Generation of Uniform Magnetic Field for Cancer Hyperthermia Research V. Nemkov, R. Goldstein, J. Jackowski – Fluxtrol Inc., Michigan, USA T. L. DeWeese, R. Ivkov - Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine

Overview Heat as Therapeutic Agent Specifications for the Inductor Coil types Magnetic Field Distributions for 2D and 3D models Parameter Comparison of the Coils Temperature Distribution in Magnetic Controller Conclusions

Heat as a Therapeutic Agent Time and temperature define dose There are three strategies of using heat: 1. Heat only – Hyperthermia 2. Heat + Radiation 3. Local heating of inserted nanoparticles - Nanotherapy 3 Dewey, et al.

Heat Sensitizes Cancer to Radiation Hedayati, Zhou, Zhang, DeWeese, Ivkov 4

Heat Generation in Nanoparticles Heat output is amplitude and frequency dependent Heat generation (SAR) depends on concentration also Therapeutic consistency requires homogeneous flux density 5 5

Requirements for Magnetic Heating (“Smart”) Particles must be localized specifically to sites Device must produce consistent field to cover large region of tissue Tissue heating by eddy currents must be tolerable/manageable Extensive tests of cell culture heating using nanoparticles are required for appropriate methodology development 6 6

Small Animal/Cell Culture Coil Goal: Design an inductor even flux density within a 86 x 127mm cross-section region for heating of culture specimens The region of concern is a specimen holding dish (24 or 96-well plate) Frequency must be 150 kHz Max field strength Hm=500 Oe Thermal influence of the coil on the cell vessel must be minimal 7

Helmholtz Coil D H D = 2H Flux 2D simulation

Design of Inductor with Concentrator Challenges: - 3D System - Intensive heating of materials due to combination of strong field, high frequency and long duty time Steps: Definition of dimensions of the inductor with required space of the uniform field Inductor design and parameters calculation Temperature calculation of the concentrator Coil modification to obtain acceptable T Coil manufacturing and tests 9

Concept of Induction Coil Cooling plate Coil tubes Magnetic controller Coil “opening” dimensions: A x B x H = 110 x 175 x 40 mm A

Flux Density Map of Rectangular Coil with Magnetic Controller Flux 2D program

3D Calculation of Magnetic Field Flux 3D program

Induction Coil Parameters Coil Type Concentr. Material Programme Bm Gs U V I kA S MVA PCu kW PConc PTot Helmholtz None Flux 2D 400 1750 8.4 14.7 74 N/A Rectangular Fluxtrol 50 650 4.2 2.7 23 ~ 8.0 31 Flux 3D 720 3.4 2.4 26 34

Temperature in Fluxtrol 50 Concentrator (2D Simulation)

Temperature in Fluxtrol 50 (3D Simulation) T = 131-138 C

Further Expected Improvements Improved Magnetic Controller Material Controller Design with Account of Anisotropy Coil Copper Geometry Optimization Controller Application Technique Improvement Pressing direction Thermal anisotropy λZ < λX = λY Z Y X

Equipment and Facility Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine 17 17

Summary Design of induction system with uniform field for large cell-well plates exposure to uniform field is a challenging task Helmholtz coils require much higher reactive power (5x), active power (2x), voltage and current than a special coil with magnetic concentrator 2D computer simulation resulted in overevaluation of coil current (24%), underevaluation of voltage (10%) for required field strength compared to 3D simulation 18

Summary 3D effects lead to significant increase of the magnetic controller temperature Results of the coil tests were in good agreement with predicted Further design improvement is coming Special attention must be paid to magnetic material selection, orientation and application technique 19

Acknowledgement This work was funded by a grant from the Prostate Cancer Foundation