Integration of MR guided linear accelerator for treatment of multiple brain metastases with single-isocenter using stereotactic radiosurgery.

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Conference Proceeding

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Int J Radiat Oncol Biol Phys


Introduction: The purpose of study was to investigate the treatment planning capabilities and delivery accuracy for single isocenter multiple brain metastases treatment on an integrated 0.35T magnetic resonance imaging guided Linear Accelerator (MR-Linac) platform. Methods: The MR-Linac comprises a double-donut superconducting wide bore magnet with 0.345 T field strength and a ring-gantry mounted Linac system. The Linac has a 6X flattening filter free (FFF) beam with a dose rate up to 600 MU/min. The multileaf collimator (MLC) has a doublestack design to achieve a 4 mm spatial resolution which is half of the leaf width. Five patient plans with a total of eleven lesions were used to evaluate the dosimetric accuracy for intracranial treatment. Single-isocenter IMRT treatment plans using 10-15 coplanar beams were generated to treat the multiple metastases. The isocenter was placed at the geometric center among the lesions within each plan. All plans were calculated with 1 mm dose grid resolution using a fast Monte Carlo algorithm to a prescription dose of 16 or 18 Gy for each lesion. Plan quality was evaluated using the conformity index (CI), homogeneity index (HI) and gradient index (GI). Results: The average planning target volume was 4.8 cm3 (range 0.06-10.95 cm3). The conformity index, homogeneity index and gradient index of the plans were 1.26 ≤ 0.22, 1.22 ≤ 0.10, and 5.38 ≤ 1.44, respectively. The average absolute dose difference between measured and calculated dose to a MR compatible chamber volume was 1.64 ≤ 1.90% (range: -3.5% - 0.79%), and the percentage of points passing the 3%/1mm gamma criteria was 96.87 ≤ 1.53% (range: 93.50% - 99.00%). Conclusions: Our experience demonstrates that excellent plan quality and delivery accuracy was achievable on the MR-Linac for treating multiple brain metastases with a single isocenter.





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