• Journal of Gastric Cancer
• /
• 제15권3호
• /
• pp.159-166
• /
• 2015

Purpose: Laparoscopic total gastrectomy (LTG) is more complicated than laparoscopic distal gastrectomy, especially during a surgeon's initial experience with the technique. In this study, we evaluated the short-term outcomes of and learning curve for LTG during the initial cases of a single surgeon compared with those of open total gastrectomy (OTG). Materials and Methods: Between 2009 and 2013, 134 OTG and 74 LTG procedures were performed by a single surgeon who was experienced with OTG but new to performing LTG. Clinical characteristics, operative parameters, and short-term postoperative outcomes were compared between groups. Results: Advanced gastric cancer and D2 lymph node dissection were more common in the OTG than LTG group. Although the operation time was significantly longer for LTG than for OTG ($175.7{\pm}43.1$ minutes vs. $217.5{\pm}63.4$ minutes), LTG seems to be slightly superior or similar to OTG in terms of postoperative recovery measures. The operation time moving average of 15 cases in the LTG group decreased gradually, and the curve flattened at 54 cases. The postoperative complication rate was similar for the two groups (11.9% vs. 13.5%). No anastomotic or stump leaks occurred. Conclusions: Although LTG is technically difficult and operation time is longer for surgeons experienced in open surgery, it can be performed safely, even during a surgeon's early experience with the technique. Considering the benefits of minimally invasive surgery, LTG is recommended for early gastric cancer.

• 공원문화
• /
• 통권26호
• /
• pp.26-32
• /
• 1984

There have been few researches on the factors affecting forest recreation demand and demand for and value of forest recreation in Korea. This study has three main objectives as follows; First, to introduce the nature of recreation demand, the factors affecting forest recreation demand, and the methods of measuring demand for and benefits from forest recreation by reviewing related literatures. Secondly, to investigate the visitors' characteristics, patterns of recreation activities, and their attitudes for the recreation environments at the Deogyu National Park through interviewing them with the questionaire. Thirdly, to estimate the demand for and benefits of forest recreation at the National Park by Travel Cost Method. The survey was dealt by three trained interviewers at the enterance of the park for 5 days from September 26 to October 10, 1982. The 430 respondents were sampled randomly among 9,391 visitors with 4.6% of sampling rate. As the results, the study revealed that most of visitors to Deogyu National Park were from urban areas and belonged to the intermediate-upper income classes, and that most of them traveled more than 250 km or 4 hours to the site from their origins. And more respondents answered that the recreation environments of the cite were more or less better than other recreation areas. From the date of travel distances and participation rates of 13 cities or counties, the demand schedule of forest recreation at the National Park was established. The estimated equation of total experience demand curve is; Log $VR_i$ 2.6353 – 1.021 Log $D_i$ $R^2=0.9451$ where, $VR_i$ $(%\times1000)$ = Participation rate of the ith origin $D_i$ (km) = Travel distance from the ith origin From the total experience demand curve, the demand curve of recreation resources was built by adding travel cost in distance (km). The regression equation of the recreation resources at the Nation park is; Log V = 4.0304 – 0.8167 Log D $R^2=0.9060$ From the demand schedule of recreation resources, the recreational bendfits of Deogyu National Park was estimated. The estimated bendfits to a visitor from the forest is equivalent to the travel cost of 2,372 km. The study also found out that the demand for recreation resources was less elastic than the demand for the total recreation experience at the Deogyu National Park.

• Journal of Gastric Cancer
• /
• 제16권4호
• /
• pp.240-246
• /
• 2016

Purpose: It is hypothesized that robotic gastrectomy may surpass laparoscopic gastrectomy after the operators acquire long-term experience and skills in the manipulation of robotic arms. This study aimed to evaluate the long-term learning curve of robotic distal gastrectomy (RDG) for gastric cancer compared with laparoscopic distal gastrectomy (LDG). Materials and Methods: From October 2008 to December 2015, patients who underwent LDG (n=809) were matched to patients who underwent RDG (n=232) at a 1:1 ratio, by using a propensity score matching method after stratification for the operative year. The surgical outcomes, such as trends of operative time, blood loss, and complication rate, were compared between the two groups. Results: The RDG group showed a longer operative time (171.3 minutes vs. 147.6 minutes, P<0.001) but less estimated blood loss (77.6 ml vs. 116.6 ml, P<0.001). The complication rate and postoperative recovery did not differ between the two groups. The RDG group showed a longer operative time and similar estimated blood loss compared with the LDG group after 5 years of experience (operative time: 159.2 minutes vs. 136.0 minutes in 2015, P=0.003; estimated blood loss: 72.9 ml vs. 78.1 ml in 2015, P=0.793). Conclusions: In terms of short-term surgical outcomes, RDG may not surpass LDG after a long-term experience with the technique.

