title: Personalized assessment of kV cone beam computed tomography doses in image-guided radiotherapy of pediatric cancer patients.
abstract: OBJECTIVE
  To develop a quantitative method for the estimation of kV cone beam computed tomography (kVCBCT) doses in pediatric patients undergoing image-guided radiotherapy.
  
  
  METHODS
  Forty-two children were retrospectively analyzed in subgroups of different scanned regions: one group in the head-and-neck and the other group in the pelvis. Critical structures in planning CT images were delineated on an Eclipse treatment planning system before being converted into CT phantoms for Monte Carlo simulations. A benchmarked EGS4 Monte Carlo code was used to calculate three-dimensional dose distributions of kVCBCT scans with full-fan high-quality head or half-fan pelvis protocols predefined by the manufacturer. Based on planning CT images and structures exported in DICOM RT format, occipital-frontal circumferences (OFC) were calculated for head-and-neck patients using DICOMan software. Similarly, hip circumferences (HIP) were acquired for the pelvic group. Correlations between mean organ doses and age, weight, OFC, and HIP values were analyzed with SigmaPlot software suite, where regression performances were analyzed with relative dose differences (RDD) and coefficients of determination (R(2)).
  
  
  RESULTS
  kVCBCT-contributed mean doses to all critical structures decreased monotonically with studied parameters, with a steeper decrease in the pelvis than in the head. Empirical functions have been developed for a dose estimation of the major organs at risk in the head and pelvis, respectively. If evaluated with physical parameters other than age, a mean RDD of up to 7.9% was observed for all the structures in our population of 42 patients.
  
  
  CONCLUSIONS
  kVCBCT doses are highly correlated with patient size. According to this study, weight can be used as a primary index for dose assessment in both head and pelvis scans, while OFC and HIP may serve as secondary indices for dose estimation in corresponding regions. With the proposed empirical functions, it is possible to perform an individualized quantitative dose assessment of kVCBCT scans.
authors.affiliation: Beijing Key Lab of Medical Physics and Engineering, Peking University, Beijing, China.
authors.forename: Yibao
authors.initials: Y
authors.lastname: Zhang
authors.forename: Yulong
authors.initials: Y
authors.lastname: Yan
authors.forename: Ravinder
authors.initials: R
authors.lastname: Nath
authors.forename: Shanglian
authors.initials: S
authors.lastname: Bao
authors.forename: Jun
authors.initials: J
authors.lastname: Deng
mesh_terms: D000293:Adolescent; D000367:Age Factors; D049628:Body Size; D001835:Body Weight; D002648:Child; D002675:Child, Preschool; D054893:Cone-Beam Computed Tomography / Q000009:adverse effects / Q000379:methods*; D005260:Female; D006257:Head / Q000033:anatomy & histology / Q000528:radiation effects; D006801:Humans; D008297:Male; D009010:Monte Carlo Method; D009369:Neoplasms / Q000532:radiotherapy*; D058958:Organs at Risk / Q000033:anatomy & histology / Q000528:radiation effects*; D010388:Pelvis / Q000033:anatomy & histology / Q000528:radiation effects; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000517:prevention & control*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D012189:Retrospective Studies; D055815:Young Adult