Second re-irradiation: A delicate balance between safety and efficacy.

Except for straightforward palliative indications such as painful bone metastases, re-irradiation is often characterized by a narrow therapeutic window and the potential for decreased efficacy and increased toxicity, especially if the cumulative total dose from both courses is high. Second re-irradiations tend to pose even bigger challenges and are thus offered in a restrictive manner to highly selected patients on a case-by-case basis. Normal tissue dose constraints are still an area of active investigation. Nevertheless, examples of potentially useful indications have been published. The present review briefly summarizes areas of uncertainty and opportunities for future research. If evidence-based concepts with acceptable side effect profiles can be developed, an increasing number of patients may benefit from additional radiotherapy to previously exposed target volumes.