title: Predicted risks of radiogenic cardiac toxicity in two pediatric patients undergoing photon or proton radiotherapy.
abstract: BACKGROUND
  Hodgkin disease (HD) and medulloblastoma (MB) are common malignancies found in children and young adults, and radiotherapy is part of the standard treatment. It was reported that these patients who received radiation therapy have an increased risk of cardiovascular late effects. We compared the predicted risk of developing radiogenic cardiac toxicity after photon versus proton radiotherapies for a pediatric patient with HD and a pediatric patient with MB.
  
  
  METHODS
  In the treatment plans, each patient's heart was contoured in fine detail, including substructures of the pericardium and myocardium. Risk calculations took into account both therapeutic and stray radiation doses. We calculated the relative risk (RR) of cardiac toxicity using a linear risk model and the normal tissue complication probability (NTCP) values using relative seriality and Lyman models. Uncertainty analyses were also performed.
  
  
  RESULTS
  The RR values of cardiac toxicity for the HD patient were 7.27 (proton) and 8.37 (photon), respectively; the RR values for the MB patient were 1.28 (proton) and 8.39 (photon), respectively. The predicted NTCP values for the HD patient were 2.17% (proton) and 2.67% (photon) for the myocardium, and were 2.11% (proton) and 1.92% (photon) for the whole heart. The predicted ratios of NTCP values (proton/photon) for the MB patient were much less than unity. Uncertainty analyses revealed that the predicted ratio of risk between proton and photon therapies was sensitive to uncertainties in the NTCP model parameters and the mean radiation weighting factor for neutrons, but was not sensitive to heart structure contours. The qualitative findings of the study were not sensitive to uncertainties in these factors.
  
  
  CONCLUSIONS
  We conclude that proton and photon radiotherapies confer similar predicted risks of cardiac toxicity for the HD patient in this study, and that proton therapy reduced the predicted risk for the MB patient in this study.
authors.affiliation: The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX, USA. rzhang@marybird.com
authors.forename: Rui
authors.initials: R
authors.lastname: Zhang
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Howell
authors.forename: Kenneth
authors.initials: K
authors.lastname: Homann
authors.forename: Annelise
authors.initials: A
authors.lastname: Giebeler
authors.forename: Phillip J
authors.initials: PJ
authors.lastname: Taddei
authors.forename: Anita
authors.initials: A
authors.lastname: Mahajan
authors.forename: Wayne D
authors.initials: WD
authors.lastname: Newhauser
mesh_terms: D002648:Child; D002675:Child, Preschool; D005260:Female; D006321:Heart / Q000528:radiation effects*; D006689:Hodgkin Disease / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008482:Mediastinum / Q000528:radiation effects; D008527:Medulloblastoma / Q000532:radiotherapy*; D009206:Myocardium / Q000473:pathology; D009502:Neutrons; D010496:Pericardium / Q000473:pathology; D017785:Photons; D011336:Probability; D011522:Protons / Q000009:adverse effects; D011832:Radiation Injuries / Q000517:prevention & control; D011878:Radiotherapy / Q000009:adverse effects*; D011880:Radiotherapy Planning, Computer-Assisted; D012306:Risk; D014057:Tomography, X-Ray Computed
chemical_list: D011522:Protons