A Novel Adjustable Tandem and Ring Applicator for Improved Dosimetry in Cervical Cancer HDR Brachytherapy.

Abstract

IntroductionCervical cancer brachytherapy requires highly conformal dose delivery while minimizing radiation exposure to surrounding organs at risk. However, conventional tandem and ring applicators are limited by fixed geometry that may not optimally accommodate patient-specific anatomy. The purpose of this work was to evaluate the dosimetric performance of a novel tandem and ring applicator (RTA) featuring adjustable tandem translation relative to the ring, intended to improve organ-at-risk (OAR) sparing while preserving target coverage in high-dose-rate (HDR) brachytherapy for cervical cancer.Methods and MaterialsA novel RTA allowing linear tandem translation within the ring plane was developed to enable patient-specific alignment without altering ring position. Two cervical cancer patients treated with external beam radiotherapy (45Gy/25 fractions) followed by HDR brachytherapy (27.5Gy/5 fractions) were analyzed. Conventional and novel RTAs were sequentially applied to acquire CT-based datasets. Plans were optimized for adequate HR-CTV D90 coverage while minimizing D2cm³ doses to bladder, rectum, sigmoid, and bowel. EQD2 values (α/β = 3 for OARs; 10 for HR-CTV) were compared. Five retrospective cases were replanned using the novel RTA. Point A was redefined as 2cm superior along the tandem from the cervical os and 2cm lateral perpendicular to the tandem axis.ResultsFor patient 1, the novel RTA reduced average daily D2cm³ by 0.54Gy (rectum), 0.78Gy (bladder), and 0.18Gy (sigmoid), with cumulative EQD2 reductions of 2.23Gy, 4.88Gy, and 1.05Gy, respectively. Patient 2 showed daily reductions of 0.52Gy (rectum) and 0.44Gy (bladder), with EQD2 decreases of 3.20Gy and 4.55Gy. HR-CTV EQD2 increased by 1.67Gy. Retrospective plans demonstrated consistent reductions in OAR doses.ConclusionThe novel RTA demonstrated favorable dosimetric trends for OAR sparing while maintaining target coverage in cervical HDR brachytherapy. The revised Point A definition provides a preliminary framework for anatomically consistent dose reporting in flexible tandem configurations.