Dosimetric Comparison of 6 MV Flattening Filter Free and 6 MV Stereotactic Radiosurgery Beam Using 4 mm Conical Collimator for Trigeminal Neuralgia Radiosurgery

  • Mhatre, Vaibhav R (Department of Radiation Oncology and Neurosurgery, Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute) ;
  • Chadha, Pranav (Department of Radiation Oncology and Neurosurgery, Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute) ;
  • Kumar, Abhaya P (Department of Radiation Oncology and Neurosurgery, Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute) ;
  • Talapatra, Kaustav (Department of Radiation Oncology and Neurosurgery, Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute)
  • Received : 2018.06.14
  • Accepted : 2018.08.07
  • Published : 2018.09.30


Background: The purpose of our study was to compare the dosimetric advantages of Flattening filter free (FFF) beams for trigeminal neuralgia patients using 4 mm conical collimators over previously treated patients with 6 MV SRS beam. Materials and Methods: A retrospective study was conducted for 5 TN patients who had been previously treated at our institution using frame-based, LINAC-based stereotactic radiosurgery (SRS) on Novalis Tx using 6 MV SRS beam were replanned on 6X FFF beams on Edge Linear accelerator with same beam angles and dose constraints using 4 mm conical collimator. The total number of monitor units along with the beam on time was compared for both Edge and Novalis Tx by redelivering the plans in QA mode of LINAC to compare the delivery efficiency. Plan quality was evaluated by homogeneity index (HI) and Paddick gradient index (GI) for each plan. We also analyzed the doses to brainstem and organ at risks (OARs). Results and Discussion: A 28% beam-on time reduction was achieved using 6X FFF when compared with 6X SRS beam of Novalis Tx. A sharp dose fall off with gradient index value of $3.4{\pm}0.27$ for 4 mm Varian conical collimator while $4.17{\pm}0.20$ with BrainLab cone. Among the 5 patients treated with a 4 mm cone, average maximum brainstem dose was 10.24 Gy for Edge using 6X FFF and 14.28 Gy for Novalis Tx using 6X SRS beam. Conclusion: The use of FFF beams improves delivery efficiency and conical collimator reduces dose to OAR's for TN radiosurgery. Further investigation is warranted with larger sample patient data.


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