title: Quasi-VMAT in high-grade glioma radiation therapy.
abstract: OBJECTIVE
  To compare a quasi-volumetric modulated arc therapy (qVMAT) with three-dimensional conformal radiation therapy (3D-CRT) and intensity-modulated radiation therapy (IMRT) for the treatment of high-grade gliomas. The qVMAT technique is a fast method of radiation therapy in which multiple equispaced beams analogous to those in rotation therapy are radiated in succession.
  
  
  METHODS
  This study included 12 patients with a planning target volume (PTV) that overlapped at least one organ at risk (OAR). 3D-CRT was planned using 2-3 non-coplanar beams, whereby the field-in-field technique (FIF) was used to divide each field into 1-3 subfields to shield the OAR. The qVMAT strategy was planned with 15 equispaced beams and IMRT was planned using 9 beams with a total of 80 segments. Inverse planning for qVMAT and IMRT was performed by direct machine parameter optimization (DMPO) to deliver a homogenous dose distribution of 60 Gy within the PTV and simultaneously limit the dose received by the OARs to the recommended values. Finally, the effect of introducing a maximum dose objective (max. dose < 54 Gy) for a virtual OAR in the form of a 0.5 cm ring around the PTV was investigated.
  
  
  RESULTS
  The qVMAT method gave rise to significantly improved PTV95% and conformity index (CI) values in comparison to 3D-CRT (PTV95% = 90.7 % vs. 82.0 %; CI = 0.79 vs. 0.74, respectively). A further improvement was achieved by IMRT (PTV95% = 94.4 %, CI = 0.78). In qVMAT and IMRT, the addition of a 0.5 cm ring around the PTV produced a significant increase in CI (0.87 and 0.88, respectively), but dosage homogeneity within the PTV was considerably reduced (PTV95% = 88.5 % and 92.3 %, respectively). The time required for qVMAT dose delivery was similar to that required using 3D-CRT.
  
  
  CONCLUSIONS
  These findings suggest that qVMAT should be preferred to 3D-CRT for the treatment of high-grade gliomas. The qVMAT method could be applied in hospitals, for example, which have limited departmental resources and are not equipped with systems capable of VMAT delivery.
authors.affiliation: Department of Radio-Oncology, Regional Oncological Hospital, via Jenner, 09121, Cagliari, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Fadda
authors.forename: G
authors.initials: G
authors.lastname: Massazza
authors.forename: S
authors.initials: S
authors.lastname: Zucca
authors.forename: S
authors.initials: S
authors.lastname: Durzu
authors.forename: G
authors.initials: G
authors.lastname: Meleddu
authors.forename: M
authors.initials: M
authors.lastname: Possanzini
authors.forename: P
authors.initials: P
authors.lastname: Farace
mesh_terms: D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000175:diagnosis / Q000532:radiotherapy*; D005260:Female; D005910:Glioma / Q000175:diagnosis / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D016896:Treatment Outcome
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