END-TO-END VALIDATION OF TREATMENTS OF MULTIPLE METASTASIS WITH RADIOSURGERY USING SINGLE ISOCENTER AND ANTHROPOMORPHIC PHANTOMA

Introduction: Technological advances in radiotherapy allow treatments with higher doses in the target volumes and saving more healthy tissues, which proves to be efficient for central nervous system disease control. The use of VMAT with mMLC for the treatment of metastases makes the procedure faster and ensures greater reproducibility. Objective: To validate multiple brain metastasis treatments with the use of VMAT and single isocenter. Methodology: Ten acrylic rods were attached to an anthropomorphic skull-shaped phantom filled with bolus. These rods served to simulate intracranial lesions and to fix the PinPoint 3D Ionization Chamber (PTW 30016, 0.016cc). Using immobilization supports (mask, base and head support) the phantom was submitted to a tomography with radiosurgery protocol. A dose of 24Gy was prescribed in 8 lesions, 9Gy in one lesion and 2Gy in another. The latter served to evaluate the modulation capacity of the beam at low doses. Absolute dose measurements were made with the ionization chamber and beam fluence measurements with Dosimetry Portal. The positioning of the phantom was verified by planar images and CBCT. Results: The doses obtained from the IC measurements differed between 0.1% and 5.8%, with standard deviations of up to 2.9 cGy, and the analysis of the gamma index values by the PD passed above 95.7% (γ <1, 3% DTA / 3mm). Conclusion: Despite the differences found, the end-to-end evaluation result validated the protocol with acceptable values, based on the literature, considering the test uncertainties as well as the measurement instruments used.