Dong Oh Shin

Dose response of commercially available optically stimulated luminescent detector, AL2O3:C for megavoltage photons and electrons

This study examined the dose response of an optically stimulated luminescence dosemeter (OSLD) to megavoltage photon and electron beams. A nanoDot™ dosemeter was used to measure the dose response of the OSLD. Photons of 6-15 MV and electrons of 9-20 MeV were delivered by a Varian 21iX machine (Varian Medical System, Inc. Milpitas, CA, USA). The energy dependency was <1 %. For the 6-MV photons, the dose was linear until 200 cGy. The superficial dose measurements revealed photon irradiation to have an angular dependency. The nanoDot™ dosemeter has potential use as an in vivo dosimetric tool that is independent of the energy, has dose linearity and a rapid response compared with normal in vivo dosimetric tools, such as thermoluminescence detectors. However, the OSLD must be treated very carefully due to the high angular dependency of the photon beam.

Secondary neutron dose measurement for proton eye treatment using an eye snout with a borated neutron absorber

BackgroundWe measured and assessed ways to reduce the secondary neutron dose from a system for proton eye treatment.MethodsProton beams of 60.30 MeV were delivered through an eye-treatment snout in passive scattering mode. Allyl diglycol carbonate (CR-39) etch detectors were used to measure the neutron dose in the external field at 0.00, 1.64, and 6.00 cm depths in a water phantom. Secondary neutron doses were measured and compared between those with and without a high-hydrogen–boron-containing block. In addition, the neutron energy and vertices distribution were obtained by using a Geant4 Monte Carlo simulation.ResultsThe ratio of the maximum neutron dose equivalent to the proton absorbed dose (H(10)/D) at 2.00 cm from the beam field edge was 8.79 ± 1.28 mSv/Gy. The ratio of the neutron dose equivalent to the proton absorbed dose with and without a high hydrogen-boron containing block was 0.63 ± 0.06 to 1.15 ± 0.13 mSv/Gy at 2.00 cm from the edge of the field at depths of 0.00, 1.64, and 6.00 cm.ConclusionsWe found that the out-of-field secondary neutron dose in proton eye treatment with an eye snout is relatively small, and it can be further reduced by installing a borated neutron absorbing material.

Evaluation of the Accuracy of the CyberKnife

The use of stereotactic radiosurgical systems to treat intracranial and extracranial tumors and other lesions requires a high degree of accuracy in target identification and localization. CyberKnife can deliver, with a high degree of precision, a single or several fractions of radiation dose to a well-defined small intracranial or extracranial target. The accuracy of the output factor directly affects the accuracy of dose delivery in CyberKnife system. The purpose of this study was to evaluation the total system accuracy of the CyberKnife and also to estimate an output factor for CyberKnife using the several detectors. Accuracy of target localization was measured in anthropomorphic head phantom containing a spherical target, fiducial markers, and two pieces of film. The accuracy measured is the displacement of the dose contours from the treatment plan to that measured in the exposed phantom. All measurements of the output factors for collimators were performed by six different detectors: diode detector, X-Omat V film, Gafchromic EBT film, 0.015, 0.125 and 0.6 cc ionization chamber. Each collimator normalized with respect to the output factor of the largest collimator. We performed the E2E test and the general film dosimetry for estimation target localization in CyberKnife. The targeting error of the skull tracking mode and fiducial tracking mode were 0.956 mm and 0.923 mm. We could confirm the accuracy of total system is less than the 1 mm. For larger collimators, the output factors from six detectors showed a good agreement. For the collimators less than 15 mm, there were substantial differences in the output factors among different detectors. That is, the value of output factor for the 5 mm collimator of a diode and Gafchromic film was each 0.656 and 0.777. The Gafchromic EBT film was considered more accurate than the others detectors.

Adenovirus-mediated Foxp3 expression in lung epithelial cells ameliorates acute radiation-induced pneumonitis in mice.

