title: Verification of patient-specific dose distributions in proton therapy using a commercial two-dimensional ion chamber array.
abstract: OBJECTIVE
  The purpose of this study was to determine whether a two-dimensional (2D) ion chamber array detector quickly and accurately measures patient-specific dose distributions in treatment with passively scattered and spot scanning proton beams.
  
  
  METHODS
  The 2D ion chamber array detector MatriXX was used to measure the dose distributions in plastic water phantom from passively scattered and spot scanning proton beam fields planned for patient treatment. Planar dose distributions were measured using MatriXX, and the distributions were compared to those calculated using a treatment-planning system. The dose distributions generated by the treatment-planning system and a film dosimetry system were similarly compared.
  
  
  RESULTS
  For passively scattered proton beams, the gamma index for the dose-distribution comparison for treatment fields for three patients with prostate cancer and for one patient with lung cancer was less than 1.0 for 99% and 100% of pixels for a 3% dose tolerance and 3 mm distance-to-dose agreement, respectively. For spot scanning beams, the mean (+/- standard deviation) percentages of pixels with gamma indices meeting the passing criteria were 97.1% +/- 1.4% and 98.8% +/- 1.4% for MatriXX and film dosimetry, respectively, for 20 fields used to treat patients with prostate cancer.
  
  
  CONCLUSIONS
  Unlike film dosimetry, MatriXX provides not only 2D dose-distribution information but also absolute dosimetry in fractions of minutes with acceptable accuracy. The results of this study indicate that MatriXX can be used to verify patient-field specific dose distributions in proton therapy.
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA. barjomandy@mdanderson.org
authors.forename: Bijan
authors.initials: B
authors.lastname: Arjomandy
authors.forename: Narayan
authors.initials: N
authors.lastname: Sahoo
authors.forename: George
authors.initials: G
authors.lastname: Ciangaru
authors.forename: Ronald
authors.initials: R
authors.lastname: Zhu
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Song
authors.forename: Michael
authors.initials: M
authors.lastname: Gillin
mesh_terms: D005373:Film Dosimetry / Q000379:methods; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D061766:Proton Therapy; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D011878:Radiotherapy / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D011522:Protons
chemical_list: D011522:Protons