(Wednesday, 7/17/2019) 9:30 AM - 10:00 AM
Room: Exhibit Hall | Forum 1
Purpose: To compare fractionated intracranial stereotactic radiotherapy (SRT) plans using a dynamic conformal arc (DCA) technique to those using a volumetric modulated arc (VMAT) technique developed with two different planning systems.
Methods: Clinical SRT plans were created for three patients using Brainlab iPlan RT Dose 4.5 (DCA plans) and Brainlab Cranial SRS 1.5 (VMAT plans) for a Varian Novalis TX with 120HD MLC leaves. Fractionation schemes included 9 Gy x 3 and 5 Gy x 5. The fusion of MRI and CT (1mm slices) and contouring of target and normal structures were performed using Brainlab Elements. GTVs/CTVs were contoured by the radiation oncologist and reviewed by a neurosurgeon, and PTV expansion was determined per case by both. One PTV was distant from organs at risk, and two PTVs were directly adjacent to critical normal structures. All plans included four or five arcs, and dose was calculated with Brainlab XVMC Monte Carlo dose algorithm with a 1mm dose grid and 2% statistical uncertainty. Plan parameters were recorded including PTV coverage, conformity index (CI), GTV minimum dose, GTV maximum dose, normal whole brain (WB) dose, total MUs, and adjacent OAR doses.
Results: Comparing VMAT and DCA plan parameters, for similar PTV coverage, the VMAT plans had a lower average CI (1.17 vs 1.41), higher GTV min dose (9% of prescription dose higher on average), lower normal WB V50%Rx (on average 67% of DCA plan), and lower adjacent normal structure doses in all cases.
Conclusion: VMAT plans created in Cranial SRS software were, expectedly, superior to DCA plans in terms of CI, GTV minimum dose, normal brain sparing, and adjacent critical structure sparing. However, a unique capability of Cranial SRS software allowed our facility to treat with VMAT technique on a Novalis TX machine without dose rate and gantry speed modulation.
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