A Universal Multimodal Female Pelvic Phantom With Brachytherapy Applications

Anthropomorphic phantoms are needed to support training, workflow validation, and imaging studies in gynecologic brachytherapy, particularly in settings with limited access to commercial models. This study describes the design and validation of a low-cost multimodal female pelvic phantom that replicates pelvic anatomy and tissue properties relevant to brachytherapy.

A custom phantom was constructed with embedded uterus, cervix, bladder, rectum/sigmoid, and tumor structures using agar tissue-mimicking materials and three-dimensional (3D) printed molds derived from patient contours. The phantom was designed to be compatible with computed tomography, magnetic resonance imaging, planar ultrasound (US), and 3D transabdominal and transrectal US, and to accommodate standard intracavitary and interstitial applicators. Imaging properties, including speed of sound, Hounsfield units, and electron density, were measured and compared to clinical reference values. Three trained raters performed repeated segmentations on all modalities to assess segmentation properties and variability.

The phantom provided clear visualization of internal structures on all imaging modalities and maintained structural integrity during repeated use and applicator insertion. Measured speed of sound values differed by less than 2.6% from the 1540 m/s reference, with the largest deviation producing an axial measurement uncertainty of 1.3 mm. Hounsfield unit values ranged from 31.7 to 53.4, and electron density values differed by under 0.5% from institutional standards. The most consistent segmentations were produced with magnetic resonance imaging, whereas the greatest variability was observed in 3D transrectal US for small structures. The total material cost to create the phantom was approximately $150 Canadian dollars.

The developed phantom supports realistic brachytherapy applicator placement, multimodal imaging, image segmentation, and has potential for future integration into dose planning studies.