Stereotactic Radiotherapy Treats Skull Base Tumors: Part 2 of

WASHINGTON, DC-Stereotactic radiotherapy is increasingly gaining favor as an attractive alternative to conventional surgery of the skull base and head and neck. A panel of experts at the recent annual meeting of the American Academy of Otolaryngology-Head and Neck Surgery discussed potential uses of stereotactic modalities in otolaryngology practices and agreed that optimal candidates still need to be defined for these procedures, but that this treatment option provides an opportunity for participation and leadership among otolaryngologists.

Tumors amenable to stereotactic radiotherapy (other than acoustic neuroma) include paraganglioma (most common), schwannoma, meningioma, malignant tumors in the posterior fossa, pituitary tumors, and rarer tumors such as craniopharyngioma, chondroblastoma, and chordosarcoma, said Stephen P. Cass, MD, Associate Professor of Otolaryngology at the University of Colorado Health Sciences Center in Denver.

Factors to consider when deciding between surgery and stereotactic radiotherapy include age of patient (the younger the patient, the higher the risk of regrowth and secondary radiation-induced tumors), operability of lesions, likelihood of at least near total resection, likelihood of cranial nerve or vascular morbidity, and primary versus recurrent tumor. Dr. Cass noted that surgery was the preferred option if the tumor is resectable with minimal morbidity, and he said that stereotactic radiotherapy is preferred for recurrent tumors.

He cautioned that watchful waiting should always be considered, especially for elderly patients. Also, it is important to assess whether the patient has a tumor-prone condition. Stereotactic radiotherapy should only be used if the lesion is well defined and if the adjacent structures can tolerate radiation exposure, he added.

In a series of 10 patients with paragangliomas treated with stereotactic radiotherapy at the University of Colorado, tumor control was 100% at 3- to 4.5-year follow-up. These were relatively large tumors, with a mean of 7.3 cm, he said. Three out of four patients with pulsatile tinnitus had resolution of this annoying symptom. Also, he has successfully treated five schwannomas of cranial nerves 7, 10, and 12.

In summary, Dr. Cass said that stereotactic radiotherapy is a reasonable option for various skull base tumors. The risk of acute toxicity is low, and short-term tumor control is excellent. Late complications can occur, he noted, but are rare.

Anterior Skull Base Tumors

Stereotactic radiotherapy is a valuable adjunct to minimally invasive surgery for anterior skull base tumors, which are difficult to access, said Pete S. Batra, MD, Assistant Professor of Surgery at the Cleveland Clinic Head and Neck Institute.

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.

Skull 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.

Stereotactic radiotherapy has additional limitations, continued Dr. Brackmann. Long-term tumor control rates are unknown. Many non-growing tumors have been treated, a practice that he condemns. If only growing tumors are treated, the control rate is likely to be less. Over the short term, 5% to 10% of tumors continue growing and require surgical removal. Complications of surgery are increased following stereotactic radiation.

Physicians at the House Ear Clinic have now had experience with 62 stereotactic radiotherapy failures. There is an increased risk to the facial nerve in surgery following failed radiotherapy. In nonirradiated tumors, there is a 98.6% anatomic preservation of the facial nerve. This falls to 82% when the surgery is necessary following irradiation failure, Dr. Brackmann noted.

Microsurgery may be used in combination with stereotactic radiotherapy, Dr. Brackmann continued; he suggested subtotal removal with microsurgery followed by stereotactic radiotherapy for tumors greater than 3 cm. At the House Clinic, total removal is planned but subtotal resection is performed if the facial nerve is at risk. This happens in about 5% of cases, he said.

The complication rate of stereotactic radiotherapy is still unknown in that complications may occur 20 to 40 years after radiotherapy, and low-dose radiation is more likely to induce tumors than high-dose radiation. There is an eightfold increase in benign intracranial tumors after low-dose radiation for tinea capitis. There is a 1,000-fold increase in acoustic neuromas after radiation for tonsils and adenoids. To date, there have been 20 reported cases of malignant induction or transformation, all fatal. These cases of malignant transformation may be just the tip of the iceberg, and you need to discuss these risks with patients, he said.

Dr. Brackmann concluded that microsurgery remains the established treatment of choice, particularly in younger patients. Stereotactic radiotherapy is a reasonable alternative, particularly in older patients, but the final place of this treatment is still being defined.

©2008 The Triological Society