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Flattening Filter Free Photon Beams for Stereotactic Radiosurgery of Trigeminal Neuralgia: A Plan Comparison Study

D Mynampati1*, K Jeong2 , M Garg3 , R Yaparpalvi4 , W Tome5 Montefiore Medical Center, Bronx, NY,


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Dosimetric comparison of Stereotactic Radiosurgery (SRS) plans of Trigeminal Neuralgia (TN) using TrueBeam 06MV, 06FFF and 10FFF photon beams.
Methods: This study includes all eight TN patients we treated with SRS in last two years. Our present SRS technique to treat TN involves Brainlab, SRS frame, iplan planning system and, 4mm cone, with TrueBeam 06MV photon beam. Our SRS plans consists seven arcs of 100 degrees length with 140 degrees couch spread. Dose prescription is to deliver 85Gy to Isocenter. All eight 06MV SRS plans recomputed with Brainlab, iplan 6FFF and 10FFF beam profiles separately. Dosimetric parameters used for plan comparison are Total volume receiving 40Gy (V40Gy) and 20Gy (V20Gy). Volume of Brainstem (BS) receiving 20Gy (BSV20Gy), BS’s 12Gy Volume (BSV12Gy), dose to 0.03cc of BS (BSD0.03cc) and Total Monitor units (MU). Required photon beam data for SRS cone profiles were measured using Stereotactic diode (IBA SFD) and EBT films. Our scatter, PDD and profiles parameters are comparable to published data.
Results: Our 4mm Cone scatter factors for 06MV, 6FFF and 10FFF photon beams are 0.622,0.672 and 0.552 respectively. For all three photon beams, FWHM of 4mm Cone profiles at 7.5cm depth and SSD 92.5cm is 3.9mm. Measured penumbra of 4mm cone profile of 06MV, 6FFF and 10FFF are 1.0mm, 1.0 mm and 1.2mm. Mean V40Gy of 6MV, 6FFF and 10FFF plans are 0.068, 0.059 and 0.068. Similarly, mean V20Gy are 0.24,0.204and 0.25. Mean BS12Gy are 0.026cc,0.016cc and 0.031cc. Mean BS20Gy are 0.003cc, 0.001cc and 0.003cc. D0.03cc of BS are 11.74Gy, 10.42Gy and 12.35Gy. Average MUs (dose rate) for 06MV, 06FFF and 10FFF plans are 21474(600MU/min), 21518(1400MU/min) and 22543(2400MU/min)
Conclusion: Dosimetrically all three photon beam plans are comparable. However, 6FFF beam have slight dosimetric advantage with reduced beam on time.


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