title: Radiation-induced cancers from modern radiotherapy techniques: intensity-modulated radiotherapy versus proton therapy.
abstract: OBJECTIVE
  To assess and compare secondary cancer risk resulting from intensity-modulated radiotherapy (IMRT) and proton therapy in patients with prostate and head-and-neck cancer.
  
  
  METHODS
  Intensity-modulated radiotherapy and proton therapy in the scattering mode were planned for 5 prostate cancer patients and 5 head-and-neck cancer patients. The secondary doses during irradiation were measured using ion chamber and CR-39 detectors for IMRT and proton therapy, respectively. Organ-specific radiation-induced cancer risk was estimated by applying organ equivalent dose to dose distributions.
  
  
  RESULTS
  The average secondary doses of proton therapy for prostate cancer patients, measured 20-60 cm from the isocenter, ranged from 0.4 mSv/Gy to 0.1 mSv/Gy. The average secondary doses of IMRT for prostate patients, however, ranged between 3 mSv/Gy and 1 mSv/Gy, approximately one order of magnitude higher than for proton therapy. Although the average secondary doses of IMRT were higher than those of proton therapy for head-and-neck cancers, these differences were not significant. Organ equivalent dose calculations showed that, for prostate cancer patients, the risk of secondary cancers in out-of-field organs, such as the stomach, lungs, and thyroid, was at least 5 times higher for IMRT than for proton therapy, whereas the difference was lower for head-and-neck cancer patients.
  
  
  CONCLUSIONS
  Comparisons of organ-specific organ equivalent dose showed that the estimated secondary cancer risk using scattering mode in proton therapy is either significantly lower than the cases in IMRT treatment or, at least, does not exceed the risk induced by conventional IMRT treatment.
authors.affiliation: Proton Therapy Center, National Cancer Center, Goyang, Korea. mxy131@ncc.re.kr
authors.forename: Myonggeun
authors.initials: M
authors.lastname: Yoon
authors.forename: Sung Hwan
authors.initials: SH
authors.lastname: Ahn
authors.forename: Jinsung
authors.initials: J
authors.lastname: Kim
authors.forename: Dong Ho
authors.initials: DH
authors.lastname: Shin
authors.forename: Sung Yong
authors.initials: SY
authors.lastname: Park
authors.forename: Se Byeong
authors.initials: SB
authors.lastname: Lee
authors.forename: Kyung Hwan
authors.initials: KH
authors.lastname: Shin
authors.forename: Kwan Ho
authors.initials: KH
authors.lastname: Cho
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000209:etiology*; D009502:Neutrons; D009928:Organ Specificity; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011522:Protons / Q000009:adverse effects*; D011874:Radiometry / Q000295:instrumentation; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*; D018570:Risk Assessment; D012542:Scattering, Radiation
chemical_list: D011522:Protons