Room: ePoster Forums
Purpose: Whether a 2.5 mm width multileaf collimator (MLC) and flattening filter free (FFF) photon beams offer an advantage over 5.0 mm width MLC and flattening filtered (FF) photon beams in the treatment of multitarget intracranial stereotactic radiosurgery, using volumetric-modulated arc therapy (VMAT).
Methods: Fifty three VMAT SRS patients with 132 intracranial targets (0.1-53.6 cmÂ³, mean = 5.6 Â± 9.1 cmÂ³) treated with 2.5 mm width MLC FFF beams were replanned, using the same optimization parameters, for a 5.0 mm width MLC with a FF beam. Plans were single isocenter and irradiated one to nine lesions. Dosimetric analysis consisted of comparisons of RTOG conformity and gradient indices, brain mean dose, monitor units (MU) and irradiation time.
Results: There was no statistically significant difference in conformity and gradient indices, brain mean dose, monitor units and irradiation time between the 2.5 mm width MLC 6 FFF versus 5.0 mm width MLC 6 FF. However, the conformity index difference was statistically significant (p << 0.05) in favor of the 5.0 mm width MLC 6 FF (1.05 Â± 0.15) over the 2.5 mm width MLC 10 FFF (1.14 Â± 0.18). Monitor units and irradiation time were also statistically significant with the 2.5 mm width MLC 10 FFF using more monitor units and having a shorter irradiation time (6422 Â± 2954; 248 Â± 73) than the 5.0 mm width MLC 6 FF (5136 Â± 2145; 374 Â± 100). Gradient index and brain mean dose were not statistically significant.
Conclusion: No significant dosimetric difference was observed between 2.5 mm width MLC 6 FFF versus 5.0 mm width MLC 6 FF. However, in comparison to the 2.5 mm width MLC 10 FFF, the 5.0 mm width MLC 6 FF provided better conformity index, used fewer monitor units and required longer irradiation time.