Distribution of doses to organs at risk in Cervical Cancer High Dose Rate Brachytherapy using Tandem and Ovoids or Vaginal Cylinder

Abstract

Brachytherapy is an integral part of the treatment of cervical cancer. In brachytherapy, the dose delivered to the tissue is determined primarily by the inverse square law thus the dose decreases rapidly as the distance from the source increases. Therefore, an important role in dose distribution is the geometry of the applicator. A patient's anatomy as well as the fact that the patient may have been operated on must also be taken into account when selecting the applicator. The aim of this study was to assess the influence of the type of cervical cancer brachytherapy applicators (tandem and ovoids or vaginal cylinder) on the dose delivered to adjacent organs, urinary bladder, and rectum. The treatment plans of 10 patients with cervical cancer treated by intracavitary brachytherapy were reviewed, and dose distribution data was collected. Prescribed doses were 7 Gy (or 8 Gy)/fractions, and the number of fractions was from 3 to 5, thus cumulative target EQD2 was between 85-90 Gy. Deliveries of doses to the rectum and bladder were controlled within the tolerance ranges. It was found that the selection of the applicator and the doses administered to the bladder and rectum were correlated. Tandem and ovoid applicators produced lower doses in the bladder and rectum by approximately 20% than the vaginal cylinder. The results of this analysis may potentially enable the optimization of dose distribution for organs at risk in each individual clinical situation.