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Children treated for brain tumors often have significant long-term effects from the radiation therapy. Even low doses can produce declines in memory and intelligence, as well as damage to the hypothalamus and pituitary gland, which produce or direct the production of essential hormones such as growth hormone, thyroid hormone, cortisone, as well as reproductive and sexual hormones. Moderate doses, especially in combination with some chemotherapy drugs such as cis-platinum, can cause hearing loss and other complications. High doses can occasionally cause very dramatic deficits such as paralysis or loss of vision. In comparison with conventional photon therapy, proton radiation spares more normal tissue, reducing the risk of all these complications.
As noted earlier, proton therapy may lower the risk of secondary cancers from the radiation. Early data from proton therapy indicates that the risk is lower than with conventional therapy.
Ependymomas are tumors that originate in or near the ventricles of the brain, which are cavities that contain cerebrospinal fluid (CSF). Ependymomas arise from the cells lining the ventricles, often in the 4th ventricle. The most important treatment for an ependymoma is careful surgical removal, but radiation therapy is usually required after surgery to reduce the risk of recurrence. Proton therapy is ideal for ependymomas of the 4th ventricle, whether or not the tumor can be surgically resected. Proton therapy eliminates radiation to the hormone and intellectual centers of the brain, as well as the middle ear, which occurs with even the most sophisticated conventional radiation therapy techniques. Information available at the present time indicates that avoiding even low doses to these important areas of the brain will reduce treatment effects on the child’s intelligence, memory, hearing, and hormone production. Ependymomas of other regions of the brain can benefit from proton irradiation as well.
Tumors of the Third Ventricle
There are important structures in the third ventricular area of the brain including the visual apparatus, the pituitary gland, and the hypothalamic gland. Also surrounding the third ventricle the temporal lobes harbor memory and other aspects of intellectual function, making this area particularly susceptible to both surgery and radiation injury. Tumors of this area include craniopharyngioma and optic pathway tumors. Craniopharyngiomas are not malignant, but can cause death by pressure on the brain. They originate just above the base of the skull and below the brain and may grow slowly, usually developing a cystic component (a cavity filled with fluid) and a solid component, which may calcify. Complete removal is frequently not possible without significant brain injury. The best treatment is often drainage of the cyst followed by radiation therapy. Optic pathway tumors can arise in the optic (visual) nerve from each eye, in the chiasm (where the optic nerves from each eye join together), or in the hypothalamic region. The hypothalamus, which is above and behind the pituitary gland, directs the pituitary gland to produce many of the hormones required for normal bodily function. Proton therapy for tumors of the third ventricle region, including craniopharyngiomas and optic pathway tumors, can better spare adjacent tissues than conventional radiation therapy including intellectual and memory centers in midbrain and temporal lobes, which should decrease the long-term intellectual effects of treatment.
This is one of the most common malignancies in children. It usually starts in the 4th ventricle region, similar to many ependymomas. However, it is a high-grade tumor that can use the fluid circulating in the nervous system to spread throughout the brain and spine. Although surgery is needed for diagnosis and symptom relief, the most important part of the treatment for non-infants is radiation therapy, including radiation to the entire brain and spine. This treatment, called craniospinal irradiation (CSI), is usually given within a few weeks after surgery. In addition to the usual risks of treating the central nervous system mentioned above, spinal treatment with conventional radiation gives radiation to the lung, heart, thyroid, bowel, liver and kidneys, and gonads. Proton therapy significantly reduces radiation to the lungs and eliminates any radiation to other organs. After craniospinal axis irradiation, additional radiation is given to the tumor itself or surgical bed in the 4th ventricle. The use of protons for this part of treatment will also decrease the long-term intellectual and hearing effects by eliminating any further radiation to those sites.
Other tumors of the brain and central nervous system
Any tumors receiving CSI as part of the therapy (e.g., germ cell tumors, atypical rhabdoid tumors, and pineal tumors) should benefit from proton treatment for many of the same reasons given in the above section on medulloblastoma. Localized tumors of any type should also benefit by eliminating or decreasing radiation doses to sensitive areas of the brain.
We currently have protocols open for the following pediatric brain tumors:
Other pediatric brain tumors will be evaluated for proton therapy on a case-by-case basis.