Feasibility of constant dose rate VMAT in the treatment of nasopharyngeal cancer patients

Abstract

PurposeTo investigate the feasibility of constant dose rate volumetric modulated arc therapy (CDR-VMAT) in the treatment of nasopharyngeal cancer (NPC) patients and to introduce rotational arc radiotherapy for linacs incapable of dose rate variation.Materials and methodsTwelve NPC patients with various stages treated previously using variable dose rate (VDR) VMAT were enrolled in this study. CDR-VMAT, VDR-VMAT and mutlicriteria optimization (MCO) VMAT plans were generated for each patient on RayStation treatment planning system with identical objective functions and the dosimetric differences among these three planning schemes were evaluated and compared. Non dosimetric parameters of optimization time, delivery time and delivery accuracy were also evaluated.ResultsThe planning target volume of clinical target volume (PTV-CTV) coverage of CDR-VMAT was a bit inferior to those of VDR- and MCO-VMAT. The V93 (p = 0.01) and V95 (percent volume covered by isodose line) (p = 0.04) for CDR-VMAT, VDR-VMAT and MCO-VMAT were 98.74% ± 0.31%, 99.76% ± 0.16%, 99.38% ± 0.43%, and 98.40% ± 0.48%, 99.53% ± 0.28%, 99.07% ± 0.52%, respectively. However, the CDR-VMAT showed a better dose homogeneity index (HI) (p = 0.01) in PTV-CTV. No significant difference in other target coverage parameters was observed. There was no significant difference in OAR sparing among these three planning schemes except for a higher maximum dose (Dmax) on the brainstem for CDR-VMAT. The brainstem Dmax of CDR-VMAT, VDR-VMAT and MCO-VMAT were 54.26 ± 3.21 Gy, 52.19 ± 1.65 Gy, and 52.79 ± 4.77 Gy, respectively. The average delivery time (p < 0.01) and the average percent γ passing rates (p = 0.02) of CDR-VMAT, VDR-VMAT and MCO-VMAT were 7.01 ± 0.43 min, 4.75 ± 0.07 min, 4.01 ± 0.28 min, and 95.75% ± 2.57%, 97.65% ± 1.45%, 97.36% ± 2.45%, respectively.ConclusionCDR-VMAT offers an additional option of rotational arc radiotherapy for linacs incapable of dose rate variation with a lower initial cost. Its plan quality was acceptable but should be thoroughly checked compared with VDR-VMAT and MCO-VMAT in the treatment of NPC.

Is volumetric modulated arc therapy with constant dose rate a valid option in radiation therapy for head and neck cancer patients?

“…Two investigated its role in the pelvic area 13,14 and one in nasopharyngeal cancer. 15 Comparing observations by Yu et al 15 with the present series is difficult because the former focused only on the nasopharyngeal area, while our series only included patients with oropharyngeal, hypopharyngeal and laryngeal cancer. Consequently, in the study by Yu et al, 15 some OARs such as the brainstem and parotids were closer to the PTV than in the present investigation so that maximum and mean doses were higher.…”

“…Present results support using CDR-VMAT for head and neck radiotherapy as it emerged as a valid option when a dedicated linear accelerator is not available for VMAT therapy with variable dose-rates and gantry velocities. To date, few studies have focused on CDR-VMAT in treatment planning [11][12][13][14][15] with only three assessing the implications of using it in clinical practice. Two investigated its role in the pelvic area 13,14 and one in nasopharyngeal cancer.…”

Assessment of volumetric-modulated arc therapy for constant and variable dose rates

“…Similar results were reported for nasopharyngeal cancer, in which 12 previously treated patients were used for comparison between VDR, MCO, and CDR of 400 MU/min, results of this study showed no significant dosimetric differences between MCO, CDR and VDR plans. [ 15 ]…”

“…It has been previously demonstrated that VDR VMAT is superior than CDR in terms of delivery time and number of MUs,[ 15 21 22 ] yet with significantly lower delivery time than IMRT. [ 11 ] This study demonstrated consistent increase of MUs as the constant dose rate increased.…”

“…Recently published work by Yu et al . [ 15 ] compared CDR-based, VDR-based VMAT plans with multicriteria optimization (MCO) VMAT plans in nasopharyngeal cancer patients using Raystation TPS. In their comparison, they selected 400 MU/min as its CDR, yet did not mention rationale to selecting such value.…”