For 6 MV x-rays>60% of the dose prescribed to the target was delivered to 44% of the heart volume, while the proton beam was able to completely avoid the heart, the liver, and in all likelihood the thyroid and gonads as well.CONCLUSION: The present study demonstrates a potential role of proton therapy in decreasing the dose (and toxicity) to the critical structures in the irradiation of the spinal neuraxis in medulloblastoma/PNET.