title: Partial kilovoltage cone beam computed tomography, complete kilovoltage cone beam computed tomography, and electronic portal images for breast radiation therapy: A dose-comparison study.
abstract: OBJECTIVE
  The purpose of this study was to compare absorbed dose with the treated breast and organs at risks (OARs) with weekly image guidance using electronic portal imaging (EPI), complete kilovoltage cone beam computed tomography (kV CBCT), and partial kV CBCT.
  
  
  METHODS
  Using a thorax female phantom, we determined absorbed doses to treated and contralateral breast, ipsilateral and contralateral lung, heart, and skin for tangential EPI, complete kV CBCT, and partial kV CBCT. Doses were measured by use of ionization chambers and compared with treatment planning system calculations. With simulation of breast tangential irradiation to a standard dose of 50 Gy in 25 fractions, dose to each organ was measured for each image guidance technique.
  
  
  RESULTS
  Use of weekly EPI was associated with a significantly increased dose to the treated breast compared with weekly complete and partial kV CBCT (4.44 ± 0.04 vs 1.00 ± 0.07 vs 0.576 ± 0.003 cGy, respectively). Dose to the contralateral breast, ipsilateral and contralateral lung, heart, and contralateral skin was lower with EPI than with either complete or partial kV CBCT (0.042 ± 0.004 vs 0.36 ± 0.01 vs 0.23 ± 0.01 cGy, 0.06 ± 0.04 vs 0.42 ± 0.02 vs 0.31 ± 0.01 cGy, 0.004 ± 0.002 vs 0.29 ± 0.01 vs 0.22 ± 0.01 cGy, 0.03 ± 0.08 vs 0.36 ± 0.02 vs 0.25 ± 0.01 cGy, and 0.20 ± 0.02 vs 0.80 ± 0.06 vs 0.40 ± 0.03 cGy, respectively). Compared with complete CBCT, the use of partial CBCT allowed dose reductions of 42%, 37%, 27%, 24%, and 28% to the ipsilateral breast, contralateral breast, ipsilateral lung, contralateral lung, and heart, respectively. Additional dose from weekly CBCT was significantly lower than treatment-related scatter dose for all OARs.
  
  
  CONCLUSIONS
  Use of CBCT was associated with decreased dose to ipsilateral breast and increased dose to all OARs compared with EPI. Significant dose reduction can be achieved with the use of partial CBCT, while generally maintaining image quality.
authors.affiliation: Radiation Oncology Department, Maisonneuve-Rosemont Hospital, Montréal, Quebec, Canada.
authors.forename: Houda
authors.initials: H
authors.lastname: Bahig
authors.affiliation: Radiation Oncology Department, Maisonneuve-Rosemont Hospital, Montréal, Quebec, Canada.
authors.forename: Étienne
authors.initials: É
authors.lastname: Roussin
authors.affiliation: Radiation Oncology Department, Maisonneuve-Rosemont Hospital, Montréal, Quebec, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Yassa
authors.affiliation: Radiation Oncology Department, Maisonneuve-Rosemont Hospital, Montréal, Quebec, Canada.
authors.forename: Peter
authors.initials: P
authors.lastname: Vavassis
authors.affiliation: Radiation Oncology Department, Maisonneuve-Rosemont Hospital, Montréal, Quebec, Canada.
authors.forename: Céline
authors.initials: C
authors.lastname: Lemaire
authors.affiliation: Radiation Oncology Department, Maisonneuve-Rosemont Hospital, Montréal, Quebec, Canada.
authors.forename: Laurie
authors.initials: L
authors.lastname: Archambault
authors.affiliation: Radiation Oncology Department, Maisonneuve-Rosemont Hospital, Montréal, Quebec, Canada. Electronic address: dnguyen.hmr@ssss.gouv.qc.ca.
authors.forename: David H A
authors.initials: DHA
authors.lastname: Nguyen
mesh_terms: D001943:Breast Neoplasms / Q000532:radiotherapy; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005260:Female; D006801:Humans; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*