Dosimetric evaluation of the feasibility of utilizing a reduced number of interstitial needles in combined intracavitary and interstitial brachytherapy for cervical cancer.

Purpose: To evaluate the ability of the Venezia advanced multichannel tandem and ring applicator to consistently produce dosimetrically comparable plans utilizing a reduced number of needle channels, to reduce the risk of secondary complications when boosting cervical cancer treatments with high dose rate (HDR) brachytherapy.

Methods: We evaluated 26 fractions from 13 patients who were treated with HDR brachytherapy using the Venezia (Elekta) applicator. The original plans included a full load of 12-16 needles, including both parallel and 30-degree oblique needles. We replanned each original to nine new configurations, with a reduced number of two, three, four, or six needles. Comparisons included differences in percentage dose coverage to 90% of the high-risk clinical target volume, and percentage dose to 2 cm of the bladder, rectum, sigmoid, and bowel. We considered new plans "passing" if they remained within our standards (D90 > 100%; D2 cm  < 85% bladder, <65% rectum, sigmoid, bowel) or did not perform worse than original.

Results: Removing only the two most anterior or the two most posterior needles from both sides showed 80.8% and 61.5% overall passing rate. Removal of the most anterior and posterior four needles together showed 65.4% overall passing rate. Removing all oblique needles showed 19.2% overall passing rate. Removing only left-sided or only right-sided oblique needles showed 46.2% and 23.1% overall passing, respectively. Removing only right-sided or only left-sided parallel needles separately showed 19.2% and 34.6% overall passing, respectively. Removing all parallel needles showed 11.5% overall passing rate.

Conclusions: As only two replans required a full needle load to maintain dosimetric quality and 40 (76.9%), 36 (34.6%), 18 (69.2%), and 10 (19.2%) replans passed with 2, 3, 4, and 6 needles removed respectively, this indicates the potential for using a lesser number of interstitial needles during combined intracavitary and interstitial HDR brachytherapy while maintaining dosimetric quality.