title: Is integrated transit planar portal dosimetry able to detect geometric changes in lung cancer patients treated with volumetric modulated arc therapy?
abstract: BACKGROUND
  Geometric changes are frequent during the course of treatment of lung cancer patients. This may potentially result in deviations between the planned and actual delivered dose. Electronic portal imaging device (EPID)-based integrated transit planar portal dosimetry (ITPD) is a fast method for absolute in-treatment dose verification. The aim of this study was to investigate if ITPD could detect geometric changes in lung cancer patients.
  
  
  METHODS
  A total of 460 patients treated with volumetric modulated arc therapy (VMAT) following daily cone beam computed tomography (CT)-based setup were visually inspected for geometrical changes on a daily basis. Forty-six patients were subject to changes and had a re-CT and an adaptive treatment plan. The reasons for adaptation were: change in atelectasis (n = 18), tumor regression (n = 9), change in pleural effusion (n = 8) or other causes (n = 11). The ITPDs were calculated on both the initial planning CT and the re-CT and compared with a global gamma (γ) evaluation (criteria: 3%\3mm). A treatment fraction failed when the percentage of pixels failing in the radiation fields exceeded 10%. Dose-volume histograms (DVHs) were compared between the initial plan versus the plan re-calculated on the re-CT.
  
  
  RESULTS
  The ITPD threshold method detected 76% of the changes in atelectasis, while only 50% of the tumor regression cases and 42% of the pleural effusion cases were detected. Only 10% of the cases adapted for other reasons were detected with ITPD. The method has a 17% false-positive rate. No significant correlations were found between changes in DVH metrics and γ fail-rates.
  
  
  CONCLUSIONS
  This study showed that most cases with geometric changes caused by atelectasis could be captured by ITPD, however for other causes ITPD is not sensitive enough to detect the clinically relevant changes and no predictive power of ITPD was found.
authors.affiliation: a Department of Radiation Oncology (MAASTRO) , GROW - School for Oncology and Developmental Biology, Maastricht University Medical Centre , Maastricht , the Netherlands.
authors.forename: Lucas C G G
authors.initials: LC
authors.lastname: Persoon
authors.affiliation: a Department of Radiation Oncology (MAASTRO) , GROW - School for Oncology and Developmental Biology, Maastricht University Medical Centre , Maastricht , the Netherlands.
authors.forename: Mark
authors.initials: M
authors.lastname: Podesta
authors.affiliation: b Department of Medical Physics , Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Lone
authors.initials: L
authors.lastname: Hoffmann
authors.affiliation: a Department of Radiation Oncology (MAASTRO) , GROW - School for Oncology and Developmental Biology, Maastricht University Medical Centre , Maastricht , the Netherlands.
authors.forename: Abir
authors.initials: A
authors.lastname: Sanizadeh
authors.affiliation: a Department of Radiation Oncology (MAASTRO) , GROW - School for Oncology and Developmental Biology, Maastricht University Medical Centre , Maastricht , the Netherlands.
authors.forename: Lotte E J R
authors.initials: LE
authors.lastname: Schyns
authors.affiliation: a Department of Radiation Oncology (MAASTRO) , GROW - School for Oncology and Developmental Biology, Maastricht University Medical Centre , Maastricht , the Netherlands.
authors.forename: Ben-Max
authors.initials: BM
authors.lastname: de Ruiter
authors.affiliation: a Department of Radiation Oncology (MAASTRO) , GROW - School for Oncology and Developmental Biology, Maastricht University Medical Centre , Maastricht , the Netherlands.
authors.forename: Sebastiaan M J J G
authors.initials: SM
authors.lastname: Nijsten
authors.affiliation: b Department of Medical Physics , Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Ludvig P
authors.initials: LP
authors.lastname: Muren
authors.affiliation: a Department of Radiation Oncology (MAASTRO) , GROW - School for Oncology and Developmental Biology, Maastricht University Medical Centre , Maastricht , the Netherlands.|c Helmholtz Zentrum Dresden-Rossendorf , Dresden , Germany.|d OncoRay, National Center for Radiation Research in Oncology , Dresden , Germany.|e Department of Radiation Oncology , Medical Faculty and University Hospital Carl Gustav Carus, Technische Universität Dresden , Dresden , Germany.
authors.forename: Esther G C
authors.initials: EG
authors.lastname: Troost
authors.affiliation: a Department of Radiation Oncology (MAASTRO) , GROW - School for Oncology and Developmental Biology, Maastricht University Medical Centre , Maastricht , the Netherlands.|f Medical Physics Unit, Department of Oncology , McGill University , Montréal, Québec , Canada.
authors.forename: Frank
authors.initials: F
authors.lastname: Verhaegen
mesh_terms: D000368:Aged; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000532:radiotherapy; D054893:Cone-Beam Computed Tomography; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008297:Male; D016066:Pleural Effusion, Malignant / Q000000981:diagnostic imaging; D001261:Pulmonary Atelectasis / Q000000981:diagnostic imaging; D011874:Radiometry / Q000379:methods*; D061089:Radiotherapy, Image-Guided; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D055752:Small Cell Lung Carcinoma / Q000000981:diagnostic imaging / Q000532:radiotherapy