Su Chul Han

ASSESSMENT OF DIAGNOSTIC MULTILEAF COLLIMATOR FOR CEPHALOMETRIC EXPOSURE REDUCTION USING OPTICALLY STIMULATED LUMINESCENT DOSEMETERS

A diagnostic multileaf collimator (MLC) was developed for diagnostic radiography dose reduction. Optically stimulated luminescent dosemeters (OSLDs) were used to evaluate the efficacy of this device for dental radiography cephalometric exposure reduction. The OSLD dosimetric characteristics for 80 kVp cephalometric exposure were first obtained. The batch homogeneity and reproducibility were 1.67 % and 0.18-1.58, respectively. Good linearity was obtained between the OSLD dose and response, and the angular dependence was within ±4 %. The equivalent organ doses for the left eye, right eye and thyroid were 41.20±6.58, 178.86±1.71 and 171.12±8.78 μSv and 36.80±0.33, 156.63±0.22 and 22.04±0.13 μSv for the open and MLC fields, respectively. The MLC-induced dose reductions for the left and right eyes of in field were 10.67±16.78 and 12.42±8.84 %, respectively, and that of the thyroid gland of out of field was 87±8.82 %, considering combined uncertainty. Therefore, use of diagnostic MLC for dose reduction during dental radiography cephalometric exposure is both feasible and effective.

SU‐E‐T‐31: The Evaluation of Dosimetric Characteristics of OSLDs Based On Output Correction Factor in Low Energy

Purpose: The output of General X‐ray unit (low energy) has variation against 60Co unit. So it is necessary to minimize output variation when evaluating dosimetric characteristics of optical stimulated luminance dosimeters (OSLDs). Considering output variation of X‐ray unit, we evaluated dosimetric characteristics of OSLDs in low energyMethods: The OSLDs that used were nanoDotTM Dosimeter (Landauer Inc, Glenwood, USA) and this dosimeter had never been irradiated. Through single irradiate them (test dose was 7mGy), we certified batch homogeneity and sampled dosimeters with variation of radiation sensitivity within ± 1.5% among them. Using to these dosimeters certified reproducibility considering output variation every time when irradiated OSLDs. Through this process, we certified element correction factor (ECF) and coefficient of variation (COV) about each OSLD. Based on these OSLDs, we studied linearity, energy dependence and angular dependenceResults: The batch homogeneity was 1.21% of the coefficient of variation (after sampling). The average value of COV about reproducibility of OSLDs was reduced from 1.3% to 0.96% after applying to output correction factor. The linearity was that the correlation of between dose and count was fitted by linear function (R2 =0.997). The energy dependence study showed a range of ion chamber‐to OSLD rations from 0.23 (24.7 keV) to 0.27 (34.5 keV). According to energy, the range of angular dependence was from 0.1% to 8.4% variation when each degree was normalized by zero degreeConclusion: Considering output correction factor, reduced uncertainty occurred in general x‐ray unit. We acquired information that was ECF, COV of OSLDs in low energy. Using to these OLDs, It is feasible to measure patient dose of diagnostic radiography and Cone beam computed tomography for radiotherapy

COMPARISON OF SURFACE DOSES FROM INDIRECT AND DIRECT DIGITAL RADIOGRAPHY USING OPTICALLY STIMULATED LUMINESCENCE DOSEMETERS

An optically stimulated luminescence dosemeter was used to compare the surface dose to both eyes from an X-ray delivered frontally to the skull, and the dose could be reduced depending on image acquisition. The detectors were analysed in advance according to each image acquisition method, and the irradiation condition (mA) was obtained to equate the detective quantum efficiency of the two detectors. The surface doses to both eyes were measured in a human phantom. In the detector using the direct conversion method, the surface doses to both eyes were 0.29 ± 0.01 mSv (Rt. eye) and 0.28 ± 0.01 mSv (Lt. eye). In the detector using the indirect conversion method, the surface doses to both eyes were 0.23 ± 0.01 mSv (Rt. eye) and 0.23 ± 0.01 mSv (Lt. eye). Dose reduction by 18.00 ± 8.9% was permitted by the indirect method as compared with the direct method.

SU-F-I-78: Design of Diagnostic Multileaf Collimator Based On the Monte Carlo Simulation for Dose Reduction of Diagnostic Radiography

PURPOSE A diagnostics Multileaf Collimator (MLC) was designed for diagnostic radiography dose reduction. Monte Carlo simulation was used to evaluate efficiency of shielding material for producing leaves of Multileaf collimator. MATERIAL & METHODS The general radiography unit (Rex-650R, Listem, Korea) was modeling with Monte Carlo simulation (MCNPX, LANL, USA) and we used SRS-78 program to calculate the energy spectrum of tube voltage (80, 100, 120 kVp). The shielding materials was SKD 11 alloy tool steel that is composed of 1.6% carbon(C), 0.4% silicon (Si), 0.6% manganese (Mn), 5% chromium (Cr), 1% molybdenum (Mo), and vanadium (V). The density of it was 7.89 g/m3. We simulated leafs diagnostic MLC using SKD 11 with general radiography unit. We calculated efficiency of diagnostic MLC using tally6 card of MCNPX depending on energy. RESULTS The diagnostic MLC consisted of 25 individual metal shielding leaves on both sides, with dimensions of 10 × 0.5 × 0.5 cm3. The leaves of MLC were controlled by motors positioned on both sides of the MLC. According to energy (tube voltage), the shielding efficiency of MLC in Monte Carlo simulation was 99% (80 kVp), 96% (100 kVp) and 93% (120 kVp). CONCLUSION We certified efficiency of diagnostic MLC fabricated from SKD11 alloy tool steel. Based on the results, the diagnostic MLC was designed. We will make the diagnostic MLC for dose reduction of diagnostic radiography.

