Fractionated regimens for stereotactic radiotherapy of recurrent tumors in the brain.

Radiosurgery (single-fraction stereotactic radiotherapy) was initially developed to treat non-malignant arteriovenous malformations, but there is growing interest in its use for the treatment of recurrent brain tumors. We suggest that there are sound reasons to expect improved results for tumor radiotherapy, in terms of late effects, if a fractionated regimen is used. At present, no published guidelines are available for choosing appropriate doses for fractionated regimens. We present two sets of guidelines, based on experimentally derived radiobiological parameters: first, we estimate gamma-ray doses which, if delivered in various numbers of fractions, should produce equivalent early effects to 70 Gy of 125I X rays delivered at low dose rate; this latter regimen is currently used in RTOG interstitial brachytherapy trials. Second, we estimate doses for multi-fractioned stereotactic radiotherapy which may be advantageous alternatives to particular doses of single-fractioned radiosurgical therapy. As the appropriate hardware is available, the use of fractionated stereotactic radiotherapy deserves serious consideration for the treatment of recurrent tumors in the brain.