Background and purpose Clinical introduction of in-house developed medical devices in Europe requires conformity to the Medical Device Regulation (MDR) 2017/745 Article 5(5). Published experience on regulatory aspects of these devices is limited. This work describes our in-house development and verifications of the 3D printed patient-tailored ARCHITECT brachytherapy applicator and accompanying software, prepared to support clinical investigation and in-house use. Materials and methods Article 5(5) mandates an ‘appropriate’ quality management system (QMS) and exempts in-house medical devices from all MDR requirements except general safety and performance requirements (GSPRs). An institutional QMS was available, comprising documented procedures and fill-in templates for all project phases to compile technical documentation. In the first phase, the QMS requires a market analysis to justify the in-house exemption. In the design phase a prototype is developed, to be iteratively improved during manufacturing and verification phases, based on risk evaluations, verification tests, and processing constraints. Documentation is lastly compiled to support clinical investigations and routine use of the device. Results After confirming that no suitable marketed device was available, risk-based design and manufacturing approaches were used to safeguard in-house development. Verifications of material, manufacturing, mechanical safety, cleaning and sterilisation, use and workflow, and compatibility with procedures showed compliance with GSPRs. Simulated dosimetric benefits were observed compared to marketed devices. Conclusion The ARCHITECT applicator was developed in a systematic process, resulting in documented workflows and verification steps. Our approach provides a practical framework for MDR-compliant introduction of in-house equipment and can inform future best practice guidelines.