title: The effect of photon energy on intensity-modulated radiation therapy (IMRT) plans for prostate cancer.
abstract: OBJECTIVE
  To evaluate the effect of common three photon energies (6-MV, 10-MV, and 15-MV) on intensity-modulated radiation therapy (IMRT) plans to treat prostate cancer patients.
  
  
  METHODS
  Twenty patients with prostate cancer treated locally to 81.0 Gy were retrospectively studied. 6-MV, 10-MV, and 15-MV IMRT plans for each patient were generated using suitable planning objectives, dose constraints, and 8-field setting. The plans were analyzed in terms of dose-volume histogram for the target coverage, dose conformity, organs at risk (OAR) sparing, and normal tissue integral dose.
  
  
  RESULTS
  Regardless of the energies chosen at the plans, the target coverage, conformity, and homogeneity of the plans were similar. However, there was a significant dose increase in rectal wall and femoral heads for 6-MV compared to those for 10-MV and 15-MV. The V(20 Gy) of rectal wall with 6-MV, 10-MV, and 15-MV were 95.6%, 88.4%, and 89.4% while the mean dose to femoral heads were 31.7, 25.9, and 26.3 Gy, respectively. Integral doses to the normal tissues in higher energy (10-MV and 15-MV) plans were reduced by about 7%. Overall, integral doses in mid and low dose regions in 6-MV plans were increased by up to 13%.
  
  
  CONCLUSIONS
  In this study, 10-MV prostate IMRT plans showed better OAR sparing and less integral doses than the 6-MV. The biological and clinical significance of this finding remains to be determined afterward, considering neutron dose contribution.
authors.affiliation: Interdisciplinary Program in Radiation Applied Life Science, Seoul National University College of Medicine, Seoul, Korea. ; Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea.
authors.forename: Wonmo
authors.initials: W
authors.lastname: Sung
authors.forename: Jong Min
authors.initials: JM
authors.lastname: Park
authors.forename: Chang Heon
authors.initials: CH
authors.lastname: Choi
authors.forename: Sung Whan
authors.initials: SW
authors.lastname: Ha
authors.forename: Sung-Joon
authors.initials: SJ
authors.lastname: Ye
keywords: Integral dose; Intensity-modulated radiation therapy; Photon energy; Prostate cancer; Treatment planning