Stereotactic radiotherapy of intracranial tumors : optimizing treatment and improving outcome

Abstract

This thesis consists of studies on stereotactic radiotherapy (SRT) of intracranial tumors aiming at optimizing the treatment technique and improving the patients__ outcome. We compared two treatment planning techniques (dynamic conformal arc and intensity-modulated radiotherapy) and concluded that for most patients optimal plans were possible with both techniques. We also found that patient fixation during SRT could be improved by adding a vacuum mouthpiece to the standard stereotactic frame. Five chapters deal with treatment results of SRT in patients with brain metastases. From our own results and a literature review we concluded that single fraction SRT produces excellent local control results in patients with small brain metastases, but insufficient local control rates in patients with large metastases. The higher biologically equivalent doses needed for improved local control rates in large brain metastases can be administered with fractionated SRT. Finally, we studied the clinical problem of lesion growth after SRT of brain metastases. The cause can be real tumor progression or pseudo-progression (radiation toxicity). We found that symptomatic pseudo-progression is serious radiation toxicity of the normal brain tissue surrounding the metastasis. Reduction of pseudo-progression rates is possible by limiting the volume of normal brain tissue that receives high radiation doses.