Computational analysis of the impact of urine volume on magnetic nanoparticle hyperthermia in the treatment of non-muscle-invasive bladder cancer.

Magnetic nanoparticle hyperthermia (MNP-HT) has emerged as a promising non-invasive technique for targeted cancer therapy. This study presents a comprehensive computational analysis of the influence of urine volume on the efficacy of MNP-HT for the treatment of T1 non-muscle-invasive bladder cancer (NMIBC). A two-dimensional axisymmetric finite element model was developed, coupling solid tissue heat transfer with intravesical fluid dynamics. Magnetite (Fe3O4) nanoparticles with a mean diameter of 19 nm were excited using an alternating magnetic field at a frequency of 100 kHz. Four clinically relevant urine volumes (60, 120, 240, and 400 mL) were simulated to evaluate their effects on magnetic field distribution, nanoparticle power dissipation, convective heat transfer, and temperature distributions in both tumor and surrounding healthy tissues. Tissue heating was modeled using the Pennes bioheat equation, while urine flow and thermal transport were governed by the Navier-Stokes and energy equations. The results demonstrate a clear inverse relationship between urine volume and hyperthermia efficiency. Average tumor temperatures decreased from 41.89 °C at 60 mL to 41.51 °C at 400 mL due to enhanced convective cooling and reduced magnetic field-dependent nanoparticle power dissipation, while healthy tissue temperatures remained within safe therapeutic limits. These findings highlight urine volume as a critical physiological parameter influencing MNP-HT performance. To optimize thermal efficacy, clinical protocols should aim to minimize bladder urine volume before and during treatment through bladder emptying strategies and careful monitoring of bladder refilling.