Author ORCID Identifier

Defense Date


Document Type


Degree Name

Master of Science


Radiation Oncology

First Advisor

Dr. William Y. Song

Second Advisor

Dr. Lulin Yuan

Third Advisor

Dr. Tianjun Ma


Lack of standard guidelines for optimal needle insertion during high-dose-rate (HDR) intracavitary-interstitial (IC-IS) brachytherapy of the cervix means a sophisticated and technical skillset of inserting needles next to IC applicators must be developed to enhance plan quality. This study sought to evaluate the performance of two separate direction modulated brachytherapy (DMBT) tandem applicators used in conjunction with one set of novel DMBT ovoids, to effectively obviate the need for IS needles.

A cohort of 32 retrospective clinical HDR brachytherapy plans was re-planned with Varian’s BrachyVision® treatment planning system, using VEGO® inverse optimization algorithm, with dose heterogeneity accounted for through the AcurosBV®. All plans consisted of IC-IS cases, with a range of 2-4 freehand-loaded needles, with an average prescription dose of 709±53 cGy, and with an average high-risk clinical target volume (HRCTV) of 36.73±17.15 cm3. During re-planning, the conventional tandems, ovoids/rings, and all the needles were replaced by one of the two DMBT tandem models of 5.4-mm and 8.0-mm thicknesses and a set of DMBT ovoids. A two-step inverse optimization process was performed to achieve the lowest possible OAR D2cc doses while keeping equivalent target coverage and maintaining the general pear-shaped dose distribution used by the original plans. On average, -48.62±28.83 cGy, -44.32±25.84 cGy, and -41.73±24.35 cGy reductions in D2cc across bladder, rectum, and sigmoid, respectively, were achieved for the 8-mm DMBT tandem-and-ovoids combinations while the average ΔHRCTV-D90 was +4.3±2.9 cGy with an average net increase in total dwell times of 248.54±77.40 seconds at the luxury of avoiding IS needle insertions.


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