SU-E-T-491: Influence of Applicator Dimensions On Doses to Bladder, Rectum and Sigmoid in HDR Brachytherapy for Cervical Cancer

Authors


Abstract

Purpose:

To study the influence of dimensions of the tandem and ring applicator on bladder D2cc, rectum D2cc and sigmoid D2cc in HDR treatment planning for cervical cancer.

Methods:

53 plans from 13 patients treated at our institution with the tandem and ring applicator were retrospectively reviewed. Prescription doses were one of the following: 8 Gy × 3, 7 Gy × 4 and 5.5 Gy × 5. Doses to the D2ccs of the bladder, rectum and the sigmoid were recorded. These doses were normalized to their relative prescriptions doses. Correlations between the normalized bladder D2cc, rectum D2cc and sigmoid D2cc were investigated and linear regression models were developed to study the dependence of these doses on the ring diameter and the applicator angle.

Results:

Normalized doses to the D2cc of the bladder, rectum and sigmoid showed statistically significant correlation (P < 0.05) to the applicator angle. Significant correlation was also noted for the normalized D2cc of the rectum and the sigmoid with the ring diameter. The normalized bladder D2cc was found to decrease with applicator angle on an average by 22.65% ± 4.43% while the same for the rectum and sigmoid were found to increase on an average by 14.43% ± 1.65% and 14.01% ± 1.42% respectively. Both the rectum and sigmoid D2cc reduced with increasing ring diameter by 12.93% ± 1.95% and 11.27% ± 1.79%. No correlation was observed between the normalized bladder D2cc and the ring diameter.

Conclusion:

Preliminary regression models developed in this study can potentially aid in the choice of the appropriate applicator angle and ring diameter for tandem and ring implant so as to optimize doses to the bladder, rectum and sigmoid.

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