Stereotactic radiotherapy: a technique for dose optimization and escalation for intracranial tumors

Stereotactic radiosurgery offers the ability to treat relatively small volume intracranial lesions with single fraction, high dose radiotherapy while sparing surrounding tissue due to rapid fall off of dose outside of the treatment volume. Conventional radiotherapy takes advantage of the sparing effects of dose fractionation, but includes relatively large amounts of normal brain in the treatment volume the tolerance of which is dose-limiting. For some intracranial lesions it may not be optimal to treat with large single fractions due to tumor location or size. Conventional fractionated radiotherapy may not be optimum in all cases due to the necessary inclusion of normal structures. Through the development of relocatable head frames, the precision of stereotactic techniques and the biologic advantages of fractionation may be combined in stereotactic radiotherapy (SRT). We report on the treatment of 68 patients with intracranial lesions using a dedicated stereotactic linear accelerator to deliver SRT between June 1992 and June 1993. SRT was used either in order to optimize dose distribution and spare normal tissues in patients with excellent prognosis or in order to increase the dose to tumor while keeping doses to normal tissues below tolerance levels in patients with poorer prognosis (dose escalation). Histologies treated included meningioma, low grade astrocytoma, pituitary adenoma and acoustic neuroma. The most common treatment sites were the parasellar region and cavernous sinuses. Most patients (79%) had surgical debulking prior to SRT. 10-12 patients were treated daily. Patient positioning using relocatable stereotactic frames was highly precise. Acute and subacute side effects were minimal and radiographic responses have been similar to those expected with conventional radiotherapy.(ABSTRACT TRUNCATED AT 250 WORDS)