title: Kilovoltage imaging doses in the radiotherapy of pediatric cancer patients.
abstract: OBJECTIVE
  To investigate doses induced by kilovoltage cone-beam computed tomography (kVCBCT) to pediatric cancer patients undergoing radiotherapy, as well as strategies for dose reduction.
  
  
  METHODS
  An EGS4 Monte Carlo code was used to calculate three-dimensional dose deposition due to kVCBCT on 4 pediatric cancer patients. Absorbed doses to various organs were analyzed for both half-fan and full-fan modes. Clinical conditions, such as distance from organ at risk (OAR) to CBCT field border, kV peak energy, and testicular shielding, were studied.
  
  
  RESULTS
  The mean doses induced by one CBCT scan operated at 125 kV in half-fan mode to testes, liver, kidneys, femoral heads, spinal cord, brain, eyes, lens, and optical nerves were 2.9, 4.7, 7.7, 10.5, 8.8, 7.6, 7.7, 7.8, and 7.2 cGy, respectively. Increasing the distances from OARs to CBCT field border greatly reduced the doses to OARs, ranging from 33% reduction for spinal cord to 2300% reduction for testes. As photon beam energy increased from 60 to 125 kV, the dose increase due to kVCBCT ranged from 170% for lens to 460% for brain and spinal cord. A testicular shielding made of 1-cm cerrobend could reduce CBCT doses down to 31%, 51%, 68%, and 82%, respectively, for 60, 80, 100, and 125 kV when the testes lay within the CBCT field.
  
  
  CONCLUSIONS
  Generally speaking, kVCBCT deposits much larger doses to critical structures in children than in adults, usually by a factor of 2 to 3. Increasing the distances from OARs to CBCT field border greatly reduces doses to OARs. Depending on OARs, kVCBCT-induced doses increase linearly or exponentially with photon beam energy. Testicular shielding works more efficiently at lower kV energies. On the basis of our study, it is essential to choose an appropriate scanning protocol when kVCBCT is applied to pediatric cancer patients routinely.
authors.affiliation: Department of Therapeutic Radiology, Yale University, New Haven, CT, USA. jun.deng@yale.edu
authors.forename: Jun
authors.initials: J
authors.lastname: Deng
authors.forename: Zhe
authors.initials: Z
authors.lastname: Chen
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Roberts
authors.forename: Ravinder
authors.initials: R
authors.lastname: Nath
mesh_terms: D002648:Child; D002675:Child, Preschool; D054893:Cone-Beam Computed Tomography / Q000009:adverse effects* / Q000379:methods; D004806:Ependymoma / Q000000981:diagnostic imaging / Q000532:radiotherapy; D005260:Female; D006801:Humans; D015192:Infratentorial Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D008297:Male; D009010:Monte Carlo Method; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D058958:Organs at Risk / Q000528:radiation effects*; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000517:prevention & control; D011835:Radiation Protection / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000009:adverse effects / Q000379:methods*; D012186:Retroperitoneal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D012208:Rhabdomyosarcoma / Q000000981:diagnostic imaging / Q000532:radiotherapy; D013737:Testis / Q000528:radiation effects