Forkhead transcription factor 3 (Foxp3) has a critical role in regulatory T cells (Treg). There are an increasing number of researches concerning the functions of Foxp3 in other cells, including lung epithelial cells besides Treg. However, the roles of Foxp3 in lung epithelial cells remain poorly understood. To examine the potential therapeutic benefits of Foxp3 for lung inflammation, this study investigates the effect of adenovirus-mediated Foxp3 overexpression in a radiation-induced lung damage model. Foxp3-EGFP expressing adenovirus was administered by intratracheal injection three times over 14 days after focal X-ray irradiation. To evaluate effects of Foxp3 overexpression in radiation-induced lung inflammation, immune cell profiles of bronchoalveolar lavage (BAL) fluid were analyzed. Foxp3 gene-delivered mice showed significant inhibition of immune cell infiltration, such as eosinophils, lymphocytes, macrophages and neutrophils in BAL fluid. Histopathological analysis also showed that Foxp3 overexpression inhibits inflammatory cell recruitment and collagen deposition in lung tissues. In addition, expression of inflammatory and fibrosis-related genes was decreased in the Foxp3 expression adenovirus-infected group. These results suggest that Foxp3 expression in lungs holds considerable therapeutic potential for attenuating inflammation and fibrosis in radiation-induced lung injury.

Status and Perception of Risk Management in Radiation Therapy: Survey Among Korean Medical Physicists

Abstract This study was conducted as part of an endeavor to improve the risk management system of radiation therapy departments in the Republic of Korea. An online survey on the status and perception of Korea’s medical physicists on risk management in radiation therapy was carried out. A total of 40 domestic radiation oncology departments participated. This survey is divided into three categories: (1) work environment; (2) risk management status; and (3) opinions on how to improve risk management. Based on the results of the survey, the conclusions that can be derived are (1) the majority of respondents have a high interest in the risk management of radiation therapy; (2) the lack of staffing is one cause of risk management difficulties; (3) a risk-related terminology and classification system at the national or professional association level are required; (4) each hospital should create a voluntary reporting system for the handling of incidents; (5) medical physicists should establish incident reporting, analysis and countermeasures; and (6) government should develop education and training programs. It was confirmed that the current risk management system should be changed by education in the hospital and at the national level in order to improve risk management related to radiation therapy. In addition, it was recognized that a dedicated staff and a risk management certification system and organization for patient safety in radiotherapy are needed.

SU‐E‐T‐36: Determination of the Beam Quality Correction Factor for the Liquid Ioinization Chamber in a Clinical Photon Beam

Purpose: The beam quality correction factor Koo0 of microLion chamber is still unknown and should be determined for the application of the chamber to the reference dosimetry. The objective of this study is to calculate the beam quality correction factor of microLion chamber for the high energy 6MV photon beam from Clinac iX (Varian, USA) using two alternative ways; Monte Carlo simulation, in particular EGSnrc system and experimental decision. Methods: For the present work the Cobalt60 gamma beam (Theratron780) is employed as beam source in the calibration beam quality and the high energy 6MV photon beam from the Linac (Clinac iX) is selected as quality of user beam. We have employed the egs cavity code, the EGSnrc user code, to model microLion chamber. Results: The correction factor of the PTW30013 chamber is given 0.995 for the photon beam quality TPR20,10 of 0.663. We get the Result of 1.024(±0.58%) for the TPR20,10 factor of the microLion chamber for the 6MV photon beam with its beam quality TPR20,10 of 0.663 using Monte Carlo simulation. The correction factor is calculated for the microLion chamber and for the 6MV photon beam with its beam quality of 0.665 is and shows good agreements within 0.56% with the one measured (1.024). Conclusion: The beam quality correction factor of the microLion chamber was determined with its correction factor unknown for the 6MV photon. The results from two methods were in good agreements within acceptable uncertainties. There remains a problem that uncertainties associated with microLion chamber should be studied further, but we think the averaged factor 1.0212 could be used for the microLion chamber and for the same photon beam quality as in this study in the reference dosimetry.

The Feasibility of Goggle Monitor for Respiratory Biofeedback of Patient to Reduce Correlation Error Using Real-Time Tumor Tracking System

The aim of this study was to reduce correlation error using goggle monitor during treatment radisurgery using CyberKnife system. We analyzed the correlation error during treatment radiosurgery without goggle monitor and with using goggle monitor. The correlation error for free breathing was form 0.215 mm to 9. Oil mm. However, using goggle monitor is from 0.239 mm to 8.376 mm. We commended to use goggle monitor which can biofeedback her respiratory cycle and shape to reduced correlation error during treatment radiosurgery

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.

Calibration of Ir-192 HDR Source based on Standards of Absorbed Dose toWater

Brachytherapy sources are usually calibrated in terms of the measured air-kerma strength SK in free space at 1 m distance. The trend of the protocols for the external beam radiotherapy has been changing from an air_kerma base to standards of absorbed dose to water. In this work we tried to specify the source strength of Ir-192 source in terms of the absorbed_dose_to_water instead of an air kerma strength using standards of absorbed dose to water.