Introduction:​ Investigations into the shortcomings of current intracavitary brachytherapy (ICBT) technology has lead us to design an Anatomically Adaptive Applicator (A³). The goal of this work was to design and characterize the imaging and dosimetric capabilities of this device. The A³ design incorporates a single shield that can both rotate and translate within the colpostat. We hypothesized that this feature, coupled with specific A³ component construction materials and imaging techniques, would facilitate artifact-free CT and MR image acquisition. In addition, by shaping the delivered dose distribution via the A³ movable shield, dose delivered to the rectum will be less compared to equivalent treatments utilizing current state-of-the-art ICBT applicators.

Method and Materials:​ A method was developed to facilitate an artifact-free CT imaging protocol that used a "step-and-shoot" technique:​ pausing the scanner midway through the scan and moving the A³ shield out of the path of the beam. The A³ CT imaging capabilities were demonstrated acquiring images of a phantom that positioned the A³ and FW applicators in a clinically-applicable geometry. Artifact-free MRI imaging was achieved by utilizing MRIcompatible ovoid components and pulse-sequences that minimize susceptibility artifacts. Artifacts were qualitatively compared, in a clinical setup. For the dosimetric study, Monte-Carlo (MC) models of the A³ and FW (shielded and unshielded) applicators were validated. These models were incorporated into a MC model of one cervical cancer patient ICBT insertion, using ¹⁹²Ir (mHDR v2 source). The A³ shield's rotation and translation was adjusted for each dwell position to minimize dose to the rectum. Superposition of dose to rectum for all A³ dwell sources (4 per ovoid) was applied to obtain a comparison of equivalent FW treatments. Rectal dosevolume histograms (absolute and HDR/PDR biologically effective dose (BED)) and BED to 2 cc (BED_2cc) were determined for all applicators and compared.

Results:​ Using a "step-and-shoot" CT scanning method and MR compliant materials and optimized pulse-sequences, images of the A³ were nearly artifact-free for both modalities. The A³ reduced BED2cc by 18.5% and 7.2% for a PDR treatment and 22.4% and 8.7% for a HDR treatment compared to treatments delivered using an uFW and sFW applicator, respectively.

Conclusions:​ The novel design of the A³ facilitated nearly artifact-free image quality for both CT and MR clinical imaging protocols. The design also facilitated a reduction in BED to the rectum compared to equivalent ICBT treatments delivered using current, state-of-the-art applicators.