Advantage of protons compared to conventional X-ray or IMRT in the treatment of a pediatric patient with medulloblastoma.

Purpose: To compare treatment plans from standard photon therapy to intensity modulated X-rays (IMRT) and protons for craniospinal axis irradiation and posterior fossa boost in a patient with medulloblastoma.
Methods: Proton planning was accomplished using an in-house 3D planning system. IMRT plans were developed using the KonRad treatment planning system with 6-MV photons.
Results: Substantial normal-tissue dose sparing was realized with IMRT and proton treatment of the posterior fossa and spinal column. For example, the dose to 90% of the cochlea was reduced from 101.2% of the prescribed posterior fossa boost dose from conventional X-rays to 33.4% and 2.4% from IMRT and protons, respectively. Dose to 50% of the heart volume was reduced from 72.2% for conventional X-rays to 29.5% for IMRT and 0.5% for protons. Long-term toxicity with emphasis on hearing and endocrine and cardiac function should be substantially improved secondary to nontarget tissue sparing achieved with protons.
Conclusion: The present study clearly demonstrates the advantage of conformal radiation methods for the treatment of posterior fossa and spinal column in children with medulloblastoma, when compared to conventional X-rays. Of the two conformal treatment methods evaluated, protons were found to be superior to IMRT.