Rationale for Fractionated and Single-Session Approaches

Stereotactic radiosurgery (SRS) delivers a high dose of radiation to an intracranial target in a single session. Modern planning capabilities and the ability to confirm and reproduce day-to-day setup positioning with on-board imaging and customized, relocatable immobilization devices give SRS accuracy and precision to less than a millimeter. Consequently, SRS can be employed effectively in the treatment of small intracranial lesions with little to no toxicity. However, it is unavoidable that some amount of normal tissue will receive a potentially clinically relevant dose, with the risk of unacceptable toxicity increasing with target size and location. In these situations, treating a patient with a more fractionated course, termed hypofractionated-SRS (HF-SRS), has emerged as an alternative approach. The following chapter will address the rationale for choosing HF-SRS over single-fraction SRS, discussing both the radiobiological basis for this choice and pertinent clinical data related to toxicity and efficacy. Though this chapter will focus on findings related to the treatment of intracranial targets, the principles discussed can be applied more broadly to the treatment of lesions in the body.