Movement of the Cervix in After-loading Brachytherapy: Implications for Designing External-beam Radiotherapy Boost Fields

Insertion of the gold grains during pre-treatment EUA is a useful technique in detecting the movement of the cervix. A significant shift in the position of the gold grains was noted in both the x (lateral) and the y (cranial/caudal) axes. These shifts in the cervix can result in under-dosage of the central pelvis when delivering parametrial boosts with the MLS in place on the basis of the brachytherapy check films. When designing the individualised MLS, the resulting under-dosage could be avoided by taking account of the shift in the gold grain markers and allow the delivery of a more homogenous dose to the pelvis.