title: Assessment of target volume doses in radiotherapy based on the standard and measured calibration curves.
abstract: BACKGROUND
  In radiation treatments, estimation of the dose distribution in the target volume is one of the main components of the treatment planning procedure. To estimate the dose distribution, the information of electron densities is necessary. The standard curves determined by computed tomography (CT) scanner that may be different from that of other oncology centers. In this study, the changes of dose calculation due to the different calibration curves (HU-ρel) were investigated.
  
  
  METHODS
  Dose values were calculated based on the standard calibration curve that was predefined for the treatment planning system (TPS). The calibration curve was also extracted from the CT images of the phantom, and dose values were calculated based on this curve. The percentage errors of the calculated values were determined.
  
  
  METHODS
  The statistical analyses of the mean differences were performed using the Wilcoxon rank-sum test for both of the calibration curves.
  
  
  CONCLUSIONS
  The results show no significant difference for both of the measured and standard calibration curves (HU-ρel) in 6, 15, and 18 MeV energies. In Wilcoxon ranked sum nonparametric test for independent samples with P<0.05, the equality of monitor units for both of the curves to transfer 200 cGy doses to reference points was resulted. The percentage errors of the calculated values were lower than 2% and 1.5% in 6 and 15 MeV, respectively.
  
  
  CONCLUSIONS
  From the results, it could be concluded that the standard calibration curve could be used in TPS dose calculation accurately.
authors.affiliation: Department of Medical Physics and Biomedical Engineering, Faculty of Medicine, Tehran University of Medical Sciences, Tehran; Department of Radiology, Faculty of Paramedical, Mazandaran University of Medical Sciences, Sari, Iran.
authors.forename: Gholamreza Fallah
authors.initials: GF
authors.lastname: Mohammadi
authors.forename: Nader Riyahi
authors.initials: NR
authors.lastname: Alam
authors.forename: Hamed
authors.initials: H
authors.lastname: Rezaeejam
authors.forename: Tayyeb Allahverdi
authors.initials: TA
authors.lastname: Pourfallah
authors.affiliation: Department of Medical Physics and Biomedical Engineering, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Seyed Salman
authors.initials: SS
authors.lastname: Zakariaee
mesh_terms: D002138:Calibration; D006801:Humans; D009369:Neoplasms / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*