Design, verification and validation of a spatially confined magnetic nanoparticle thermal therapy device for conformal thermal dose contouring

Abstract

Background: Magnetic nanoparticle thermal therapy (MNTT) can localize heat within tumors, but non-uniform nanoparticle distribution can limit thermal dose coverage. Spatially confined MNTT (SC-MNTT) addresses this limitation by using a static magnetic field (SMF) to suppress heating outside a selected field-free region (FFR). However, SC-MNTT platforms require improved FFR steering and closed-loop temperature control. Purpose: This study developed and validated a low-cost, four-permanent-magnet SC-MNTT platform for spatially selective heating, dynamic FFR steering, and controlled thermal dose delivery in phantom models. Methods: The device combined four permanent magnets, an induction coil, motion and heating control, fiber-optic thermometry, and autotuning proportional-integral-derivative (PID) control. SMF maps and alternating magnetic field (AMF) defined operating conditions. Three-vial verification experiments evaluated spatially selective heating under pulsed AMF exposure. Liver-phantom validation experiments tested pulsed heating and autotuning PID control using prescribed temperature setpoint, a CEM43 target of 8 [min], and a healthy-tissue limit of 39.50 [°C]. Results: The four-magnet configuration shifted the FFR between selected targets and concentrated heating at the intended nanoparticle location. In three-vial experiments, the selected vial reached normalized heating intensity near 1.00, while non-target vials remained lower between 0.09–0.26, corresponding to selective heating with reduced off-target activation. In liver-phantom experiments, autotuning PID control maintained a mean target temperatures 43.44 ± 0.01 [°C], achieved prescribed CEM43 at selected tumor probes, and kept the designated healthy-tissue probe below the safety threshold. Mean overshoot remained below 1.1 [%]. Conclusion: The four-magnet SC-MNTT platform enabled repeatable in-plane FFR steering, spatially confined heating, and closed-loop thermal dose delivery in phantom models.