Dosimetric Comparison of Fractionated Stereotactic Radiotherapy Plans With And Without Flattening Filter Beams of 6 MV And 10 MV Beams

It is necessary to understand the importance of different energies in Fractionated Stereotactic Radiotherapy (FSRT) plans for better outcome. The study objective is to compare FSRT plans with Flattening Filter (FF) and Flattening Filter Free (FFF) beams. Twelve patients with primary Brain Metastasis (BM), were selected and given 25 Gy in five fractions for which 6FF beams were angled in double arc. The Planning Target Volume (PTV) and Organs at Risk (OARs) were assessed using dosimetric indices after each plan was replanned with 6 FFF, 10 FF, and 10 FFF energies. Treatment time (TT) and Monitor Units (MUs) were also compared. Additionally, we compared portal dosimetry for dose agreement across all plans using the gamma analysis criterion. PTV parameters of created plans showed better values when compared to 6 FF plans, where the most significant is with FFF plans which include D98%, D80%, D2%, D50% and Dose Gradient Index values of 6FFF plans. Among OARs, the most significant is the V10 value of (Brain-PTV) as (46.77±43.9) and maximum dose values of optic chiasm, brainstem, and left lens in 6FFF plans. Among technical parameters, the 6FFF plan showed significant TT value of (3.06±1.0) with p-value 4.13E-05. Better gamma analysis passing rates were achieved with FFF beams. Linear accelerator-based FSRT delivery of BM using 6 FFF beam results in better dosimetric indices, OAR sparing, fastest treatment delivery, and energy conservation with reduced peripheral and out-of-field dose for higher treatment modalities like Rapid arc.