Objective: Advanced techniques such as volumetric-modulated arc therapy (VMAT) may reduce radiation damage and improve the quality of life for patients.We performed a study comparing dose distributions to the planning target volumes(PTVs) and other organs at risk (OARs) of intensity-modulated radiotherapy (IMRT),coplanar VMAT (coVMAT), and non-coplanar VMAT (ncVMAT).
Patients and methods: 13 patients with GBM who had undergone postoperative radiotherapy were enrolled. Three plans for each patient were created, namely, IMRT, coVMAT, and ncVMAT. Prescription doses and normal-tissue constraints were identical for these three plans. The dosimetric differences of target dose distribution, conformity index (CI), homogeneity index (HI), the gradient index (GI), dose of OARs, monitor units (MUs) and beam-on times among these three plans were investigated.
Results: These three techniques resulted in comparable maximum, minimum, and mean PTV doses. Small but insignificant differences were observed in GI,CI, and HI. Compared with IMRT, VMAT plans showed statistically significant reductions in the mean doses to the optic chiasm (P < 0.05). Compared with IMRT, VMAT techniques significantly reduced the number of MUs and less beam-on time than IMRT techniques (P ＜ 0.05). However, calculation times were significantly longer for ncVMAT and coVMAT plans at 12 and 12.3 min, versus 2.6 min for IMRT. Our study showed that IMRT or VMAT planning is feasible and efficient for patients with GBM.Compared to IMRT plans, ncVMAT or coVMAT plans showed similar PTV coverage and comparable OARs sparing. VMAT plans significantly reduces the mean doses to the optic chiasm than IMRT plans.
Conclusion: There was no obvious superiority of ncVMAT over coVMAT in target coverage and sparing of OARs.Compared with IMRT, VMAT techniques significantly reduced the number of MUs and beam-on time but extended the calculation times.
Keywords: Dosimetry; Glioblastoma; IMRT; Noncoplanar; VMAT.
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