A Study on the Estimation of RIC (Radiation-Induced Conductivity) of Proton Irradiated Polyimide.

The recent expansion of the application environment of power electronics to high-radiation environments will cause the deterioration of insulation materials used in power electronics due to charging caused by cosmic ray irradiation. The charging phenomena should induce malfunctions in power electronics. Therefore, it is important to understand the insulation characteristics of insulation materials irradiated with protons, electrons, etc., to improve the reliability of power electronics. With respect to the above, there are few reports on the RIC (radiation-induced conductivity) of insulation materials irradiated with proton beams. In this paper, we experimentally evaluated the RIC of PI (polyimide) films irradiated with proton beams under various irradiation conditions. We also studied a calculation method to estimate the measured RIC of the PI. As a result, we clarified that the total conductivity of the PI increased under non-penetrating irradiation conditions and saturated under penetrating irradiation conditions. The reason for this is that the higher the irradiation energy, the deeper the maximum proton penetration depth under non-penetrating irradiation conditions. On the other hand, the conductivity characteristics did not change under penetrating conditions because the penetration depth was the same as the sample thickness. We also developed a calculation method to estimate the conductivity of the entire PI irradiated with proton beams. The estimated data calculated by the above method were analytically fitted with the measured data for most irradiation energy conditions. It is suggested that the above calculation method can estimate the conductivity of the entire PI irradiated with proton beams, regardless of penetrating or non-penetrating irradiation, based on the relationship between the RIC and dose rate of the PI irradiated under penetrating conditions. In the future, we will incorporate the results of this study into a computational model of space charge accumulation inside insulation materials to verify the influence of the RIC caused by proton irradiation on space charge accumulation.

Frequency and Temperature-Dependent Space Charge Characteristics of a Solid Polymer under Unipolar Electrical Stresses of Different Waveforms.

In this paper, we studied the space charge phenomena of a solid polymer under thermal and electrical stresses with different frequencies and waveforms. By analyzing the parameter selection method of a protection capacitor and resistor, the newly built pulsed electro-acoustic (PEA) system can be used for special electrical stresses under 500 Hz, based on which the charge phenomena are studied in detail under positive and negative DC and half-wave sine and rectangular wave voltages. Experimental results show that the charge accumulated in the polyimide polymer under DC conditions mainly comes from the grounded electrode side, and the amount of charge accumulated with electric field distortion becomes larger in a high-temperature environment. At room temperature, positive charges tend to accumulate in low-frequency conditions under positive rectangular wave voltages, while they easily appear under high-frequency situations of negative ones. In contrast, the maximum electric field distortion and charge accumulation under both half-wave sine voltages occur at 10 Hz. When the measurement temperature increases, the accumulated positive charge decreases, with a more negative charge appearing under rectangular wave voltages, while a more positive charge accumulates at different frequencies of half-wave sine voltages. Therefore, our study of the charge characteristics under different voltage and temperature conditions can provide a reference for applications in the corresponding environments.

Less intensive surveillance after radical surgery for stage I-III colorectal cancer by focusing on the doubling time of recurrence.

PURPOSE: To propose a new and improved surveillance schedule for colorectal cancer (CRC) patients by focusing on the recurrence rate, resectability, and especially, the tumor doubling time (DT) of recurrent tumors. METHODS: The subjects of this retrospective review were 1774 consecutive patients who underwent radical surgery for stage I-III CRC between January, 2004 and December, 2015. We calculated the DT by measuring the tumor diameter using computed tomography (CT). RESULTS: The median DT for recurrences in the liver, lung, peritoneum, and other locations were 35, 72, 85, and 36 days, respectively, (p < 0.001) and tumor growth rates differed according to the organs where recurrence developed. Multiple linear regression analysis showed that the DT was strongly associated with the relapse-free interval from primary surgery (p < 0.001), and that the DT in patients with recurrence detected ≥ 3 years after primary surgery was longer by 151.1 days than that in patients with recurrence detected within 1 year after primary surgery. We proposed a less intensive surveillance, which achieved an average cost reduction of 32.5% compared with conventional surveillance in Japan. CONCLUSION: We propose a new and more cost-efficient surveillance schedule for CRC surgery patients in the clinical setting.

Impact of Surgical Resection on Metachronous Metastases of Colorectal Cancer According to Tumor Doubling Time.

BACKGROUND/AIM: We aimed to elucidate the prognostic impact of tumor doubling time (DT) and radical surgery when classified by DT in patients with metachronous liver, lung, or peritoneal metastases of colorectal cancer (CRC). PATIENTS AND METHODS: We reviewed the data of 1941 patients who underwent curative surgery for CRC and calculated DT for recurrences using computed tomography. RESULTS: Short DT was an independent prognostic risk factor in liver (p<0.001) and peritoneal (p=0.03) metastases. Survival was significantly better in patients who underwent surgery than in those who did not, both in short and long DT groups in any metastatic organ (p<0.01). Patients with long DT gained significantly better prognostic benefit from surgery than those with short DT in liver (p=0.01) and peritoneal (p=0.04) metastases. CONCLUSION: Surgery is recommended for resectable metastases, especially in patients with liver and peritoneal metastases with long DT.

Prognostic significance of doubling time in patients undergoing radical surgery for metachronous peritoneal metastases of colorectal cancer.

PURPOSE: The doubling times of tumor volume and tumor markers are associated with the prognosis of liver or lung metastases from colorectal cancer (CRC). However, no studies have assessed peritoneal metastases. Therefore, we aimed to elucidate the association between doubling time and the prognosis of patients who underwent radical surgery for metachronous peritoneal metastases of CRC. METHODS: We calculated the tumor doubling times (TDT) of peritoneal metastases and serum carcinoembryonic antigen-doubling times (CEA-DT) in 33 consecutive patients who underwent radical surgery for metachronous peritoneal metastases between January 2006 and April 2017. The impact of short TDT and CEA-DT on overall survival (OS) and relapse-free survival (RFS) was retrospectively reviewed. RESULTS: In long TDT (> 137 days) group, the 5-year OS rate was 74.1% and median OS time was 6.6 years. In long CEA-DT (> 102 days) group, the 5-year OS rate was 50.0% and median OS time was 5.6 years. Conversely, in short TDT (≤ 137 days) and CEA-DT (≤ 102 days) group, the 5-year OS rates and median OS times were both 0.0% and 3.2 years, respectively. In the multivariate analysis, short TDT was an independent risk factor for poor RFS (P = 0.006) and OS (P = 0.010). Similarly, short CEA-DT was also a poor risk factor for RFS (P < 0.001) and OS (P = 0.012). CONCLUSIONS: Short TDT and CEA-DT are independent risk factors for poor OS and RFS after surgery for metachronous peritoneal metastases of CRC. TDT and CEA-DT should be considered when selecting candidates for surgical resection.