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Experimental Characterization of an Innovative Thermo-Brachytherapy Seed for Prostate Cancer Treatment

Taghizadehghahremanloo, Somayeh
http://orcid.org/0000-0003-1891-5869
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1713225756824631

Abstract Details

2024, Doctor of Philosophy, University of Toledo, Physics.
Adjuvant administration of hyperthermia with radiation therapy in the treatment of cancer has been extensively studied in the past five decades. Concurrent use of the two modalities was found to lead to both complementary and synergetic enhancements in tumor management but presents a practical challenge. Their simultaneous administration using the same implantable seed source has recently been established theoretically through magnetically mediated heat induction and the utilization of ferromagnetic materials. Careful consideration, however, showed that regular ferromagnetic alloys lack the power to overcome blood perfusion at clinically measured rates. We characterized the newly developed thermo-brachytherapy (TB) seed that combines a sealed radioactive source with a ferrimagnetic ceramic (ferrite) core, serving as a self-regulating hyperthermia source when placed in an alternating electromagnetic field. A TB seed structure is based on the Low Dose Rate (LDR) brachytherapy seed, with the ability to simultaneously deliver heat to the target. To increase the heat production and uniformity of temperature distribution, we used hyperthermia-only (HT-only) seeds in the empty spaces within already-inserted implantation needles. The heat generation is due to eddy currents circulating in the seeds’ thin metal shell; it depends drastically on the permeability of the core. We identified a soft ferrite material (MnZnFe2O4) as the best candidate for the core, owing to its high iii permeability, the hyperthermia range Curie temperature, adjustable through specific material composition, and a sharp Curie transition. By measuring the magnetic properties of ferrite samples with different compositions, the final core prototype with the optimal parameters was identified. For this purpose, the permeability as a function of temperature was calculated based on measured circuit parameters and material B-H curves. The thickness of the shell enclosing the ferrite core was optimized separately for TB and HT-only seeds, having slightly different dimensions. Heat generation was calculated using the power versus temperature approximation. Finally, the temperature distribution for a realistic prostate LDR brachytherapy plan was modeled with COMSOL Multiphysics for a set of blood perfusion rates found in the literature. The small size of investigated ferrite core samples resulted in demagnetization significantly decreasing the relative permeability from its intrinsic value of ∼ 5000 to about 11 in the range of magnetic field amplitude and frequency values used in the clinical setting. The power generated by the seed dropped sharply as the shell thickness deviated from the optimal value. The optimized TB and HT-only seeds generated approximately 45 mW and 260 mW power, respectively, providing hyperthermia sources sufficient for > 90% volume coverage even for the highest blood perfusion rates. Due to the rapid Curie transition leading to heat self-regulation, no invasive thermometry is required. The toxicity of the normal tissue surrounding the prostate is minimal due to the rapid temperature fall off within a few millimeters distance from a seed. The TB and HT-only seed prototypes presented here were shown to provide sufficient power for concurrent administration of radiation and hyperthermia. In addition to being used as a source for both radiation and heat at the onset of cancer therapy, these implanted seeds would be available for thermal re-treatment of the tumor in case of recurrence, possibly as a sensitizer to systemic therapies or as a modulator of the immune response, without another invasive procedure. Experimentally determined parameters of the ferrite material cores provided in this study open an opportunity for moving the project to preclinical animal evaluations.
David Pearson (Committee Chair)
Ambalanath Shan (Committee Member)
Nikolas Podraza (Committee Member)
Mersiha Hadziahmetovic (Committee Member)
Aniruddha Ray (Committee Member)
177 p.
Medicine; Physics
hyperthermia, permeability, thermo-brachytherapy

Recommended Citations

Citations

  • Taghizadehghahremanloo, S. (2024). Experimental Characterization of an Innovative Thermo-Brachytherapy Seed for Prostate Cancer Treatment [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1713225756824631

    APA Style (7th edition)

  • Taghizadehghahremanloo, Somayeh. Experimental Characterization of an Innovative Thermo-Brachytherapy Seed for Prostate Cancer Treatment. 2024. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1713225756824631.

    MLA Style (8th edition)

  • Taghizadehghahremanloo, Somayeh. "Experimental Characterization of an Innovative Thermo-Brachytherapy Seed for Prostate Cancer Treatment." Doctoral dissertation, University of Toledo, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1713225756824631

    Chicago Manual of Style (17th edition)

toledo1713225756824631
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© 2024, all rights reserved.
This open access ETD is published by University of Toledo and OhioLINK.
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