Midline Block (Central Shielding)

In radiotherapy for cervical cancer, because brachytherapy can provide concentrated dose to the primary tumor, midline block (central shielding) has been applied at least partially in external beam therapy to lower the dose to rectum and bladder and avoid severe complications. Although this practice has been decreased over the years globally, the central shielding technique continues to be used as standard in Japan. The use of central shielding in Japan has resulted in relatively low incidence of late complications in the rectum and bladder without compromising the disease control. Recent study of composite dose distributions of the treatment regimen using central shielding revealed its characteristics which explains the benefit of this technique. This chapter will cover the history, philosophy, analysis of composite dose distributions, issues of dose reporting, and the future prospect of this technique.