Effects of flattening filter on dosimetry in fractionated stereotactic radiotherapy for brain metastases / 中国辐射卫生

ABSTRACT

@#<b>Objective</b> To investigate the dosimetric differences between volumetric modulated arc therapy (VMAT) with a flattening filter (FF) and flattening filter-free (FFF) VMAT in fractionated stereotactic radiotherapy for brain metastases. <b>Methods</b> Seventeen patients with brain metastases were divided into FF-VMAT group (VMAT plans with the FF mode) and FFF-VMAT group (VMAT plans with the FFF mode). The two groups were compared in terms of target volume dose parameters (<i>D</i>_98%, <i>D</i>_2% and <i>D</i>_mean), the conformal index (<i>CI</i>), the gradient index (<i>GI</i>), the gradient, normal brain tissue dose parameters (<i>V</i>_5Gy, <i>V</i>_10Gy, <i>V</i>_12Gy and <i>D</i>_mean), monitor units, and beam-on time. <b>Results</b> Compared with the FF-VMAT group, the FFF-VMAT group had significantly lower <i>GI</i> (3.33 ± 0.37 <i>vs</i> 3.27 ± 0.35, <i>P</i> = 0.001), a significantly lower gradient [(0.85 ± 0.20) cm <i>vs</i> (0.84 ± 0.19) cm, <i>P</i> = 0.002], a significantly shorter beam-on time [(177.05 ± 62.68) s <i>vs</i> (142.71 ± 34.59) s, <i>P</i> = 0.001], and significantly higher <i>D</i>_2% [(65.69 ± 2.15) Gy <i>vs</i> (66.99 ± 2.03) Gy, <i>P</i> = 0.001] and <i>D</i>_mean [(58.77 ± 1.60) Gy <i>vs</i> (59.95 ± 1.43) Gy, <i>P</i> <0.001]. There were no significant differences in the <i>CI</i>, the<i> D</i>_98%of the target volume, the <i>V</i>_5Gy, <i>V</i>_10Gy, <i>V</i>_12Gy and <i>D</i>_mean of the normal brain tissue, and monitor units between FFF-VMAT and FF-VMAT. <b>Conclusion</b> FFF-VMAT can better protect the normal tissue around the target volume, reduce the beam-on time, and improve treatment efficiency.