Stereotactic radiotherapy is useful for the management of residual or recurrent tumor after surgical excision, and it can be used as a primary modality for benign lesions, he said.
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February 2008Skull base meningiomas are usually well circumscribed, and reported tumor control is between 84% and 100% following stereotactic radiotherapy. Treatment failure due to tumor progression often occurs outside the tumor volume. Meningiomas can be successfully treated stereotactically without vision loss, he said. For pituitary adenomas, long-term control rates range from 50% to 80%. A large meta-analysis of more than 1600 patients with pituitary adenomas showed 90% tumor control with use of stereotacic radiosurgery (Sheehan, J Neurosurg 2005). Complications included 16 cases of optic nerve damage, a zero to 36% risk of pituitary dysfunction, and 13 cases of parenchymal brain injury. There were no radiotherapy-induced brain lesions, Dr. Batra said.
Chordomas are rare benign tumors that can be locally aggressive and tend to recur. Two small series reported tumor control rates of 82% at four years and 83% at five years, respectively, he said. A small series of 14 cases of malignant olfactory neuroblastomas treated with endoscopic resection followed by a single dose of stereotactic radiotherapy reported 100% tumor control and survival at five years.
Other malignancies will be the next area of exploration. Skull base lesions remain a challenge and stereotactic radiotherapy will be useful as an adjunct to minimally invasive surgery, Dr. Batra stated.
Acoustic Tumors
In his discussion of acoustic neuromas, Derald Brackmann, MD, of the House Ear Clinic in Los Angeles, addressed three issues: a comparison of stereotactic radiotherapy with microsurgery; stereotactic radiotherapy in combination with microsurgery; and stereotactic radiotherapy treatment failures.
In comparing stereotactic radiotherapy with microsurgery, on the surface the advantages of stereotactic radiotherapy are attractive to patients, and it would seem that most patients would opt for this technique over microsurgery, he said. Stereotactic radiotherapy is an outpatient procedure with less morbidity than surgery, and has potentially better preservation of the facial nerve and hearing.
However, there are several important disadvantages, he continued. These include the lack of a tissue diagnosis, the potential for continued tumor growth, induction of other tumors, and, finally, malignant transformation of the tumor. In addition, stereotactic radiotherapy does not improve pre-existing dizziness.
In contrast, microsurgery has the advantages of providing a tissue diagnosis, tumor removal, and the control of dizziness. However, microsurgery has a longer recovery time and a greater risk of morbidity such as infection and spinal fluid leaks, and a somewhat greater loss of hearing and risk of facial nerve problems, Dr. Brackmann said.