Long-term Results after Radiosurgery for Benign Intracranial Tumors

To the Editor:

It was a great pleasure to read the report by Kondziolka et al. (4). A significant number of the patients reported in this series had tumors at locations such as the cavernous sinus. The report offers some evidence that in those patients followed up, excellent rates of tumor control can be achieved across at least schwannomas and meningiomas, which accounted for 85% of the cases in this series. For patients with meningiomas in locations such as the cavernous sinus, this can be welcome news, especially when microneurosurgical resection is judged by the treating team to not be in the patient's best interest (2). However, before we can really appreciate the value of this research, more information is needed on follow-up and on the pretreatment characteristics of patients.

It is well known that the clinical research performed at many tertiary or quaternary care centers, particularly with large numbers of referrals, is often subject to loss of follow-up, and consequently, selection bias can occur. In the present study, as in many other similar studies, it is entirely possible that improved follow-up occurred among patients who had better tumor control and in those who did not develop latent neoplasms. That is, cases of poor outcome were lost to follow-up. Thus, one has to interpret the excellent rates of 10-year actuarial control cautiously, because when large numbers of patients are lost to follow-up, the validity of such estimates can become suspect.

In this study, although it seems that all patients were treated for more than 10 years, in fact, only 45% of patients seem to have had follow-up to or beyond the 10-year period. One needs to know the status of the other 55% of patients who did not reach 10-year follow-up to make a more valid assessment of the long-term value of radiosurgery. With the exception of the vestibular schwannoma group, the number of individuals available for follow-up at 5, 10, and 15 years was not provided in sufficient detail to allow readers to simulate the degree of precision that was achieved in this study. In the vestibular schwannoma group, 54 of 157 patients treated before 1992 were followed up for more than 10 years. If the group of patients lost to attrition had 10-year control rates similar to those reported by Goldsmith et al. (3) (or even lower), the control rate for the whole group with radiosurgery could be substantially lower than that reported. Alternatively, the control rate could conceivably be higher if control rates in the patients not accounted for were better than in those patients who actually received complete follow-up in the report. Similarly, if just two patients among those lost to follow-up developed radiation-associated malignant tumors, the rate of malignant transformation would not be unlike that of large-field radiotherapy (1).

In addition to the issue of follow-up, it must also be realized that before we can say that radiosurgery provided a high rate of tumor growth “cessation” (as the authors state, p. 819), we need to know exactly how many of these tumors had actually been growing before radiosurgery. It is well known that a significant proportion of meningiomas are diagnosed incidentally and that many others are discovered with minimal symptoms and are probably growing at slow rates. Obviously, studies reporting on patients with a high proportion of these types of slowly growing or nongrowing tumors would report excellent tumor control rates, when in fact treatment results may not be that much better than observation alone (but with added risk). Understanding the preradiosurgery growth rates of the tumors that were not controlled and comparing these rates with preradiosurgery growth rates for those cases that were controlled would be an important advancement toward understanding the long-term value of radiosurgery.

1.

Breen P, Flickinger JC, Kondziolka D, Martinez AJ: Radiotherapy for non-functional pituitary adenoma: Analysis of long-term tumor control. J Neurosurg 89:933–938, 1998.

2.

Cusimano MD, Sekhar LN, Sen C, Pomonis S, Biglan A, Jannetta PJ: Results of surgery for benign tumors of the cavernous sinus. Neurosurgery 42:1–12, 1995.

3.

Goldsmith BJ, Wara WM, Wilson CB, Larson DA: Postoperative iRadiation for subtotally resected meningiomas: A retrospective analysis of 140 patients treated from 1967 to 1990. J Neurosurg 80:195–201, 1994.

4.

Kondziolka D, Nathoo N, Flickinger JC, Niranjan A, Maitz AH, Lunsford LD: Long-term results after radiosurgery for benign intracranial tumors. Neurosurgery 53:815–823, 2003.