An anthropomorphic deformable phantom of the vaginal wall and cavity

Brachytherapy is a common treatment in cervical, uterine and vaginal cancer management. The technique is characterised by rapid developments in the fields of medical imaging, dosimetry planning and personalised medical device design. To reduce unnecessary burden on patients, assessments and training of these technologies should preferable be done using high-fidelity physical phantoms. In this study, anthropomorphic deformable phantoms of the vaginal wall and cavity were developed for image-guided adaptive brachytherapy, in which vaginal wall biomechanics were mimicked. Phantoms were produced from both silicone and polyvinyl alcohol materials. Material characterisations were performed with uniaxial tensile tests, via which Young's moduli and toughness were quantified. In addition, the contrast between adjacent phantom layers was quantified in magnetic resonance images. The results showed that stress-strain curves of the silicone phantoms were within the range of those found in healthy human vaginal wall tissues. Sample preconditioning had a large effect on Young's moduli, which ranged between 2.13 and 6.94 MPa in silicone. Toughness was a more robust and accurate metric for biomechanical matching, and ranged between 0.23 and 0.28 ·10⁶J·m^-3as a result of preconditioning. The polyvinyl alcohol phantoms were not stiff or tough enough, with a Young's modulus of 0.16 MPa and toughness of 0.02 ·10⁶J·m^-3. All materials used could be clearly delineated in magnetic resonance images, although the MRI sequence did affect layer contrast. In conclusion, we developed anthropomorphic deformable phantoms that mimic vaginal wall tissue and are well visible in magnetic resonance images. These phantoms will be used to evaluate the properties and to optimise the development and use of personalised brachytherapy applicators.