1. 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

2. 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

3. 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.

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

5. 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

6. 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

7. 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

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

9. 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

10. 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

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

12. 3D Calculation of Magnetic Field
Flux 3D program

13. 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

14. Temperature in Fluxtrol 50 Concentrator (2D Simulation)

15. Temperature in Fluxtrol 50 (3D Simulation)
T = C

16. 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

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

18. 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

19. 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

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