Kum-Bae Kim

Long term follow-up results of external beam radiotherapy as primary treatment for retinoblastoma.

The authors reviewed their experiences of external beam radiotherapy (EBR) as an initial treatment in retinoblastoma patients to determine its long-term effect on subsequent tumor control and complications. A total of 32 eyes in 25 patients that underwent EBR for retinoblastoma were reviewed retrospectively. The patients consisted of 21 boys and 4 girls of median age at treatment of 7.1 months. Radiation doses ranged from 35 to 59.4 Gy. The 10-yr ocular and patient survivals were 75.4% and 92.3%, respectively. Nine of the 32 eyes progressed; 7 of these were enucleated and 2 were salvaged by focal treatment. According to the Reese-Ellsworth classification, 4 of 5 eyes of Group II, 13 of 16 Group III eyes, 2 of 4 Group IV eyes, and 5 of 7 Group V eyes were retained, and of the 32 eyes, 13 had visual acuity better than 20/200. Eleven patients experienced a radiation-induced complication. No patient developed a second malignancy during follow-up. Despite the limited number of patients enrolled, EBR may provide a mean of preserving eyeball and vision for some advanced lesions.

Stereotactic Body Radiotherapy for Oligometastases Confined to the Para-Aortic Region: Clinical Outcomes and the Significance of Radiotherapy Field and Dose

We retrospectively reviewed 88 patients with oligometases in the para-aortic region from any controlled primary tumor site who were treated with stereotactic body radiotherapy (SBRT). The 5-year local control, disease-free survival, and overall survival rates were 83%, 31%, and 41%, respectively. A 90% tumor-control probability was predicted at a biological effective dose of 90 Gy. Severe gastrointestinal toxicities (grade ≥3) were observed in 2 of 88 patients (1%). The results of this study are limited by the retrospective nature of the study but could serve as the background and rationale for future prospective trials on SBRT-based treatment for oligometastses.

SU-E-T-299: Dosimetric Characterization of Small Field in Small Animal Irradiator with Radiochromic Films

Purpose: The small animal irradiator has been used with small animals to optimize new radiation therapy as preclinical studies. The small animal was irradiated by whole- or partial-body exposure. In this study, the dosimetric characterizations of small animal irradiator were carried out in small field using Radiochromic films Material & Methods: The study was performed in commercial animal irradiator (XRAD-320, Precision x-ray Inc, North Brantford) with Radiochromic films (EBT2, Ashland Inc, Covington). The calibration curve was generated between delivery dose and optical density (red channel) and the films were scanned by and Epson 1000XL scanner (Epson America Inc., Long Beach, CA).We evaluated dosimetric characterization of irradiator using various filter supported by manufacturer in 260 kV. The various filters were F1 (2.0mm Aluminum (HVL = about 1.0mm Cu) and F2 (0.75mm Tin + 0.25mm Copper + 1.5mm Aluminum (HVL = about 3.7mm Cu). According to collimator size (3, 5, 7, 10 mm, we calculated percentage depth dose (PDD) and the surface –source distance(SSD) was 17.3 cm considering dose rate. Results: The films were irradiated in 260 kV, 10mA and we increased exposure time 5sec. intervals from 5sec. to 120sec. The calibration curve of films was fitted with cubic function. The correlation between optical density and dose was Y=0.1405 X3−2.916 X2+25.566 x+2.238 (R2=0.994). Based on the calibration curve, we calculated PDD in various filters depending on collimator size. When compared PDD of specific depth (3mm) considering animal size, the difference by collimator size was 4.50% in free filter and F1 was 1.53% and F2 was within 2.17%. Conclusion: We calculated PDD curve in small animal irradiator depending on the collimator size and the kind of filter using the radiochromic films. The various PDD curve was acquired and it was possible to irradiate various dose using these curve.

