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Over the past few decades, tetrafluoroethane (TFE, R134a Freon)-based gases have been widely used in the operation of phenolic resistive plate chambers (RPCs) in many high-energy experiments. However, TFE has a high global warming potential (GWP); therefore, a search for new eco-friendly gases to replace traditional TFE-based ones is now unavoidable. In this research, we present cosmic-ray test results of a prototype RPC for the SHiP (search for hidden particles) experiment using 1.6- and 1.4-mm-thick RPC electrodes containing mixtures of various gases, including 1,3,3,3-tetrafluoropropene (HFO1234ze), CO2, iC4H10 and SF6. We compare the performance data gathered with these new gas mixtures with those gathered with a traditional TFE-based gas used for RPCs in compact muon solenoid (CMS) and a toroidal LHC apparatus (ATLAS) experiments. The addition of CO2 to the HFO1234ze-based gas was found to be fairly effective in reducing the working-point high voltage (HVWP) for RPC operation. The results of our experiments lead us to the conclusion that adding 40% CO2 or less, when combined with HFO1234ze-based gas, is conducive to reliable detector performance for SHiP single-gap phenolic RPCs.

This study describes a method that uses a genetic algorithm to select optimal beam angles in proton therapy and evaluates the effectiveness of the proposed algorithm in actual patients. In the use of the genetic algorithm to select the optimal angle, a gene represents the angle of each field and a chromosome represents the combination of beam angles. The fitness of the genetic algorithm, which represents the suitability of the chromosome to the solution, was quantified by using the dose distribution. The weighting factors of the organs used for fitness were obtained from clinical data through logistic regression, reflecting the dose characteristics of actual patients. Genetic operations, such as selection, crossover, mutation, and replacement, were used to modify the population and were repeated until an evaluation based on fitness reached the termination criterion. The proposed genetic algorithm was tested by assessing its ability to select optimal beam angles in three patients with liver cancer. The optimal results for fitness, planning target volume (PTV), normal liver, and skin in the population were compared with the clinical treatment plans, a process that took an average of 36.8 minutes. The dose-volume histograms (DVHs) and the fitness of the genetic algorithm plans did not differ significantly from the actual treatment plans. These findings indicate that the proposed genetic algorithm can automatically generate proton treatment plans with the same quality as actual clinical treatment plans.

The main goals of the Search for Hidden Particles (SHiP) experiment are to observe hidden particles and to run a high-statistics study of tau neutrino events. Two different types of resistive plate chambers (RPCs) will be used in the future SHiP experiment: one for triggers to select the decayed muons emitted via tau neutrino interactions and one for precision time measurements of charged particles, which are expected from the decays of hidden particles. In the present research, we constructed and tested a prototype RPC module to study the fundamental detector performance of the muon trigger RPCs in the tau neutrino detector of the SHiP experiment. The required detector characteristics, such as the intrinsic noise rate, the time response, and the spatial resolution, were proven through the test of the present prototype detector with cosmic muons.

The present study aimed to determine a method for estimating a potential prognostic factor in alternating electric fields for the treatment of solid tumors based on cell survival curves that evaluate cell proliferation capability. In AGS, B16F10, U373, and HPAF-II cancer cell lines, the proportional relationships of the electric field magnitude and the duration of application with the proliferation of cancer cell lines was identified by in vitro alternating current electric field experiments performed under various conditions. A prognostic factor applicable to alternating electric field therapy was developed by identifying proportional relationships of the electric field magnitude and the duration of application with the proliferation of the four cancer cell lines. Through the experimental results, the absorbed energy in tissue has been suggested as a potential prognostic factor in alternating electric field therapy. The absorbed energy in tissue can be used as a reference to quantify the inhibition of cell proliferation related to control, enabling systematic assessment of alternating electric field therapy which, to date, has not been possible.

Tumor-treating fields therapy involves placing pads onto the patient’s skin to create a low-intensity (1 - 3 V/cm), intermediate frequency (100 - 300 kHz), alternating electric field to treat cancerous tumors. This new treatment modality has been approved by the Food and Drug Administration in the USA to treat patients with both newly diagnosed and recurrent glioblastoma. To deliver the prescribed electric field intensity to the tumor while minimizing exposure of organs at risk, we developed an optimization method for the electric field distribution in the body and compared the electric field distribution in the body before and after application of this optimization algorithm. To determine the electric field distribution in the body before optimization, we applied the same electric potential to all pairs of electric pads located on opposite sides of models. We subsequently adjusted the intensity of the electric field to each pair of pads to optimize the electric field distribution in the body, resulting in the prescribed electric field intensity to the tumor while minimizing electric fields at organs at risk. A comparison of the electric field distribution within the body before and after optimization showed that application of the optimization algorithm delivered a therapeutically effective electric field to the tumor while minimizing the average and the maximum field strength applied to organs at risk. Use of this optimization algorithm when planning tumor-treating fields therapy should maintain or increase the intensity of the electric field applied to the tumor while minimizing the intensity of the electric field applied to organs at risk. This would enhance the effectiveness of tumor-treating fields therapy while reducing dangerous side effects.

Quality assurance (QA) for medical linear accelerators is indispensable for appropriate cancer treatment. Some international organizations and western advanced countries provide QA guidelines for linear accelerators. Currently, QA regulations for linear accelerators in Korean hospitals specify a system in which each hospital stipulates its independent hospital-based protocols for QA procedures (HP_QAPs) and conducts QA based on these HP_QAPs while regulatory authorities verify whether items under these HP_QAPs have been performed. However, because this regulatory method cannot guarantee the quality of universal treatment, and QA items with tolerance criteria are different in many hospitals, the presentation of standardized QA items and tolerance criteria is essential. In this study, QA items in HP_QAPs from various hospitals and those presented by international organizations. Concordance rates between QA items for linear accelerators that were presented by the aforementioned organizations and those currently being implemented in Korean hospitals were shown to exhibit a daily QA of 50%, a weekly QA of 22%, a monthly QA of 43%, and an annual QA of 65%, and the overall concordance rates of all QA items were approximately 48%. In comparison between QA items being implemented in Korean hospitals and those being implemented in western advanced countries, concordance rates were shown to exhibit a daily QA of 50%, a weekly QA of 33%, a monthly QA of 60%, and an annual QA of 67%, and the overall concordance rate of all QA items were approximately 57%. The results of this study indicate that the HP_QAPs currently implemented by Korean hospitals as QA standards for linear accelerators used in radiation therapy do not meet international standards. To solve this problem, it is necessary to develop national standardized QA items and procedures for linear accelerators., Comment: 22 pages, 12 tables