Abstract
The purpose of this study was to compare dosimetric and radiobiological parameters of treatment plans using coplanar and noncoplanar beam arrangements in patients with fronto‐temporal high‐grade glioma (HGG) generated for intensity‐modulated radiotherapy (IMRT) or volumetric‐modulated arc therapy (VMAT). Ten cases of HGG overlapping the optic apparatus were selected. Four separate plans were created for each case: coplanar IMRT, noncoplanar IMRT (ncIMRT), VMAT, and noncoplanar VMAT (ncVMAT). The prescription dose was 60 Gy in 30 fractions. Dose‐volume histograms and equivalent uniform doses (EUD) for planning target volumes (PTVs) and organs at risk (OARs) were generated. The four techniques resulted in comparable mean, minimum, maximum PTV doses, and PTV EUDs (p≥0.33). The mean PTV dose and EUD averaged for all techniques were 59.98 Gy (Standard Deviation (SD)±0.15) and 59.86 Gy (SD±0.27). Noncoplanar IMRT significantly reduced contralateral anterior globe EUDs (6.7 Gy versus 8.2 Gy, p=0.05), while both ncIMRT and ncVMAT reduced contralateral retina EUDs (16 Gy versus 18.8 Gy, p=0.03). Noncoplanar techniques resulted in lower contralateral temporal lobe dose (22.2 Gy versus 24.7 Gy). Compared to IMRT, VMAT techniques required fewer monitor units (755 vs. 478, p≤0.001) but longer optimization times. Treatment delivery times were 6.1 and 10.5 minutes for coplanar and ncIMRT versus 2.9 and 5.0 minutes for coplanar and ncVMAT. In this study, all techniques achieved comparable target coverage. Superior sparing of contralateral optic structures was seen with ncIMRT. The VMAT techniques reduced treatment delivery duration but prolonged plan optimization times, compared to IMRT techniques. Technique selection should be individualized, based on patient‐specific clinical and dosimetric parameters.PACS number: 87
Highlights
As our understanding of the biology and pharmacogenetics of central nervous system (CNS) malignancies evolves, therapies have advanced to become more efficacious
In ad dition, intensity-modulated radiotherapy (IMRT) decreased normal tissue doses, especially in cases where the target abutted critical structures such as the optic nerves and the brainstem.[4,5,6,7] Others have shown the feasibility of using coplanar and noncoplanar IMRT techniques to treat patients with high-grade gliomas, but data on direct dosimetric comparison between the two techniques are lacking.[5,8,9,10] In a recent publication comparing the use of coplanar volumetric-modulated arc therapy (VMAT) with coplanar fixed-field IMRT, VMAT achieved equal or better target coverage, with improved sparing of normal organs at risk.[11]
Small but significant differences were observed in conforma lity indices (CI), with improved CI noted in VMAT plans (IMRT 0.88 and noncoplanar IMRT (ncIMRT) 0.89 versus VMAT 0.917 and noncoplanar VMAT (ncVMAT) 0.923, p < 0.05), while homogeneity indices were similar across techniques evaluated (HI 0.99 for all techniques)
Summary
As our understanding of the biology and pharmacogenetics of central nervous system (CNS) malignancies evolves, therapies have advanced to become more efficacious. The observation that coplanar techniques irradiate OARs such as the optic chiasm and optic nerves to adequately treat adjacent PTVs led to the hypothesis that techniques that involve noncoplanar beam arrangements may decrease doses to these same critical structures.[11]. As a result, this dosimetric study was conducted to compare four treatment planning methods: coplanar IMRT (IMRT), noncoplanar IMRT (ncIMRT), coplanar VMAT (VMAT), and noncoplanar VMAT (ncVMAT) In ad dition, IMRT decreased normal tissue doses, especially in cases where the target abutted critical structures such as the optic nerves and the brainstem.[4,5,6,7] Others have shown the feasibility of using coplanar and noncoplanar IMRT techniques to treat patients with high-grade gliomas, but data on direct dosimetric comparison between the two techniques are lacking.[5,8,9,10] In a recent publication comparing the use of coplanar volumetric-modulated arc therapy (VMAT) with coplanar fixed-field IMRT, VMAT achieved equal or better target coverage, with improved sparing of normal organs at risk.[11]
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