Age and life history of an old black pine (Pinus thunbergii Parl.) tree at Cave Temple on Mt. Sanbangsan, Jeju Island, Korea, died due to pine wilt disease in 2013

Kim, Eun-Shik,Lee, So-Hee,Kim, Joon-Bum,Kim, Chan-Soo,Yoon, Bong-Taek,Lee, Sung-Hoon,Lim, Wontaek,Kim, Hyojung,Choi, Junghwan,Han, Hyerim The Ecological Society of Korea 2015 Journal of Ecology and Environment Vol.38 No.1

In 2013, the epidemics of pine wilt disease caused by the pine wood nematodes (Bursaphelenchus xylophilus) resulted in damages to the forests of black pine (Pinus thunbergii Parl.) trees in Jeju Island, Korea. Among the affected trees, an old black pine tree at Cave Temple on Mt. Sanbangsan was included and died due to the prevalence of pine wilt disease. The tree was on Mt. Sanbangsan, which was designated as a National Scenic Place with the Number 77 and was believed to be more than 400 years old in age. By examining the disc of the tree stem obtained from the height of 2 m, we counted the tree rings from 4 different directions and cross-dated the readings by comparing the records of drought simulated from the BROOK Model. Our analysis indicates that the tree seems to have grown since late 1860s. Contrary to the belief of the general public, we can conclude that the age of the tree was estimated to be at maximum 150 years, which means that it was not the same old tree as was shown in the painting of the Tam-Ra-Sun-Ryeok-Do (an old painting book for the Inspection Tour of Jeju Island) published in 1702. Discussion was extended to the life history of the tree in growth and leaning and the measures to protect the tree species from the damages of the pine wilt disease caused by pine wood nematodes.

Adaptive Image Rescaling for Weakly Contrast-Enhanced Lesions in Dedicated Breast CT: A Phantom Study

Kim Bitbyeol,Kim Ho Kyung,Kim Jinsung,Ki Yongkan,Joo Ji Hyeon,전호상,Park Dahl,Kim Wontaek,Nam Jiho,Kim Dong Hyeon 대한영상의학회 2021 대한영상의학회지 Vol.82 No.6

Purpose Dedicated breast CT is an emerging volumetric X-ray imaging modality for diagnosis that does not require any painful breast compression. To improve the detection rate of weakly enhanced lesions, an adaptive image rescaling (AIR) technique was proposed. Materials and Methods Two disks containing five identical holes and five holes of different diameters were scanned using 60/100 kVp to obtain single-energy CT (SECT), dual-energy CT (DECT), and AIR images. A piece of pork was also scanned as a subclinical trial. The image quality was evaluated using image contrast and contrast-to-noise ratio (CNR). The difference of imaging performances was confirmed using student’s t test. Results Total mean image contrast of AIR (0.70) reached 74.5% of that of DECT (0.94) and was higher than that of SECT (0.22) by 318.2%. Total mean CNR of AIR (5.08) was 35.5% of that of SECT (14.30) and was higher than that of DECT (2.28) by 222.8%. A similar trend was observed in the subclinical study. Conclusion The results demonstrated superior image contrast of AIR over SECT, and its higher overall image quality compared to DECT with half the exposure. Therefore, AIR seems to have the potential to improve the detectability of lesions with dedicated breast CT.

Utility of split-VMAT for cardiac protection during left breast cancer radiotherapy

Kim Dong Woon,Jeon Hosang,Ki Yongkan,Joo Ji Hyeon,Kim Wontaek,Kim Donghyeon,Park Dahl,Nam Jiho 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.5

The feld-in-feld technique of three-dimensional conformal radiotherapy (3D-CRT) is a common treatment technique used in breast radiation therapy. However, when the heart is largely included in the treatment feld for the treatment of left breast cancer, it is unavoidable that a large dose will impact the heart. Increases in the mean dose and the maximum dose to the heart increase the hazard ratio for ischemic heart disease. Split-VMAT is a technique that combines tangential feld and volumetric modulated arc therapy (VMAT) methods using multiple small partial arcs. Split-VMAT can reduce the maximum dose to the heart and while ensuring target coverage. In this study, we sought to confrm the utility of split-VMAT for patients with left breast cancer whose heart is more than 1 cm inside the treatment feld. The split-VMAT plan consisted of 4 felds, set at 20–60° per feld, and the treatment time was limited to less than 20 s to enable deep-inspiration breath hold (DIBH). A half-VMAT, consisting of an arc of 180° and a feld-in-feld approach, using 2 tangential felds symmetrical to each other, were used as comparison groups. In addition, the feld-in-feld technique was divided into 2 types, 1 that emphasized target coverage and the other that focused on heart protection. For treatment, an Elekta Versa HD linear accelerator was used, and treatment planning was performed using Elekta Monaco software. Both split-VMAT and feld-in-feld, focused on target coverage achieved better (>3%) target coverage. However, in feld-in-feld, focused on target coverage, the maximum dose to the heart was very high. Compared to the both feld-in-feld-based technique, the average dose to the lungs was about twice as high in the both VMAT-based technique. In addition, the treatment time per feld was increased by about 5 s, and the total treatment time was more than doubled. The 3D-CRT feld-in-feld technique can signifcantly protect organs at risk (OARs) not included in the radiation feld because the gantry is not directed to inside the body. However, if the heart is, the OAR, it may be exposed to high radiation doses. The split-VMAT limits the angle of the arc, constraining the beam directed inside the patient's body, and shortens the treatment time to allow DIBH. In addition, since sufcient target coverage and heart protection are possible, split-VMAT can be a compromise between 3D-CRT, intensity-modulation radiotherapy, and conventional VMAT.

