Hyong Geun Yun

Successful Treatment of Intractable Bleeding Caused by Radiation-Induced Hemorrhagic Gastritis Using Oral Prednisolone: A Case Report

Radiation-induced hemorrhagic gastritis is an intractable and dangerous condition. We describe a 59-year-old female patient with radiation-induced hemorrhagic gastritis. The patient underwent postoperative radiation therapy with a dose of 54 Gy in 30 fractions after a radical operation for a Klatskin tumor. Radiation volume included the gastric antrum. Approximately three months after radiation therapy, she was admitted for melena and anemia. Esophagogastroduodenoscopy showed an area of bleeding in the gastric antrum that was so diffuse that effective laser coagulation was not feasible. After failure of various treatments and transfusion of 7,040 mL of packed red blood cells, we successfully stopped the hemorrhage using oral prednisolone treatment. Based on this case, we think that oral prednisolone treatment can be tried as a first treatment for potentially life-threatening radiation-induced hemorrhagic gastritis.

An 87-year-old patient with repeated oligorecurrences over six years whose disease were treated with radiotherapy alone

In the clinical state of oligometastases or oligorecurrence, a transitional state between localized and widespread systemic disease, local control of the disease may yield improved systemic control. Radiotherapy may be a good means for controlling oligometastatic tumors, particularly in very old patients for whom surgery may be infeasible. A combination of systemic therapy and local therapy is necessary to prevent systemic progression. Some kinds of cancers found in the elderly are known to be somewhat indolent for systemic progression. So, for very old patients who refuse or cannot tolerate chemotherapy, the use of radical radiotherapy alone to treat oligorecurrences may be very helpful. We successfully treated an 87-year-old patient who had been diagnosed with oligorecurrences three times over six years with radiotherapy alone. The patient is now, about four years after his first radiotherapy for liver metastasis, alive without any evidence of cancer and with fully active performance status.

Design and Characteristics of Parallel Plate Type Ionization Chamber for the Measurement of High Energy Photon and Electron Beam

The dosimetric system consisting of parallel plate type of air-filled ionization chamber and charge to voltage converter was designed to do constancy check of the high energy photon and electron beam of clinical linear accelerator. The ionization chamber had been fabricated using an acrylic plate for the air cavity and two printed circuit boards for electrical configuration. The air gap between two electrodes ranged from 3 mm, 6 mm and 10 mm. The sensitive volume of the chambers were 0.9 cc, 1.9 cc and 3.1 cc respectively. The major parameters of the chamber characteristics such as zero drift current, leakage current, saturation voltage, reproducibility, linearity, EPM(Effective Point of Measurement), dose rate effect and polarity effect were measured. The experimental results are as followings. Zero drift currents were 0.23 pA for the volume of 0.9 cc, 1.9 cc and 0.45 pA for 3.1 cc. Leakage currents were 0.38 pAfor the volume of 0.9 cc, 1.9 cc and 0.56 pAfor 3.1 cc. Saturation voltages were 300 V, 400 V and 500 V for three kinds of chambers with volume of 0.9 cc, 1.9 cc and 3.1 cc respectively. Standard deviation of reproducibility was less than 0.003, and the linearity was measured within0.5% for all kinds of chambers. EPM(effective point of measurement) shifted towards the geometric center of the chamber as the plate separation increased. These data were comparable to those of commercially available dosimetric system for QA-purpose. This dosimetric system consisting of the ionization chamber, the PCB, and RF coaxial cables is satisfactory for the purpose of the constancy check of the high energy photon and electron beam from the medical linear accelerator.

A study on the characteristic of normoxic polymer gel dosimeter according to its composition

In this study, to find the optimal composition of the gel as therapeutic radiation, the amounts of methacrylic acid and gelatin were varied. The polymer gel with various compositions were evaluated for its sensitivity, reproducibility, and accuracy. As the concentration of the gelatine is high, the threshold R2 value increases and the dose response was decreases. As the concentration of the methacrylic acid is high, both the threshold R2 value and the dose response were decrease. As both concentrations of the gelatine and the methacrylic acid is high, the sensitivity to the dose was increases within some range. It was found that the polymer gel composed in this study can be optimized for measuring the therapeutic radiation.

Development of Transmission Dose Estimation Algorithm for in vivo Dosimetry in High Energy Radiation Treatment

In vivo dosimetry is very important for quality assurance purpose in high energy radiation treatment. Measurement of transmission dose is a new method of in vivo dosimetry which is noninvasive and easy for daily performance. This study is to develop a tumor dose estimation algorithm using measured transmission dose for open radiation field. For basic beam data, transmission dose was measured with various field size (FS) of square radiation field, phantom thickness (Tp), and phantom chamber distance (PCD) with a acrylic phantom for 6 MV and 10 MV X-ray. Source to chamber distance (SCD) was set to 150 cm. Measurement was conducted with a 0.6 cc Farmer type ion chamber. By using regression analysis of measured basic beam data, a transmission dose estimation algorithm was developed. Accuracy of the algorithm was tested with flat solid phantom with various thickness in various settings of rectangular fields and various PCD. In our developed algorithm, transmission dose was equated to quadratic function of log(A/P) (where A/P is area-perimeter ratio) and the coefficients of the quadratic functions were equated to tertiary functions of PCD. Our developed algorithm could estimate the radiation dose with the errors within ±0.5% for open square field, and with the errors within ±1.0% for open elongated radiation field. Developed algorithm could accurately estimate the transmission dose in open radiation fields with various treatment settings of high energy radiation treatment.