Radiation necrosis in the upper cervical spinal cord in a patient treated with proton therapy after radical resection of the fourth ventricle ependymoma
Abstract
Background. Radiation necrosis in eloquent areas of the central nervous system (CNS) is one of the most serious forms of toxicity from radiation therapy.
The occurrence of radiation necrosis in the CNS is described for the period from 3 months to 13 years after radiation therapy. The incidence of this complication covers a wide range from 3 - 47%.
The potential advantage of proton therapy is the ability to reduce dose to normal tissue and escalate tumor dose. Proton beams enter and pass through the tissue with minimal dose deposition until they reach the end of their paths, where the peak of dose, known as the Bragg peak, occurs.
Thereafter, a steep dose fall-off is evident. Such a precisely-distributed dose should reduce the toxicity of the treatment.
Patient. A 23 year-old female patient underwent radical microsurgical resection of anaplastic ependymoma that was originating from the floor of the fourth ventricle.
The tumor was growing into the foramen magnum dorsally from the medulla oblongata. Taking into account the age of the patient, the localization of the tumor and the required dose of 60 Gy, proton therapy was chosen due to the lower risk of damage to the brain stem.
Radiation therapy was performed using pencil beam scanning and one dorsal field. Following this course of treatment radiation necrosis of the medulla oblongata and the upper cervical spinal cord occurred with fatal clinical impact on the patient.
The article analyses possible causes of this complication and there is also a review of the literature. Conclusion.
Despite the theoretical advantages of proton therapy, no clinical benefit in CNS tumors has yet been proved in comparison with modern methods of photon therapy. Proton therapy is accompanied by many uncertainties which can cause unpredictable complications such as radiation necrosis at the edges of the target volume.