Disturbance in seedling development of Korean fir (Abies koreana Wilson) tree species on higher altitude forests of Mt. Hallasan National Park, the central part of Jeju Island, Korea

Kim, Eun-Shik,Lee, Jong-Won,Choi, Im-Joon,Lim, Wontaek,Choi, Junghwan,Oh, Choong Hyeon,Lee, Sung-Hoon,Kim, Young-Sun The Ecological Society of Korea 2017 Journal of Ecology and Environment Vol.41 No.6

Background: Natural regeneration of seedlings as well as saplings of Korean fir has been significantly impacted by the browsing from the early stages of their development, potentially, by roe deer for the last two to three decades at the study site since late 1980s. This study was carried out to investigate current status of the disturbance in the seedling development of Korean fir (Abies koreana) on Mt. Hallasan, Jeju Island, Korea. Methods: Field survey was carried out during June and August in 2016 to measure the characteristics of study site and understory vegetation by applying systematic sampling to 125 plots of $5m{\times}5m$ quadrat located on eastern slope of the mountain. Correlation and regression analyses were applied to the variables quantified from the data sets using the SAS software. Results: No saplings with their diameters at breast heights smaller than 5.0 cm were found at the study site indicating the serious disturbance in the natural regeneration of Korean fir at the study site. No seedlings with their heights taller than 36.0 cm were found at the study site indicating even more serious disturbance during earlier stage of the natural regeneration of Korean fir at the study site. A total of 616 individuals of the seedlings of Korean fir were found at 54 out of 125 sampling plots. One hundred thirty-eight seedlings (22.4%) out of 616 individual seedlings have the vestiges for being grazed, potentially, by roe deer. Conclusions: Due considerations should be given to the effects of browsing of the seedlings by roe deer to promote the natural regeneration of Korean fir, ultimately to restore Korean fir. It is needed for the managers of the forest to install fences around the forest area. Exclosure experiments as well as enclosure experiments of different densities of browsing should be carried out. In addition, treatment with different densities of Jeju dwarf bamboo should also be included in the experiment on Mt. Hallasan National Park, Jeju Island, Korea.

Adjuvant external beam radiation and brachytherapy for vaginal resection margin positive cervical cancer

Kim, Donghyun,Ki, Yongkan,Kim, Wontaek,Park, Dahl,Lee, Joohye,Lee, Jayoung,Jeon, Hosang,Nam, Jiho The Korean Society for Radiation Oncology 2018 Radiation Oncology Journal Vol.36 No.2

Purpose: To evaluate the treatment outcomes of adjuvant external beam radiation therapy (EBRT) and vaginal brachytherapy (VB) following radical hysterectomy in cervical cancer patients with involved vaginal resection margin (VRM). Materials and Methods: We retrospectively reviewed the medical records of 21 patients treated with postoperative EBRT and VB for positive VRM FIGO stage IB-IIA cervical cancer between 2003 and 2015. Concurrent platinum-based chemotherapy was administered to all patients. Results: The median whole pelvis EBRT dose was 50.4 Gy (range, 45 to 50.4 Gy). In the VB, the median dose per fraction, number of fractions, and total dose delivered were: 4 Gy (range, 3.0 to 4.0 Gy), 4 fractions (range, 3 to 5 fractions), and 16 Gy (range, 12 to 20 Gy), respectively. At a median follow-up of 46 months (range, 9 to 122 months), local recurrence was observed in 2 patients, and distant metastasis was present in 7 patients. All patients with local recurrence subsequently developed distant metastases. The 5-year local control, disease-free survival, and overall survival rates were 89.1%, 65.9%, and 62.9%, respectively. Of the 21 patients, 7 patients (33.3%) reported grade 2 acute toxicity; however, there were no grade 3 or higher acute adverse events. Grade 1-2 late toxicities were observed in 8 patients. Late grade 3 urinary toxicity was reported in 1 patient. Conclusions: Adjuvant EBRT and VB showed excellent local control and low toxicity in cervical cancer patients with positive VRM. Although limited by its retrospective nature, the findings from our study provide evidence supporting the use of additional VB in pathologically involved VRM.

