title: On the benefits and risks of proton therapy in pediatric craniopharyngioma.
abstract: OBJECTIVE
  Craniopharyngioma is a pediatric brain tumor whose volume is prone to change during radiation therapy. We compared photon- and proton-based irradiation methods to determine the effect of tumor volume change on target coverage and normal tissue irradiation in these patients.
  
  
  METHODS
  For this retrospective study, we acquired imaging and treatment-planning data from 14 children with craniopharyngioma (mean age, 5.1 years) irradiated with photons (54 Gy) and monitored by weekly magnetic resonance imaging (MRI) examinations during radiation therapy. Photon intensity-modulated radiation therapy (IMRT), double-scatter proton (DSP) therapy, and intensity-modulated proton therapy (IMPT) plans were created for each patient based on his or her pre-irradiation MRI. Target volumes were contoured on each weekly MRI scan for adaptive modeling. The measured differences in conformity index (CI) and normal tissue doses, including functional sub-volumes of the brain, were compared across the planning methods, as was target coverage based on changes in target volumes during treatment.
  
  
  RESULTS
  CI and normal tissue dose values of IMPT plans were significantly better than those of the IMRT and DSP plans (p < 0.01). Although IMRT plans had a higher CI and lower optic nerve doses (p < 0.01) than did DSP plans, DSP plans had lower cochlear, optic chiasm, brain, and scanned body doses (p < 0.01). The mean planning target volume (PTV) at baseline was 54.8 cm(3), and the mean increase in PTV was 11.3% over the course of treatment. The dose to 95% of the PTV was correlated with a change in the PTV; the R(2) values for all models, 0.73 (IMRT), 0.38 (DSP), and 0.62 (IMPT), were significant (p < 0.01).
  
  
  CONCLUSIONS
  Compared with photon IMRT, proton therapy has the potential to significantly reduce whole-brain and -body irradiation in pediatric patients with craniopharyngioma. IMPT is the most conformal method and spares the most normal tissue; however, it is highly sensitive to target volume changes, whereas the DSP method is not.
authors.affiliation: Division of Radiation Oncology, St Jude Children's Research Hospital, Memphis, TN 38105-2794, USA.
authors.forename: Chris
authors.initials: C
authors.lastname: Beltran
authors.forename: Monica
authors.initials: M
authors.lastname: Roca
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Merchant
mesh_terms: D000293:Adolescent; D001921:Brain / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000528:radiation effects; D002648:Child; D002675:Child, Preschool; D003051:Cochlea / Q000528:radiation effects; D003397:Craniopharyngioma / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D009897:Optic Chiasm / Q000528:radiation effects; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D017785:Photons / Q000627:therapeutic use*; D010911:Pituitary Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden / Q000528:radiation effects*; D011522:Protons
chemical_list: D011522:Protons