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Low Energy X-ray Radiosensitization Activated with High-Z Elements
Author Info
Lim, Sara Gail Ng
Permalink:
http://rave.ohiolink.edu/etdc/view?acc_num=osu1415716030
Abstract Details
Year and Degree
2014, Doctor of Philosophy, Ohio State University, Biophysics.
Abstract
Radiosensitization of biological material such as cancer cells by heavy elements (high atomic number Z or HZ) has been studied as a possible means to improve radiation therapy and imaging for the diagnosis and treatment of cancer. In particular, the energy deposition by low vs. high energy X-rays (LEX & HEX, respectively) has been compared. Computations and simulations have shown that LEX interact favorably with HZ sensitizers by depositing more energy. In contrast, HEX interact predominantly by photon scattering regardless of Z of both the target and sensitizer. Monte Carlo simulations have shown that in comparison to unsensitized tissue models, irradiation of HZ sensitized models resulted in up to a factor of 2 enhancement in dose deposition when performed with LEX, while in contrast dose enhancement with HEX resulted in ~1.2 increase. To verify the computational studies,
in vitro
experiments were performed with two Pt-based sensitizers, carboplatin and a newly developed terpyridine platinum compound, Typ-Pt, and two different cancer models, the F98 rat glioma and B16 mouse melanoma as models for brain and skin cancer respectively. In agreement with the simulations, the
in vitro
experimental studies demonstrated decreased survival of HZ-sensitized cells irradiated with LEX compared to HEX. In addition, fundamental physics involving resonant absorption and fluorescence of monochromatic X-rays also was explored, with potential radiotherapeutic applications. Due to the very high probabilities for interaction at resonant X-ray energies, the amount of radiation damage at the site of the tumors could be significantly higher even in comparison to LEX. Promising but preliminary experiments were performed both on detecting resonant fluorescence at synchrotron X-ray intensities, and on the development of a broadband-to-monochromatic X-ray converter. The converter consists of using low energy broadband X-rays to preferentially ionize the K-shell electrons of a target, resulting in essentially monochromatic K-alpha X-rays equivalent to the energy of the L--->K transition of the target element. The resulting conversion efficiency is comparable to that produced by X-rays from high-intensity lasers, with potential applications in imaging. The resonance fluorescence experiment was conducted at the European Synchrotron Research Facility (ESRF) in Grenoble, France on a 200 micrometer thick tungsten (W) target, irradiated with monochromatic X-rays at and above the K-alpha energy at an angle of 40
o
corresponding to forward scattering and 140
o
to backscattering. In this dissertation, it has been shown that HZ radiosensitization is more effective with LEX, and pathways have been explored for the use of monochromatic X-rays to improve radiation therapy.
Committee
Anil Pradhan , Ph.D. (Advisor)
Rolf Barth, M.D. (Committee Member)
Nilendu Gupta, Ph.D. (Committee Member)
Michael Tweedle, Ph.D. (Committee Member)
Pages
174 p.
Subject Headings
Biophysics
;
Radiation
Keywords
Cancer radiotherapy
;
X-ray imaging
;
X-ray propagation
;
Heavy element sensitization
;
Bio-medical environment
;
In vitro experiments
;
Resonant excitation and fluorescence
;
Broadband-to-Monochromatic X-rays
;
Synchrotron experiments
Recommended Citations
Refworks
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RIS
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Citations
Lim, S. G. N. (2014).
Low Energy X-ray Radiosensitization Activated with High-Z Elements
[Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1415716030
APA Style (7th edition)
Lim, Sara.
Low Energy X-ray Radiosensitization Activated with High-Z Elements.
2014. Ohio State University, Doctoral dissertation.
OhioLINK Electronic Theses and Dissertations Center
, http://rave.ohiolink.edu/etdc/view?acc_num=osu1415716030.
MLA Style (8th edition)
Lim, Sara. "Low Energy X-ray Radiosensitization Activated with High-Z Elements." Doctoral dissertation, Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1415716030
Chicago Manual of Style (17th edition)
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Document number:
osu1415716030
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Copyright Info
© 2014, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.