Skull base and CNS glial tumors

Abstract

INTRODUCTION

• Image-guided radiotherapy started to be utilized over the last decade initially as forward-planned three-dimensional conformal radiation therapy (3DCRT) and later evolved toward inverse-planned delivery of intensity modulated radiation therapy (IMRT) and volumetric arc radiation therapy (VMAT). Stereotactic radiosurgery (SRS), fractionated stereotactic radiotherapy (FSRT), and proton-beam therapy also critically rely on image guidance for target and critical structure delineation.

• Radiotherapy of skull base and posterior fossa tumors is challenging because of the close proximity of the tumors to radiosensitive structures such as lens, eyes, optic pathways, auditory apparatus, and brain stem. These critical structures also play a role in treatment planning of glial tumors which could arise from any lobe of the brain.

• The limiting factor in dose delivery is the tolerance of normal tissue to radiation; the goal is to give the appropriate dose necessary to control the tumor while preserving the surrounding normal tissues within their respective tolerance doses.

• Owing to the variety of tumors affecting the skull base (Table 3-1), a unified classification system has not been established. Therefore, general classifications are being based on either the location or the biologic behavior of the tumor.

• We review the complex anatomy of the skull base to serve as a guide for delineating target and normal tissue, as well as offering several examples.