ADAPT

Abstract

Paranasal sinus cancer in the present, is postoperatively treated with external beam radiation therapy (EBRT). This treatment method enables accurate high radiation dose delivery, it exposes surrounding organs at risk (OARs) to a low-dose radiation bath, contributing to significant negative side effects for overall patient health. High-Dose-Rate (HDR) brachytherapy could theoretically reduce this low-dose exposure due to its more direct dose fall-off (≈ inverse square). However, this treatment method is currently infeasible, because no device exists that can be introduced in the target anatomy without invasive surgery and that can be reliably stabilized within the irregular sinus cavities.

This graduation project investigates the technical feasibility of a minimally invasive, shape-adaptive applicator capable of enabling postoperative HDR brachytherapy in the (para-) nasal sinus cavity. The core design challenge arises from the anatomical discrepancy between the narrow nasal vestibule entrance required for insertion and the larger, (sinus) cavity behind it where stable positioning is needed.

A stakeholder and workflow analysis in collaboration with UMC-Utrecht hospital staff, defined the primary requirements: atraumatic insertion, temporary stabilization, compatibility with existing workflows and protocols, reversibility, and avoidance of additional surgery.
A review of the state-of-the-art materials, practises and mechanisms evaluated hydrogels, shape memory alloys (SMAs), shape memory polymers, and pneumatic systems. The analysis demonstrated that no single mechanism or material satisfies all constraints. Leading to hybrid system strategies combining compliant deployment with more rigid stabilization elements.

Three initial concepts were developed, exploring the solution space of SMA’s, Multi-chamber inflation systems and patient specific inflatables.
During evaluation and synthesis, an existing medical device: The PORGES-14 Foley Cystodrain Inflatable Catheter, inspired a revised design direction. Its manufacturing method and working principles opened interesting prototyping directions, which formed the basis of a redesigned applicator system tailored to head & neck (H&N) anatomy.

The PORGES applicators were used to develop a functional prototype, used in a 3D-printed anatomical phantom derived from anonymized patient data. CT-based dosimetric analysis was conducted in collaboration with the brachytherapy team. Compared to EBRT imaging, the applicator demonstrated:
• Improved conformity of 100% and 200% isodose lines to the clinical target volume (CTV)
• Reduced exposure of healthy tissue to overall radiation
• A visually reduced extent of the low-dose bath
Using both the Conformity Index COIN and the Coverage Index in quantitative evaluation indicated that effective treatment could be achieved in a hypothetical scenario, whilst also highlighting the potential improvements in deployment accuracy, reliability, and repeatability.

The results demonstrate that a minimally invasive, shape-adaptive HDR brachytherapy applicator for intracavitary sinus treatment is technically feasible and clinically promising under controlled conditions. Phantom-testing supports the potential of reduction in low-dose exposure, but clinical validation remains necessary to reach conclusive evidence.

Key recomendations for further development:
To continue toward clinical implementation, the following research directions are recommended:
• Tissue-device interaction studies to assess deformation behavior, patient (dis-)comfort, and positional stability
• Expanded quantitative dosimetric validation across multiple anatomical models and repeated placements
• Mathematical validation model development to reach conclusive evidence
• Optimization of clinical workflow integration, especially focusing on surgical handling and placement