title: A treatment planning comparison of combined photon-proton beams versus proton beams-only for the treatment of skull base tumors.
abstract: OBJECTIVE
  To compare treatment planning between combined photon-proton planning (CP) and proton planning (PP) for skull base tumors, so as to assess the potential limitations of CP for these tumors.
  
  
  METHODS
  Plans for 10 patients were computed for both CP and PP. Prescribed dose was 67 cobalt Gray equivalent (CGE) for PP; 45 Gy (photons) and 22 CGE (protons) for CP. Dose-volume histograms (DVHs) were calculated for gross target volume (GTV), clinical target volume (CTV), normal tissues (NT), and organs at risk (OARs) for each plan. Results were analyzed using DVH parameters, inhomogeneity coefficient (IC), and conformity index (CI).
  
  
  RESULTS
  Mean doses delivered to the GTVs and CTVs with CP (65.0 and 61.7 CGE) and PP (65.3 and 62.2 Gy CGE) were not significantly different (p > 0.1 and p = 0.72). However, the dose inhomogeneity was drastically increased with CP, with a mean significant incremental IC value of 10.5% and CP of 6.8%, for both the GTV (p = 0.01) and CTV (p = 0.04), respectively. The CI(80%) values for the GTV and CTV were significantly higher with PP compared with CP. Compared with CP, the use of protons only led to a significant reduction of NT and OAR irradiation, in the intermediate-to-low dose (< or =80% isodose line) range.
  
  
  CONCLUSIONS
  These results suggest that the use of CP results in levels of target dose conformation similar to those with PP. Use of PP significantly reduced the tumor dose inhomogeneity and the delivered intermediate-to-low dose to NT and OARs, leading us to conclude that this treatment is mainly appropriate for tumors in children.
authors: Institut Curie, Centre de Protonthérapie d'Orsay, Orsay Cedex, France. loic.feuvret@psl.aphp.fr
authors: Loïc
authors: L
authors: Feuvret
authors: Georges
authors: G
authors: Noel
authors: Damien C
authors: DC
authors: Weber
authors: Pascal
authors: P
authors: Pommier
authors: Regis
authors: R
authors: Ferrand
authors: Ludovic
authors: L
authors: De Marzi
authors: Frederic
authors: F
authors: Dhermain
authors: Claire
authors: C
authors: Alapetite
authors: Hamid
authors: H
authors: Mammar
authors: Gilbert
authors: G
authors: Boisserie
authors: Jean-Louis
authors: JL
authors: Habrand
authors: Jean-Jacques
authors: JJ
authors: Mazeron
mesh_terms: D000465:Algorithms; D001933:Brain Stem / Q000528:radiation effects; D002813:Chondrosarcoma / Q000473:pathology / Q000532:radiotherapy*; D002817:Chordoma / Q000473:pathology / Q000532:radiotherapy*; D005123:Eye / Q000528:radiation effects; D006801:Humans; D008279:Magnetic Resonance Imaging; D009897:Optic Chiasm / Q000528:radiation effects; D017785:Photons / Q000627:therapeutic use*; D061766:Proton Therapy; D011832:Radiation Injuries / Q000517:prevention & control; D011879:Radiotherapy Dosage / Q000592:standards*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal; D019292:Skull Base Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden; D011522:Protons
chemical_list: D011522:Protons