• 한국산학기술학회논문지
• /
• 제13권11호
• /
• pp.5587-5594
• /
• 2012

불포화토 역학에 있어 흐름특성에 대한 규명은 지반공학적 문제들을 해결하는데 있어 매우 중요하다. 특히, 불포화토의 흐름특성을 모사하기 위한 첫 걸음이 되는 함수특성곡선의 측정을 위해서는 측정자의 오류를 최소화할 수 있는 신뢰성있고 편리한 기법이 필수적으로 요구되어진다. 플로우 펌프 시스템을 포함하여 현재까지 많은 연구자들은 함수특성곡선을 측정할 수 있는 다양한 기법들을 개발하였다. 본 연구에서는 기존에 제안되어진 플로우 펌프시스템을 활용한 흡입력 조절 기법을 이용하여 건조과정과 습윤과정에서 정확하게 실험 공시체의 함수특성곡선을 측정하였다. 플로우 펌프 시스템을 활용한 흡입력 조절 기법을 통하여 두 가지 시료의 함수특성곡선을 산정하였으며, 실험 결과를 바탕으로 흡입력 조절 기법은 현장 조건에 맞는 조건들을 실내에서 구현할 수 있으며 또한 건조과정과 습윤과정에서 발생하는 함수특성곡선의 이력현상을 규명하는데 적절한 장비인 것을 확인하였다. 특히, 플로우 펌프시스템을 활용한 흡입력 조절 기법은 자동화된 장비와 정밀도로 인하여 높은 정확도를 이끌어낼 수 있어 측정오차를 줄임과 동시에 측정시간을 절약하여 함수특성곡선을 측정할 수 있다.

• 신재생에너지
• /
• 제2권4호
• /
• pp.86-92
• /
• 2006

This paper analyses the economics of 50kW PV system installed in Tibet and using domestic technology. We show that this system can be expanded to very large-scale photovoltaic power generation [VLS-PV] system successfully. Based on this result, we conduct the economic analysis of 100MW VLS-PV system designed assuming that it will be installed from 2008 to 2017 in Tibet. In this analysis, future price of PV module and system are estimated based on the methodology of experience curve. In 50kW PV system, the generation cost is calculated at 567.2 won/kWh and this is lower than the one of domestic PV system. In future 100MW VLS-PV system. the generation cost is calculated at 305.4 won/kWh by declining system price. If the lifetime and efficiency of the system goes up, due to future technological improvements, the generation cost can be lowered. Moreover, under the environmental and political effect, VLS-PV system can be as competitive as the conventional energy within 20 years.

• Journal of Gastric Cancer
• /
• 제18권1호
• /
• pp.90-98
• /
• 2018

Purpose: We evaluated the learning curve and short-term surgical outcomes of robot-assisted distal gastrectomy (RADG) performed by a single surgeon experienced in open, but not laparoscopic, gastrectomy. We aimed to verify the feasibility of performing RADG without extensive laparoscopic experience. Materials and Methods: Between July 2012 and December 2016, 60 RADG procedures were performed by a single surgeon using the da $Vinci^{(R)}$ Surgical System (Intuitive Surgical). Patient characteristics, the length of the learning curve, surgical parameters, and short-term postoperative outcomes were analyzed and compared before and after the learning curve had been overcome. Results: The duration of surgery rapidly decreased from the first to the fourth case; after 25 procedures, the duration of surgery was stabilized, suggesting that the learning curve had been overcome. Cases were divided into 2 groups: 25 cases before the learning curve had been overcome (early cases) and 35 later cases. The mean duration of surgery was 420.8 minutes for the initial cases and 281.7 minutes for the later cases (P<0.001). The console time was significantly shorter during the later cases (168.6 minutes) than during the early cases (247.1 minutes) (P<0.001). Although the volume of blood loss during surgery declined over time, there was no significant difference between the early and later cases. No other postoperative outcomes differed between the 2 groups. Pathology reports revealed the presence of mucosal invasion in 58 patients and submucosal invasion in 2 patients. Conclusions: RADG can be performed safely with acceptable surgical outcomes by experts in open gastrectomy.

• Korean Journal of Radiology
• /
• 제20권5호
• /
• pp.844-853
• /
• 2019

Objective: To evaluate the learning curve for C-arm cone-beam computed tomography (CBCT) virtual navigation-guided percutaneous transthoracic needle biopsy (PTNB) and to determine the amount of experience needed to develop appropriate skills for this procedure using cumulative summation (CUSUM). Materials and Methods: We retrospectively reviewed 2042 CBCT virtual navigation-guided PTNBs performed by 7 novice operators between March 2011 and December 2014. Learning curves for CBCT virtual navigation-guided PTNB with respect to its diagnostic performance and the occurrence of biopsy-related pneumothorax were analyzed using standard and risk-adjusted CUSUM (RA-CUSUM). Acceptable failure rates were determined as 0.06 for diagnostic failure and 0.25 for PTNB-related pneumothorax. Results: Standard CUSUM indicated that 6 of the 7 operators achieved an acceptable diagnostic failure rate after a median of 105 PTNB procedures (95% confidence interval [CI], 14-240), and 6 of the operators achieved acceptable pneumothorax occurrence rate after a median of 79 PTNB procedures (95% CI, 27-155). RA-CUSUM showed that 93 (95% CI, 39-142) and 80 (95% CI, 38-127) PTNB procedures were required to achieve acceptable diagnostic performance and pneumothorax occurrence, respectively. Conclusion: The novice operators' skills in performing CBCT virtual navigation-guided PTNBs improved with increasing experience over a wide range of learning periods.

