title: Comparative study of the calculated risk of radiation-induced cancer after photon- and proton-beam based radiosurgery of liver metastases.
abstract: BACKGROUND
  The potential of proton therapy to improve the sparing of the healthy tissue has been demonstrated in several studies. However, even small doses delivered to the organs at risk (OAR) may induce long-term detriments after radiotherapy. In this study, we investigated the possibility to reduce the risk of radiation-induced secondary cancers with intensity modulated proton therapy (IMPT), when used for radiosurgery of liver metastases.
  
  
  METHODS
  Ten patients, previously treated for liver metastases with photon-beam based stereotactic body radiation therapy (SBRT) were retrospectively planned for radiosurgery with IMPT. A treatment plan comparison was then performed in terms of calculated risk of radiation-induced secondary cancer. The risks were estimated using two distinct models (Dasu et al., 2005; Schneider et al., 2005, 2009). The plans were compared pairwise with a two-sided Wilcoxon signed-rank test with a significance level of 0.05.
  
  
  RESULTS
  Reduced risks for induction of fatal and other types of cancers were estimated for the IMPT plans (p<0.05) with the Dasu et al.
  
  
  METHODS
  Using the Schneider et al. model, lower risks for carcinoma-induction with IMPT were estimated for the skin, lungs, healthy part of the liver, esophagus and the remaining part of the body (p<0.05). The risk of observing sarcomas in the bone was also reduced with IMPT (p<0.05).
  
  
  CONCLUSIONS
  The findings of this study indicate that the risks of radiation-induced secondary cancers after radiosurgery of liver metastases may be reduced, if IMPT is used instead of photon-beam based SBRT.
authors.affiliation: Department of Physics - Medical Radiation Physics, Stockholm University, Stockholm, Sweden; Department of Physics, Universidade Eduardo Mondlane, Maputo, Mozambique. Electronic address: gracinda.mondlane@fysik.su.se.
authors.forename: Gracinda
authors.initials: G
authors.lastname: Mondlane
authors.affiliation: Department of Oncology and Pathology, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Michael
authors.initials: M
authors.lastname: Gubanski
authors.affiliation: Department of Oncology and Pathology, Karolinska University Hospital, Stockholm, Sweden; Department of Oncology, Södersjukhuset, Stockholm, Sweden.
authors.forename: Pehr A
authors.initials: PA
authors.lastname: Lind
authors.affiliation: Department of Physics - Medical Radiation Physics, Stockholm University, Stockholm, Sweden.
authors.forename: Ana
authors.initials: A
authors.lastname: Ureba
authors.affiliation: Department of Physics - Medical Radiation Physics, Stockholm University, Stockholm, Sweden.
authors.forename: Albert
authors.initials: A
authors.lastname: Siegbahn
mesh_terms: D000368:Aged; D002277:Carcinoma / Q000453:epidemiology / Q000209:etiology; D006801:Humans; D008113:Liver Neoplasms / Q000453:epidemiology / Q000532:radiotherapy* / Q000556:secondary*; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology*; D017785:Photons / Q000627:therapeutic use*; D061766:Proton Therapy / Q000009:adverse effects*; D016634:Radiosurgery / Q000009:adverse effects*; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects; D012189:Retrospective Studies
keywords: IMPT; Liver metastases; SBRT; Secondary cancers