LAUSR

Abstract The fundamental principle of external beam radiation therapy is to fit the target volume with a relatively uniform high dose area while limiting the irradiation of neighboring healthy tissues. This is particularly hard to achieve when critical radiosensitive organs (e.g. Spinal cord) are close to the target volume. In general, the dose fall-off is a restricting factor in minimizing dose to nearby critical structures for clinical cases. Therefore the penumbra width reduction is highly important. In this article, we reviewed many available kinds of literature on penumbra reduction in different radiotherapy machines. Also the factors affecting penumbra were investigated.