title: In vivo portal dosimetry for head-and-neck VMAT and lung IMRT: linking γ-analysis with differences in dose-volume histograms of the PTV.
abstract: OBJECTIVE
  To relate the results of γ-analysis and dose-volume histogram (DVH) analysis of the PTV for detecting dose deviations with in vivo dosimetry for two treatment sites.
  
  
  METHODS
  In vivo 3D dose distributions were reconstructed for 722 fractions of 200 head-and-neck (H&N) VMAT treatments and 183 fractions of 61 lung IMRT plans. The reconstructed and planned dose distributions in the PTV were compared using (a) the γ-distribution and (b) the differences in D2, D50 and D98 between the two dose distributions. Using pre-defined tolerance levels, all fractions were classified as deviating or not deviating by both methods. The mutual agreement, the sensitivity and the specificity of the two methods were compared.
  
  
  RESULTS
  For lung IMRT, the classification of the fractions was nearly identical for γ- and DVH-analyses of the PTV (94% agreement) and the sensitivity and specificity were comparable for both methods. Less agreement (80%) was found for H&N VMAT, while γ-analysis was both less sensitive and less specific.
  
  
  CONCLUSIONS
  DVH- and γ-analyses perform nearly equal in finding dose deviations in the PTV for lung IMRT treatments; for H&N VMAT treatments, DVH-analysis is preferable. As a result of this study, a smooth transition to using DVH-analysis clinically for detecting in vivo dose deviations in the PTV is within reach.
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands. Electronic address: r.rozendaal@nki.nl.
authors.forename: Roel Arthur
authors.initials: RA
authors.lastname: Rozendaal
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Mijnheer
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
authors.forename: Marcel
authors.initials: M
authors.lastname: van Herk
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
authors.forename: Anton
authors.initials: A
authors.lastname: Mans
mesh_terms: D005720:Gamma Rays; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: DVH-analysis; EPID; In vivo dosimetry; Portal dosimetry; QA; γ-Analysis