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-I-49: The Evaluation of Usability of Multileaf Collimator for Diagnostic Radiation in Cephalometric Exposure

PURPOSE This study evaluated usability of Multileaf collimator (MLC) for diagnostic radiation in cephalometric exposure using optical stimulated luminance dosimeters (OSLDs) METHODS: The MLC material was made alloy tool steel (SKD-11) and the density of it is 7.89g/m3 that is similar to it of steel (Fe, 7.85 g/m3) and the MLC was attached to general radiography unit (Rex-650R, Listem Inc, Korea) for cephalometric exposure. The OSLDs that used were nanoDotTM Dosimeter (Landauer Inc, Glenwood, USA) and we read out OSLDs with micro star system (Landauer Inc, Glenwood, USA). The Optical annealing system contained fluorescent lamps (Osram lumilux, 24 W, 280 ∼780 nm). To measure absorbed dose using OSLDs, was carried out dosimetric characteristics of OSLDs. Based on these, we evaluated dose reduction of critical organ (Eyes, Thyroids) with MLC in cephalometric exposure RESULTS: The dosimetric characteristics were following that batch homogeneity was 1.21% and reproducibility was 0.96% of the coefficient of variation The linearity was that the correlation of between dose and count was fitted by linear function (dose,mGy = 0.00029 × Count, R2 =0.997). The range of angular dependence was from -3.6% to 3.7% variation when each degree was normalized by zero degree. The organ dose of Rt. eye, Lt eye, thyroids were 77.8 μGy, 337.0 μGy, 323.1μGy, respectively in open field and the dose reduction of organ dose was 10.6%(8.3μGy), 12.4 %(42 μGy), 87.1%(281.4μGy) with MLC CONCLUSION: We certified dose reduction of organ dose in cephalometric exposure. The dose reduction of Eye was 11% because of reduction of field size and it of thyroids was 87% by primary beam shielding.

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‐711: Normal Tissue Tolerance Evaluation Tool for Clinical Protocols

Purpose: We developed Graphic User Interface (GUI) to evaluate and verify whether Dose Volume Histogram (DVH) parameters meet clinical protocol criteria. Methods: A graphical application to import and evaluate DVH parameters was developed by using Matlab (version R2012a, Mathworks). Two DVH text files which were exported from Eclipse treatment planning system (Varian, USA) could be imported, and it automatically depicts DVH values and arranges dose statistics in Eclipse manner (Figure 1). Additionally, it is possible to evaluate not only KIRAMS dose constraint protocol but also currently well‐known normal tissue constraint protocol such as American Association of Physicists in Medicine (AAPM), Radiation Therapy Oncology Group (RTOG) and Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC). Those protocols were able to be simultaneously depicted on the DVH so that dose constraints were easily distinguishable. Results: DVH data analyzed for all organ parameters with the application was faster than manually looking for points using the treatment planning system. Also, since a protocol‐specific marker used for evaluating dose constraint, the software was easily able to verify each depicted DVH for different types of patient plans whether under the protocol suggested dose or not (Figure 2). Conclusion: This software can help the planner to easily decide how much computer‐calculated DVH was over/under estimated on the basis of the dose constraints that clinical protocols suggested. Acknowledgement : This research was supported by the Ministry of education, Science and Technology(MEST)

SU‐E‐T‐38: The Evaluation of High Dose and Dosimetric Characteristics of Optical Stimulated Luminance Dosimeters in the 60CO Unit

Purpose: We aimed to evaluate optical stimulated luminance dosimeters (OSLD) to estimate high dose in 60Co unit and to compare to advanced study about OSLDMethods: OSLDs were grouped into three groups by radiation sensitivity (serial No.) and each groups consisted of dosimeters with variation of radiation sensitivity within ± 1.5% among them by sampling. When we evaluated dosimetric characteristics of OSLD, indicated used OSLD groups in list of evaluation of the dosimetric characteristics of them. OSLD had supra‐linear response from more than 3 Gy. So the correlation of between dose delivered from 60Co and count was fitted by quadratic function. We compared to calculation dose and delivery dose in more than 3 GyResults: The reproducibility was 0.76% of the coefficient of variation, the batch homogeneity was within 1.5 % of the coefficient of variation and the depletion by repeat reading was 0.04% per reading. The half time of count decay curve after irradiation according to reading time was 0.68 min. (1 Gy), 1.04 min. (5 Gy), and 1.10 min. (10 Gy), respectively and the count decay was stable after 11 min, After stability, coefficient of variation was within 0.4%.The removal rate of count by optical annealing time (30min.) after OSLD reading was 88% (1 Gy), 90% (5 Gy), and 92% (10 Gy), respectively and was 99% when they were annealed for 4hour. The diff. % of between delivery dose form 60Co unit and calculated dose from fitting model was within ± 4.0%. But the OSLDs irradiated dose above 20 Gy changed their radiation sensitivity. So it is necessary to use carefully them and to calibrate radiation sensitivity of themConclusion: Considering to uncertainty of count for procedure, if delivery dose was calculated, it is feasible to use OSLD for evaluation of high dose in 60Co unit. Acknowledgement:This research was supported by the Ministry of education, Science and Technology(MEST)