Adjuvant external beam radiation and brachytherapy for vaginal resection margin positive cervical cancer

Donghyun Kim,Yongkan Ki,Wontaek Kim,Dahl Park,Joohye Lee,Jayoung Lee,Hosang Jeon,Jiho Nam 대한방사선종양학회 2018 Radiation Oncology Journal Vol.36 No.2

Purpose: To evaluate the treatment outcomes of adjuvant external beam radiation therapy (EBRT) and vaginal brachytherapy (VB) following radical hysterectomy in cervical cancer patients with involved vaginal resection margin (VRM). Materials and Methods: We retrospectively reviewed the medical records of 21 patients treated with postoperative EBRT and VB for positive VRM FIGO stage IB–IIA cervical cancer between 2003 and 2015. Concurrent platinum-based chemotherapy was administered to all patients. Results: The median whole pelvis EBRT dose was 50.4 Gy (range, 45 to 50.4 Gy). In the VB, the median dose per fraction, number of fractions, and total dose delivered were: 4 Gy (range, 3.0 to 4.0 Gy), 4 fractions (range, 3 to 5 fractions), and 16 Gy (range, 12 to 20 Gy), respectively. At a median follow-up of 46 months (range, 9 to 122 months), local recurrence was observed in 2 patients, and distant metastasis was present in 7 patients. All patients with local recurrence subsequently developed distant metastases. The 5-year local control, disease-free survival, and overall survival rates were 89.1%, 65.9%, and 62.9%, respectively. Of the 21 patients, 7 patients (33.3%) reported grade 2 acute toxicity; however, there were no grade 3 or higher acute adverse events. Grade 1–2 late toxicities were observed in 8 patients. Late grade 3 urinary toxicity was reported in 1 patient. Conclusions: Adjuvant EBRT and VB showed excellent local control and low toxicity in cervical cancer patients with positive VRM. Although limited by its retrospective nature, the findings from our study provide evidence supporting the use of additional VB in pathologically involved VRM.

수직형 해수펌프 진동저감 사례 고찰

김원택(Wontaek Kim),김명천(Myongchon Kim),이혁순(Hyuksoon Lee) 한국소음진동공학회 2009 한국소음진동공학회 학술대회논문집 Vol.2009 No.11

Aluminum on steel preform closed-die forging manufacturing process for the production of automotive lightweight bearing hub

Dongwook Kim(김동욱),Wontaek Lee(이원택),Luca Quagliato,Seonggi Lee(이성기),Cheolsoo Lee(이철수),Naksoo Kim(김낙수) 한국자동차공학회 2017 한국자동차공학회 부문종합 학술대회 Vol.2017 No.5

수직 장축펌프 진동개선사례 고찰

김원택(Wontaek Kim),송우석(Woosok Song),장영기(Youngki Chang) 한국소음진동공학회 2011 한국소음진동공학회 학술대회논문집 Vol.2011 No.10

A deep-learning method using single phantom to enhance megavoltage image quality for patient positioning in chest radiotherapy: a feasibility study

Jeon Hosang,Kim Dong Woon,Joo Ji Hyeon,Ki Yongkan,Kim Wontaek,Park Dahl,Nam Jiho,Kim Dong Hyeon 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.1

Image-guided radiation treatment (IGRT) is essential for verifying patient positioning during modern radiotherapy. Although megavoltage digital radiographs (MV-DR) are available on most therapeutic linear accelerators and can be used for checking treatment beam shapes, they are much inferior to kilovoltage digital radiographs (KV-DR) in terms of image quality. As it is generally challenging to obtain a well-aligned MV−KV training dataset of patients in clinical scenarios, there is a lack of sufcient information on the accuracy of KV-DR synthesized using supervised training. Therefore, we aimed to synthesize pseudo KV-DR (pKV-DR) from MV-DR using a training dataset developed with a single anthropomorphic chest phantom. The phantom was adopted to obtain MV−KV image pairs at various gantry angles because these image pairs of patients are highly difcult to acquire and exactly align with each other. A deep-learning model based on U-net architecture was trained with the phantom image pairs using the mean absolute error (MAE) and structure similarity (SSIM) indices as loss functions. The mean MAEs of MV-DR and pKV-DR against KV-DR as the ground truth were 0.1152 and 0.0169, respectively, and their mean SSIM values were 0.9693 and 0.9942, respectively. Finally, pKV-DR showed a relatively high image similarity to that of KV-DR with smaller MAE (14.7%) and higher SSIM (2.5%), compared with MV-DR. The image contrast was also improved by 37.1% in clinical cases. The proposed method is expected to enable the implementation of improved IGRT with high image quality of KV-DR level, even in clinics where MV-DR is only available.