title: Dosimetric comparison of intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) in total scalp irradiation: a single institutional experience.
abstract: OBJECTIVE
  Total scalp irradiation (TSI) is a rare but challenging indication. We previously reported that non-coplanar intensity-modulated radiotherapy (IMRT) was superior to coplanar IMRT in organ-at-risk (OAR) protection and target dose distribution. This consecutive treatment planning study compared IMRT with volumetric-modulated arc therapy (VMAT).
  
  
  METHODS
  A retrospective treatment plan databank search was performed and 5 patient cases were randomly selected. Cranial imaging was restored from the initial planning computed tomography (CT) and target volumes and OAR were redelineated. For each patients, three treatment plans were calculated (coplanar/non-coplanar IMRT, VMAT; prescribed dose 50 Gy, single dose 2 Gy). Conformity, homogeneity and dose volume histograms were used for plan.
  
  
  RESULTS
  VMAT featured the lowest monitor units and the sharpest dose gradient (1.6 Gy/mm). Planning target volume (PTV) coverage and homogeneity was better in VMAT (coverage, 0.95; homogeneity index [HI], 0.118) compared to IMRT (coverage, 0.94; HI, 0.119) but coplanar IMRT produced the most conformal plans (conformity index [CI], 0.43). Minimum PTV dose range was 66.8% -88.4% in coplanar, 77.5%-88.2% in non-coplanar IMRT and 82.8%-90.3% in VMAT. Mean dose to the brain, brain stem, optic system (maximum dose) and lenses were 18.6, 13.2, 9.1, and 5.2 Gy for VMAT, 21.9, 13.4, 14.5, and 6.3 Gy for non-coplanar and 22.8, 16.5, 11.5, and 5.9 Gy for coplanar IMRT. Maximum optic chiasm dose was 7.7, 8.4, and 11.1 Gy (non-coplanar IMRT, VMAT, and coplanar IMRT).
  
  
  CONCLUSIONS
  Target coverage, homogeneity and OAR protection, was slightly superior in VMAT plans which also produced the sharpest dose gradient towards healthy tissue.
authors.affiliation: Department of Radiation Oncology, Faculty of Medicine, Martin Luther University Halle-Wittenberg, Halle, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Ostheimer
authors.affiliation: Department of Radiation Oncology, Faculty of Medicine, Martin Luther University Halle-Wittenberg, Halle, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Hübsch
authors.affiliation: Department of Radiation Oncology, Faculty of Medicine, Martin Luther University Halle-Wittenberg, Halle, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Janich
authors.affiliation: Department of Radiation Oncology, Faculty of Medicine, Martin Luther University Halle-Wittenberg, Halle, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Gerlach
authors.affiliation: Department of Radiation Oncology, Faculty of Medicine, Martin Luther University Halle-Wittenberg, Halle, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Vordermark
keywords: Angiosarcoma; Dosimetry; Intensity-modulated radiotherapy; Lymphoma of the scalp; Mycosis fungoides; Total scalp irradiation; Volumetric-modulated arc therapy