• Communications for Statistical Applications and Methods
• /
• 제19권3호
• /
• pp.433-450
• /
• 2012

연구자가 같은 작업을 반복적으로 수행할 때, 작업 효율성은 연구에 관련된 지식, 경험, 기술이 축적되면서 향상된다. 결과를 얻기 위해 연구에 투자하는 시간은 같은 작업을 반복함으로써 줄일 수 있다. 이러한 현상을 학습곡선 효과(learning curve effect)라고 일컫는다. 학습곡선(learning curves)은 학습의 변화를 시각적으로 나타낸 것으로 이전의 학습곡선 연구에서는 시간을 일정한 구간으로 나누어 구간별 작업에 대한 숙련도의 평균 차이 여부를 확인하였다. 이러한 방법은 구간을 어떻게 나눌 것인가 하는 기준이 존재하지 않으며, 더욱이 이항 반응 자료로 모형을 적합하기 어려운 문제점을 가지고 있다. 본 연구에서는 이산형 확률변수 중 이항 반응 자료(베르누이자료)에 대한 학습곡선의 통계적 모형에 초점을 맞추고자 한다. 누적확률분포의 특성을 이용하여 모수를 추정하기 위해서 뉴튼-랩슨 방법(Newton-Raphson method)을 사용하였고, 이 연구에서 제안한 모형의 점근적 분포를 구하였다.

• Journal of Gastric Cancer
• /
• 제18권2호
• /
• pp.172-181
• /
• 2018

Purpose: This study aimed to evaluate the surgical outcomes and investigate the feasibility of reduced-port laparoscopic gastrectomy using learning curve analysis in a small-volume center. Materials and Methods: We reviewed 269 patients who underwent laparoscopic distal gastrectomy (LDG) for gastric carcinoma between 2012 and 2017. Among them, 159 patients underwent reduced-port laparoscopic gastrectomy. The cumulative sum technique was used for quantitative assessment of the learning curve. Results: There were no statistically significant differences in the baseline characteristics of patients who underwent conventional and reduced-port LDG, and the operative time did not significantly differ between the groups. However, the amount of intraoperative bleeding was significantly lower in the reduced-port laparoscopic gastrectomy group (56.3 vs. 48.2 mL; P<0.001). There were no significant differences between the groups in terms of the first flatus time or length of hospital stay. Neither the incidence nor the severity of the complications significantly differed between the groups. The slope of the cumulative sum curve indicates the trend of learning performance. After 33 operations, the slope gently stabilized, which was regarded as the breakpoint of the learning curve. Conclusions: The surgical outcomes of reduced-port laparoscopic gastrectomy were comparable to those of conventional laparoscopic gastrectomy, suggesting that transition from conventional to reduced-port laparoscopic gastrectomy is feasible and safe, with a relatively short learning curve, in a small-volume center.

• Asian Pacific Journal of Cancer Prevention
• /
• 제15권13호
• /
• pp.5395-5399
• /
• 2014

Purpose: This study was designed to evaluate the outcomes of laparoscopic colorectal resection in a period of learning curve completed by surgeons with different experience and aptitudes with a view to making clear whether seniors had a better learning curve compared with juniors. Methods: From May 2010 to August 2012, the first twenty patients underwent laparoscopic colorectal resection completed by each surgeon were selected for analysis retrospectively. A total of 240 patients treated by 5 seniors and 7 juniors were divided into the senior group (n=100) and the junior group (n=140). The short-term outcomes of laparoscopic surgery of the two groups were compared. Results: The mean numbers of lymph nodes harvested were $21.2{\pm}11.0$ in the senior group and $17.3{\pm}11.5$ in the junior group (p=0.010); The mean operative times were $187.9{\pm}60.0min$ as compared to $231.3{\pm}55.7min$ (p=0.006), and blood loss values were $177.0{\pm}100.7ml$ and $234.0{\pm}185ml$, respectively (p=0.001); Conversion rate in the senior group was obviously lower than in the junior group (10.0% vs 20.7%, p=0.027) and the mean time to passing of first flatus were $3.3{\pm}0.9$ and $3.8{\pm}0.9$ days (p=0.001). For low rectal cancer, the sphincter preserving rates were 68.7% and 35.3% (p=0.027). Conclusions: Seniors could perform laparoscopic colorectal resection with relatively better oncological outcomes and quicker recovery, and seniors could master the laparoscopic skill more easily and quickly. Seniors had a better learning curve for laparoscopic colorectal cancer resection compared to juniors.