title: Radiobiological risk estimates of adverse events and secondary cancer for proton and photon radiation therapy of pediatric medulloblastoma.
abstract: BACKGROUND
  The aim of this model study was to estimate and compare the risk of radiation-induced adverse late effects in pediatric patients with medulloblastoma (MB) treated with either three-dimensional conformal radiotherapy (3D CRT), inversely-optimized arc therapy (RapidArc(®) (RA)) or spot-scanned intensity-modulated proton therapy (IMPT). The aim was also to find dose-volume toxicity parameters relevant to children undergoing RT to be used in the inverse planning of RA and IMPT, and to use in the risk estimations.
  
  
  METHODS
  Treatment plans were created for all three techniques on 10 pediatric patients that have been treated with craniospinal irradiation (CSI) at our institution in 2007-2009. Plans were generated for two prescription CSI doses, 23.4 Gy and 36 Gy. Risk estimates were based on childhood cancer survivor data when available and secondary cancer (SC) risks were estimated as a function of age at exposure and attained age according to the organ-equivalent dose (OED) concept.
  
  
  RESULTS
  Estimates of SC risk was higher for the RA plans and differentiable from the estimates for 3D CRT at attained ages above 40 years. The risk of developing heart failure, hearing loss, hypothyroidism and xerostomia was highest for the 3D CRT plans. The risks of all adverse effects were estimated as lowest for the IMPT plans, even when including secondary neutron (SN) irradiation with high values of the neutron radiation weighting factors (WR(neutron)).
  
  
  CONCLUSIONS
  When comparing RA and 3D CRT treatment for pediatric MB it is a matter of comparing higher SC risk against higher risks of non-cancer adverse events. Considering time until onset of the different complications is necessary to fully assess patient benefit in such a comparison. The IMPT plans, including SN dose contribution, compared favorably to the photon techniques in terms of all radiobiological risk estimates.
authors.affiliation: Radiation Medicine Research Center, Department of Radiation Oncology, Rigshospitalet, University of Copenhagen, Denmark. brodin.patrik@gmail.com
authors.forename: N Patrik
authors.initials: NP
authors.lastname: Brodin
authors.forename: Per
authors.initials: P
authors.lastname: Munck Af Rosenschöld
authors.forename: Marianne C
authors.initials: MC
authors.lastname: Aznar
authors.forename: Anne
authors.initials: A
authors.lastname: Kiil-Berthelsen
authors.forename: Ivan R
authors.initials: IR
authors.lastname: Vogelius
authors.forename: Per
authors.initials: P
authors.lastname: Nilsson
authors.forename: Birgitta
authors.initials: B
authors.lastname: Lannering
authors.forename: Thomas
authors.initials: T
authors.lastname: Björk-Eriksson
mesh_terms: D002528:Cerebellar Neoplasms / Q000532:radiotherapy*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D008527:Medulloblastoma / Q000532:radiotherapy*; D015233:Models, Statistical; D016609:Neoplasms, Second Primary / Q000209:etiology*; D058958:Organs at Risk; D017785:Photons / Q000009:adverse effects*; D011522:Protons / Q000009:adverse effects*; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal; D050397:Radiotherapy, Intensity-Modulated; D018570:Risk Assessment; D016896:Treatment Outcome
chemical_list: D011522:Protons