SU-E-T-315: The Change of Optically Stimulated Luminescent Dosimeters (OSLDs) Sensitivity by Accumulated Dose and High Dose

PURPOSE The objective of this study is to evaluate radiation sensitivity of optical stimulated luminance dosimeters (OSLDs) by accumulated dose and high dose. METHODS This study was carried out in Co-60 unit (Theratron 780, AECL, and Canada) and used InLight MicroStar reader (Landauer, Inc., Glenwood, IL) for reading. We annealed for 30 min using optical annealing system which contained fluorescent lamps (Osram lumilux, 24 W, 280 ∼780 nm). To evaluate change of OSLDs sensitivity by repeated irradiation, the dosimeters were repeatedly irradiated with 1 Gy. And whenever a repeated irradiation, we evaluated OSLDs sensitivity. To evaluate OSLDs sensitivity after accumulated dose with 5 Gy, We irradiated dose accumulatively (from 1 Gy to 5 Gy) without annealing. And OSLDs was also irradiated with 15, 20, 30 Gy to certify change of OSLDs sensitivity after high dose irradiation. After annealing them, they were irradiated with 1Gy, repeatedly. RESULTS The OSLDs sensitivity increased up to 3% during irradiating seven times and decreased continuously above 8 times. That dropped by about 0.35 Gy per an irradiation. Finally, after 30 times irradiation, OSLDs sensitivity decreased by about 7%. For accumulated dose from 1 Gy to 5 Gy, OSLDs sensitivity about 1 Gy increased until 4.4% after second times accumulated dose compared with before that. OSLDs sensitivity about 1 Gy decreased by 1.6% in five times irradiation. When OSLDs were irradiated ten times with 1Gy after irradiating high dose (10, 15, 20 Gy), OSLDs sensitivity decreased until 6%, 9%, 12% compared with it before high dose irradiation, respectively. CONCLUSION This study certified OSLDs sensitivity by accumulated dose and high dose. When irradiated with 1Gy, repeatedly, OSLDs sensitivity decreased linearly and the reduction rate of OSLDs sensitivity after high dose irradiation had dependence on irradiated dose.

SU‐E‐T‐268: The Evaluation of Dosimetric Characteristic of Radiophotoluminescent Glass Dosimeter According to Reading Methods of Reader

Purpose: Statistical checks of system parameters and follow up of readers behavior will give a broader understanding into the operational characteristics of the reader and may help for proper maintenance of the system. The purpose of this study is to suggest effective use of reading methods for reducing the uncertainty in dose measurements through the investigation of characteristics of GD‐based reader system. Methods: To evaluate the characteristics of readers, we performed measurement such as reproducibility of repeated reading, readout variation according to the number of GD loading on readout magazine, and deviation depending on each magazine position. To evaluate dose reproducibility we made a try to do repeated reading up to 200 times for each 15 GDs. Also, to evaluate readout variation characteristic, 80 GDs are irradiated one by one under the same irradiation conditions. Reading process was measured with 4 different cases. Lastly, to measure the deviation magazine position, we examine the readout values according to each loading position.Results: According to measurement result, reproducibility shows 1.3% lower measurement from total 200 times. Readout sensitivity of GD on magazine values is normalized to 1st position response. 1 to 5th position measured 1.015, also 1 to 10th position examined 1.022, and 1 to 20th position presented 1.035. Lastly, at all position except for 20th position of magazine, response is tend to increase gradually. It was overestimated on 2.0% of average rather than response at reference position (first position). Conclusions: According to the result, we should put each GD in consecutive order from 1st space of magazine to get accuracy value of dose and it is recommended that reading process should be performed the only first position of magazine with regard to absolute dosimetry. This work was supported by Nuclear Research & Development Program of the National Research Foundation of Korea(NRF) grant funded by the Korean government(MEST).

The Development of a Mid-Dose Irradiator for Radiation Biology Study

Recent we developed a mid-dose irradiator at KIRAMS using Cesium-137 sources for studies of mid-dose radiation effects in biology and also for a calibration of Thermo Luminescent dosimeter (TLD). In this paper, we will introduce the design, construction and performance test of the convenient mid-dose irradiator. The source housing of the irradiator contained three rods sources, which were separated by 10 cm in order to produce a uniform dose distribution. When operating to exposure the radiation to the biological samples, the source housing will rotate 180 degrees and face to biological samples, or TLD. After irradiating for the set time, it will return to its shielded position. A compact Field Point (CFP) controls the sequence of operation, interlock, motor rotation and safety system. The rotation speed of biological samples can vary up to 20 RPM. A real time monitoring system was also incorporated to check and control the operation status of the irradiator. The capacity of the irradiation chamber was 5 liters. The isodose distribution at arbitrary vertical plans was measured by using film dosimetry. The dose-rate was determined 1.25 cGy/min in air equivalent material in the case of 55.5GBq Cesium-137. The homogeneity of dose distribution in the chamber was ±10%. The radiation level with a maximum 3 µSv/hr radiation leakage measured on its surface was considered within permissible levels for the operation.