title: Secondary radiation doses of intensity-modulated radiotherapy and proton beam therapy in patients with lung and liver cancer.
abstract: OBJECTIVE
  To compare the secondary radiation doses following intensity-modulated radiotherapy (IMRT) and proton beam therapy (PBT) in patients with lung and liver cancer.
  
  
  METHODS
  IMRT and PBT were planned for three lung cancer and three liver cancer patients. The treatment beams were delivered to phantoms and the corresponding secondary doses during irradiation were measured at various points 20-50 cm from the beam isocenter using ion chamber and CR-39 detectors for IMRT and PBT, respectively.
  
  
  RESULTS
  The secondary dose per Gy (i.e., a treatment dose of 1Gy) from PBT for lung and liver cancer, measured 20-50 cm from the isocenter, ranged from 0.17 to 0.086 mGy. The secondary dose per Gy from IMRT, however, ranged between 5.8 and 1.0 mGy, indicating that PBT is associated with a smaller dose of secondary radiation than IMRT. The internal neutron dose per Gy from PBT for lung and liver cancer, 20-50 cm from the isocenter, ranged from 0.03 to 0.008 mGy.
  
  
  CONCLUSIONS
  The secondary dose from PBT is less than or compatible to the secondary dose from conventional IMRT. The internal neutron dose generated by the interaction between protons and body material is generally much less than the external neutron dose from the treatment head.
authors.affiliation: Proton Therapy Center, National Cancer Center, Goyang, Republic of Korea.
authors.forename: Seonkyu
authors.initials: S
authors.lastname: Kim
authors.forename: Byung Jun
authors.initials: BJ
authors.lastname: Min
authors.forename: Myonggeun
authors.initials: M
authors.lastname: Yoon
authors.forename: Jinsung
authors.initials: J
authors.lastname: Kim
authors.forename: Dong Ho
authors.initials: DH
authors.lastname: Shin
authors.forename: Se Byeong
authors.initials: SB
authors.lastname: Lee
authors.forename: Sung Yong
authors.initials: SY
authors.lastname: Park
authors.forename: Sungkoo
authors.initials: S
authors.lastname: Cho
authors.forename: Dae Hyun
authors.initials: DH
authors.lastname: Kim
mesh_terms: D006801:Humans; D008113:Liver Neoplasms / Q000532:radiotherapy*; D008175:Lung Neoplasms / Q000532:radiotherapy*; D009502:Neutrons; D011522:Protons; D011832:Radiation Injuries; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects
chemical_list: D011522:Protons