ABSTRACT
A general tenet of radiation oncology is that with increased fraction size, there is greater risk of late normal tissue complication. While penumbra is not a clinically signi‚cant issue for low-dose standard fractionated therapy, at high doses of SRS/hSRT, the penumbra dose becomes clinically signi‚cant and can be damaging to healthy tissue, possibly leading to radiation necrosis. With SRS/hSRT, stereotactic techniques are used to minimize the volume of normal tissue exposed to deleterious doses, mitigating but not eliminating early as well as late toxicity risk. e historically used linear quadratic (LQ) model may be less predictive of normal tissue e‰ects after SRS/hSRT, likely due to di‰erent biologic mechanisms with high-dose per fraction schedules (Milano et al., 2011), although this is controversial (Shuryak et al., 2015). e linear quadratic model is derived from in vitro cell survival assays of cancer cell lines, and it has been shown to be clinically predictive at low-dose per fraction treatment. is model is not necessarily expected to predict in vivo toxicity with increased fraction sizes to normal tissues for which injury of di‰erent cell
Contents 19.1 Introduction 295 19.2 Symptoms and Endpoints 296 19.3 Factors A‰ecting Necrosis Risk 296 19.4 Corticosteroid Use in the Management of Brain Necrosis 304 19.5 Warfarin, Pentoxifylline, and Vitamin E 305 19.6 Bevacizumab in the Treatment and Prevention of Central Nervous System
Radiation Necrosis 305 19.7 Hyperbaric Oxygen 306 19.8 Surgical Removal of Brain Necrosis 307 19.9 Fractionation 308 19.10 Conclusion 309 Acknowledgment 310 References 310
types and varied intracellular components may be of increased relevance (Glatstein, 2008). e doses needed to sterilize tumor cells in vitro are much higher than the doses to attain long-term control of metastasis of similar size using SRS.
