title: Testicular doses in image-guided radiotherapy of prostate cancer.
abstract: OBJECTIVE
  To investigate testicular doses contributed by kilovoltage cone-beam computed tomography (kVCBCT) during image-guided radiotherapy (IGRT) of prostate cancer.
  
  
  METHODS
  An EGS4 Monte Carlo code was used to calculate three-dimensional dose distributions from kVCBCT on 3 prostate cancer patients. Absorbed doses to various organs were compared between intensity-modulated radiotherapy (IMRT) treatments and kVCBCT scans. The impact of CBCT scanning mode, kilovoltage peak energy (kVp), and CBCT field span on dose deposition to testes and other organs was investigated.
  
  
  RESULTS
  In comparison with one 10-MV IMRT treatment, a 125-kV half-fan CBCT scan delivered 3.4, 3.8, 4.1, and 5.7 cGy to the prostate, rectum, bladder, and femoral heads, respectively, accounting for 1.7%, 3.2%, 3.2%, and 8.4% of megavoltage photon dose contributions. However, the testes received 2.9 cGy from the same CBCT scan, a threefold increase as compared with 0.7 cGy received during IMRT. With the same kVp, full-fan mode deposited much less dose to organs than half-fan mode, ranging from 9% less for prostate to 69% less for testes, except for rectum, where full-fan mode delivered 34% more dose. As photon beam energy increased from 60 to 125 kV, kVCBCT-contributed doses increased exponentially for all organs, irrespective of scanning mode. Reducing CBCT field span from 30 to 10 cm in the superior-inferior direction cut testicular doses from 5.7 to 0.2 cGy in half-fan mode and from 1.5 to 0.1 cGy in full-fan mode.
  
  
  CONCLUSIONS
  Compared with IMRT, kVCBCT-contributed doses to the prostate, rectum, bladder, and femoral heads are clinically insignificant, whereas dose to the testes is threefold more. Full-fan CBCT usually deposits much less dose to organs (except for rectum) than half-fan mode in prostate patients. Kilovoltage CBCT-contributed doses increase exponentially with photon beam energy. Reducing CBCT field significantly cuts doses to testes and other organs.
authors.affiliation: Department of Therapeutic Radiology, Yale University, New Haven, CT 06510-3221, 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: James B
authors.initials: JB
authors.lastname: Yu
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Roberts
authors.forename: Richard E
authors.initials: RE
authors.lastname: Peschel
authors.forename: Ravinder
authors.initials: R
authors.lastname: Nath
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000009:adverse effects* / Q000379:methods; D019583:Dose Fractionation, Radiation; D005270:Femur Head / Q000000981:diagnostic imaging / Q000528:radiation effects; D006801:Humans; D008297:Male; D009010:Monte Carlo Method; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D019047:Phantoms, Imaging; D011467:Prostate / Q000000981:diagnostic imaging / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000009:adverse effects* / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects* / Q000379:methods; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects; D013737:Testis / Q000000981:diagnostic imaging / Q000528:radiation effects*; D001743:Urinary Bladder / Q000000981:diagnostic imaging / Q000528:radiation effects