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Study of a plastic s…
Study of a plastic scintillating plate‑based quality assu…
Introduction: The purpose of this study was to evaluate a plastic scintillating plate‑based beam monitoring system to perform quality assurance (QA) measurements in pencil beam scanning proton beam. 
Methods: Single spots and scanned fields were measured with the high‑resolution dosimetry system, consisting of a plastic scintillation plate coupled to a camera in a dark box at the isocenter. The measurements were taken at 110–190 MeV beam energies with 30° gantry angle intervals at each energy. Spot positions were determined using the plastic scintillating plate‑based dosimetry system at the isocenter for 70–230 MeV beam energies with 30° gantry angle intervals. The effect of gantry angle on dose distribution was also assessed by determining the scanning pattern for daily QA and 25 fields treated with intensity‑modulated proton therapy. 
Results: Spot size, field flatness, and field symmetry of plastic scintillating plate‑based dosimetry system were consistent with EBT3 at all investigated energies and angles. In all investigated energies and angles, the spot size measured was ±10% of the average size of each energy, the spot position measured was within ±2 mm, field flatness was within ±2%, and field symmetry was within ±1%. The mean gamma passing rates with the 3%/3 mm gamma criterion of the scanning pattern and 25 fields were 99.2% and 99.8%, respectively. 
Conclusions: This system can be effective for QA determinations of spot size, spot position, field flatness, and field symmetry over 360° of gantry rotation in a time‑ and cost‑effective manner, with spatial resolution comparable to that of EBT3 film.

Jaehyeon Seo, Myonggeun Yoon*
Department of Bio-Convergence Engineering, Korea University

Kwangzoo Chung, Youngyih Han, Sung Hwan Ahn*
Department of Radiation Oncology, Samsung Medical Center

Youngyih Han
Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul

Seonghoon Jeong
Department of Proton Therapy Center, National Cancer Center, Goyang

Yunhui Jo
Institute of Global Health Technology (IGHT), Korea University

Geon Oh, Yongha Gi, Heehun Sung
Department of BioMedical Engineering, Korea University, Seoul, Republic of Korea

Myonggeun Yoon*
FieldCure Ltd, Seoul, Republic of Korea
Correlation between …
Correlation between impulse magnitude and inhibition of cell…
This study was designed to investigate the correlation between the impulse by dielectrophoretic force applied inside a dividing cell during alternating electric fields therapy and the inhibition of cell proliferation. Distributions of the electric field and dielectrophoretic force inside a dividing cell were calculated using the finite element method of COMSOL Multiphysics. Based on the results, the average magnitude of the impulse by the dielectrophoretic force applied to the cleavage furrow inside a dividing cell placed in various directions was calculated as a function of electric field intensity at an extracellular reference point. The simulation results showed that the average magnitude of the impulse to the cleavage furrow inside a dividing cell ranged from 1.51 × 10−9 to 1.49 × 10−7 N s when tumor treating fields with an intensity ranging from 0.1 to 1 V/cm is applied at an extracellular reference point for 6 h. To verify the relationships between the impulse by the dielectrophoretic force and the inhibition of cell proliferation, the survival fractions of the four cancer cell lines were determined as a function of intensity and time duration of the electric field. The correlation between the magnitude and application time of the electric field and the survival fractions of the four cell lines showed similar trends in vitro. These results suggest that both the dielectrophoretic force and the time required for the force to act are proportionally related to the inhibitory effect on dividing cells, enabling this impulse to be used as a reference to quantify the inhibition of cell proliferation.

Geon Oh, Yongha Gi, Jinyoung Hong
Department of Bioengineering, Korea University, Seoul, Republic of Korea

Geon Oh, Boram Lee*
Department of Radiation Oncology, Inha University School of Medicine, Incheon, Republic of Korea

Yunhui Jo
Institute of Global Health Technology (IGHT), Korea University, Seoul, Republic of Korea 

Jonghyun Kim, Myonggeun Yoon*
FieldCure Ltd., Seoul, Republic of Korea 
Feasibility study of…
Feasibility study of a scintillation sheet-based detector fo…
Purpose: This study evaluated the properties of a scintillation sheet-based dosimetry system for beam monitoring with high spatial resolution, including the effects of this system on the treatment beam. The dosimetric characteristics and feasibility of this system for clinical use were also evaluated. 
Methods: The effects of the dosimetry system on the beam were evaluated by measuring the percentage depth doses, dose profiles, and transmission factors. Fifteen treatment plans were created, and the influence of the dosimetry system on these clinical treatment plans was evaluated. The performance of the system was assessed by determining signal linearity, dose rate dependence, and reproducibility. The feasibility of the system for clinical use was evaluated by comparing intensity distributions with reference intensity distributions verified by quality assurance. 
Results: The spatial resolution of the dosimetry system was found to be 0.43 mm/pixel when projected to the isocenter plane. The dosimetry system attenuated the intensity of 6 MV beams by about 1.1%, without affecting the percentage depth doses and dose profiles. The response of the dosimetry system was linear, independent of the dose rate used in the clinic, and reproducible. Comparison of intensity distributions of evaluation treatment fields with reference intensity distributions showed that the 1%/1 mm average gamma passing rate was 99.6%. 
Conclusions: The dosimetry system did not significantly alter the beam characteristics, indicating that the system could be implemented by using only a transmission factor. The dosimetry system is clinically suitable for monitoring treatment beam delivery with higher spatial resolution than other transmission detectors.

Jaehyeon Seo, Hyunho Lee, Myonggeun Yoon*
Department of Bio-Convergence Engineering, Korea University, Seoul, Republic of Korea

Jaehyeon Seo
Environmental Radioactivity Assessment Team, Korea Atomic Energy Research Institute, Daejeon, Republic of Korea

Hyunho Lee, Sung Hwan Ahn*
Department of Radiation Oncology, Samsung Medical Center, Seoul, Republic of Korea

Myonggeun Yoon*
FieldCure Ltd, Seoul, Republic of Korea 
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