition of very precise radiological imaging and accurate patients' immobilization. The study presents a method of stereotactic body radiation therapy with respiratory gating introduced in the MSC Cancer Center and Institute of Oncology in Gliwice. The treatment criteria are as follows: patients in good general condition with inoperable primary and secondary tumors, 1-3 lesions with a maximal diameter of 6 cm. The fractionation schedule consists of three doses of 12 Gy delivered in weekly intervals to the total dose of 36 Gy normalized to the minimum in the PTV. Pre-treatment preparation procedures included: patient immobilization in a vacuum pillow, monitoring of respiratory cycle, the choice of respiratory phase suitable for irradiation and computed tomography (CT) for treatment planning. After preparation of treatment plan, the X-ray simulation is performed with verification of the position of isocenter. A respiratory tracking is performed during simulation. At the last stage, patient is immobilized at the couch of linear accelerator, the verification of the isocenter position using MV or kV images is performed and respiratory tracking is once again conducted. Irradiation delivered intermittently in the selected respiratory phase using automatical connection between respiratory tracking system and accelerator. The SBRT with respiratory gating appears to be a promising method of local treatment in patients with inoperable liver tumors.