title: Evaluation of In Vivo Volumetric Dosimetry for Prostate Cancer Using Electronic Portal Imaging Device.
abstract: Volumetric modulated arc therapy (VMAT) is capable of acquiring projection images using electronic portal imaging device (EPID). Commercial EPID-based dosimetry software, dosimetry check (DC), allows in vivo dosimetry using projection images. The purpose of this study was to evaluate in vivo dosimetry for prostate cancer using VMAT.
  
  
  
  VMAT plans were generated for eight patients with prostate cancer using treatment planning system (TPS), and patient quality assurances (QAs) were carried out with phantom. We analyzed five plans as phantom study and five plans as patient study. Projection images were acquired during VMAT delivery. DC converted acquired images into fluence images and used a pencil beam algorithm to calculate dose distributions delivered on the CT images of the phantom and the patients. We evaluated isocenter point doses and gamma analysis in both studies and dose indexes of planning target volume (PTV), bladder and rectum in patient study.
  
  
  
  Dose differences at the isocenter were less than a criterion in both studies. Pass rates of the gamma analysis were less than a criterion by two plans in the phantom study. Dose indexes of reconstructed distribution were lower than original plans and standard deviations of PTV in reconstructed distribution were larger than original plans. The errors were caused by some issues, such as the commissioning of DC, variations in patient anatomy, and patient positioning.
  
  
  
  The method was feasible to non-invasively perform in vivo dose evaluation for prostate cancer using VMAT.
authors.affiliation: Department of Radiology, University of Tokyo Hospital.
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Imae
authors.forename: Shigeharu
authors.initials: S
authors.lastname: Takenaka
authors.forename: Yuuichi
authors.initials: Y
authors.lastname: Watanabe
authors.forename: Yukari
authors.initials: Y
authors.lastname: Okano
authors.forename: Makoto
authors.initials: M
authors.lastname: Nedu
authors.forename: Shigeki
authors.initials: S
authors.lastname: Saegusa
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Takeuchi
authors.forename: Keiichi
authors.initials: K
authors.lastname: Yano
authors.forename: Akihiro
authors.initials: A
authors.lastname: Haga
authors.forename: Kenshirou
authors.initials: K
authors.lastname: Shiraishi
authors.forename: Hideomi
authors.initials: H
authors.lastname: Yamashita
authors.forename: Keiichi
authors.initials: K
authors.lastname: Nakagawa
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D000072232:Radiation Dosimeters; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D014057:Tomography, X-Ray Computed