Point dose variations with time during traditional brachytherapy for cervical carcinoma

In traditional brachytherapy for carcinoma of the cervix, doses are often prescribed to specifically chosen points (A and B) and the normal tissue tolerance calculated at specific reference points in the bladder and rectum. These tolerance doses are often used to modify the brachytherapy treatment plan. It is inherently assumed that the position of the brachytherapy applicator does not change in relation to the relevant anatomical structures over the time-course of an implant. To assess the accuracy of this assumption, 2 sets of localization films were obtained for each implant in 28 patients, 1 prior to loading and another after the removal of the radioactive sources. Significant applicator movement and, consequently, significant dose variations were ob: served. Therefore, isolated one-time dose measurements to normal critical structures should not be used as the sole basis for making therapeutic decisions. The magnitude of dose variations and their clinical significant are discussed.