A treatment planning comparison of combined photon-proton beams versus proton beams-only for the treatment of skull base tumors.
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.
Feuvret
Loïc
L
Institut Curie, Centre de Protonthérapie d'Orsay, Orsay Cedex, France. loic.feuvret@psl.aphp.fr
Noel
Georges
G
Weber
Damien C
DC
Pommier
Pascal
P
Ferrand
Regis
R
De Marzi
Ludovic
L
Dhermain
Frederic
F
Alapetite
Claire
C
Mammar
Hamid
H
Boisserie
Gilbert
G
Habrand
Jean-Louis
JL
Mazeron
Jean-Jacques
JJ
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
D011522:Protons