Stereotactic radiosurgery. VI. Posterior displacement of the brainstem facilitates safer high dose radiosurgery for clival chordoma.

The current 'best treatment method' for clival chordoma is regarded as radical surgical resection followed by radiation therapy; radiosurgery usually plays a major part in the radiation therapy programme. From primate radiation biology studies and from clinical observations, the brainstem is known to be the most radiosensitive part of the central nervous system. The tolerance of the brainstem to high single radiosurgical doses of radiation is limited (all the more so in programmes such as our own where conventionally fractionated radiotherapy precedes radiosurgery or the patient has relapsed after conventional radiotherapy--as in the patient reported here). In this report we describe the operative displacement of the brainstem posteriorly at time of resection such that the proportion of the prescribed postoperative radiosurgical dose received by the brainstem is greatly reduced (by the order of 50%). The gains perceived to accrue from this technique are quantified from isodosimetric considerations not only in dose sparing to the brainstem, but importantly in that the dose to the clival chordoma may be highly significantly increased without exceeding current accepted tolerance brainstem dose limits. Two patients have received this joint surgical/radiosurgical approach to date; the second case is presented here in detail.