The Quest for Optimal Fractionation Schedules in Stereotactic Radiotherapy

In stereotactic radiotherapy (SRT), treatment with a single high dose is usually feasible as it spares the surrounding normal tissues, especially for intracranial lesions. However, single-fraction treatment may not be ideal in terms of efficacy. Single-dose treatment is particularly inefficient for tumors with hypoxia. Generally, tumors with a size of over 1 cm in diameter are considered to contain hypoxic cells, but the radioresistance of hypoxic cells can be partly overcome by fractionation owing to the reoxygenation of hypoxic tumor cells between fractions. In this article, we discuss the radiobiological characteristics of fractionated stereotactic irradiation (STI). And, based on our observations, we recommend that a dose of 54-60 Gy in six-eight fractions delivered two or three times a week for lung and other tumors larger than 2 cm in diameter is the ideal method of SRT.