• Journal of radiological science and technology
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• v.35 no.3
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• pp.265-273
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• 2012

Aquisition of accurate beam data is very important to calculate a reliable dose distribution of the treatment planning system for small radiation fields in intensity-modulated radiation therapy(IMRT) and stereotactic radiosurgery(SRS). For the measurement of small fields, the choice of a suitable detector is important due to the shape gradient in profile penumbra, the lack of lateral electronic equilibrium, and the effect of effective detector volume. Therefore, this study was to analyze the dosimetric characteristics of various detectors in measurement of beam data for small fields of linear accelerator. 0.01cc and 0.13cc ion chambers (CC01 and CC13) and a stereotactic diode detector(SFD) were used for measurement of small fields. The beam data, including the percent depth dose, output factor, and beam profile were acquired under 6 MV and 15 MV photon beams. Measurements were performed with the field size ranging from $2{\times}2cm^2$ to $5{\times}5cm^2$. For $2{\times}2cm^2$ field size, the differences of the ratios of $PDD_{20}$ and $PDD_{10}$ measured by CC01 and SFD detectors were 1.02% and 0.12% for 6 MV and 15 MV photon beams, respectively. For field sizes larger than $3{\times}3cm^2$, the differences of values of $PDD_{20}/PDD_{10}$ obtained from each detector were 1.15% and 0.71% for 6 MV and 15 MV photon beams, respectively. The output factors obtained from CC01 and SFD for $2{\times}2cm^2$ field size were within 0.5% and 1.5% for 6 MV and 15 MV, respectively. The differences in output factor of three detectors for $3{\times}3cm^2$ to $5{\times}5cm^2$ field sizes were within 0.5%. Profile penumbras measured by the SFD, CC01, and CC13 detectors at three depths were average 2.7 mm and 3.5 mm, 3.4 mm and 4.3 mm, and 5.2 mm and 6.1 mm for 6 MV and 15 MV photon beams, respectively. In conclusion, it could be possible to use of the CC01 and SFD detectors for the measurement of percent depth dose and output factor for $2{\times}2cm^2$ field size, and to use of three detectors for $3{\times}3cm^2$ to $5{\times}5cm^2$ field sizes. CC01 and SFD detectors, consider ably smaller than the radiation field, should be used in order to accurately measure the profile penumbra for small field sizes.

• Radiation Oncology Journal
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• v.6 no.1
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• pp.101-108
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• 1988

The beam characteristics and dosimetric measurements of the 10MV X-ray beam from a Mevatron KD linear accelerator are examined. The Percent Depth Dose (POD) table and the Tissue Maximum Ratio (TMR) table are taken from measurement as a function of the field size and the depth. The calculated TMR table from PDD table is compared with those from measurement. Other beam characteristics such as output factor, beam profile (including flatness, symmetry and penumbra), wedge, and the variation of Dmax are presented.

• Progress in Medical Physics
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• v.14 no.4
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• pp.218-224
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• 2003

Purpose：By evaluating the dependence of the tray transmission factor (tray factor) on collimator setting and tray thickness, we determined the validity of the clinically used single tray factor for standard radiation field size (10${\times}$10 $\textrm{cm}^2$). Methods and Materials：For each X ray energies (6 and 10 MV), outputs were measured by using 5 steps of tray thickness (0, 6, 8, 10, 12 mm) and 7 steps of radiation field size (5${\times}$5, 10${\times}$10, 15${\times}$15, 20${\times}$20, 25${\times}$25, 30${\times}$30, 35${\times}$35 $\textrm{cm}^2$) at 10 cm phantom depth. Outputs were measured in both 'with tray' and 'without tray' conditions by using radiation with the same monitor units, and the tray factors were determined by the ratios of the two outputs. To evaluate the validity of a single tray factor obtained for standard radiation field, we analyzed the pattern of the field sizes in cases treated at our hospital in 2002. Results : In the 6 MV X-ray, the increases in the tray factor between the standard field (l0${\times}$10 $\textrm{cm}^2$) and the largest field (35${\times}$35 $\textrm{cm}^2$) were 0.517%, 0.835%, 1.058%, 1.066% in 6, 8, 10, and 12 mm thickness tray, respectively. In the 10 MV X-ray, the increases in the fray factor between the standard field (10${\times}$10 $\textrm{cm}^2$) and the largest field (35${\times}$35 $\textrm{cm}^2$) were 0.517%, 0.836%, 1.058%, 1.066% in 6, 8, 10, 12 mm thickness tray, respectively. In a major portion of clinical cases, when the field size was smaller than 20${\times}$20 $\textrm{cm}^2$, the tray factor was in good agreement with the standard tray factor. However, in cases where the field sizes were 30${\times}$30 $\textrm{cm}^2$ and 35${\times}$35 $\textrm{cm}^2$, the error could exceed 1.0%. Conclusion：The tray factor increased with increasing field size or decreasing tray thickness. The difference of tray factor between the small field and the large field increased with increasing tray thickness. Furthermore, the standard tray factor was valid in most clinical cases except for when the field size was greater than 30${\times}$30 $\textrm{cm}^2$, wherein the error could exceed 1.0%.

• Journal of Radiation Protection and Research
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• v.40 no.4
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• pp.211-215
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• 2015

In case of radiation emergencies, radioactive materials released into environments can cause internal exposure of members of the public. Even though whole body counters are widely used for direct measurement of internally deposited radionuclides, those are not likely to be used at the field to rapidly screen internal exposure. In this study, we estimated the counting efficiencies of portable NaI detector for different size BOMAB phantoms using Monte Carlo transport code to apply handheld gamma spectrometers for rapid screening of internal exposure following radiological accidents. As a result of comparison for two counting geometries, counting efficiencies for sitting model were about 1.1 times higher than those for standing model. We found, however, that differences of counting efficiencies according to different size are higher than those according to counting geometry. Therefore, we concluded that when we assess internal exposure of small size people compared to the reference male, the body size should be considered to estimate more accurate radioactivity in the human body because counting efficiencies of 4-year old BOMAB phantom were about 2.4~3.1 times higher than those of reference male BOMAB phantom.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.11
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• pp.1161-1169
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• 2003

In this paper, ADE(Axially Displaced Ellipse) Gregorian dual reflector antennas, which are the special form of Gregorian dual reflector antennas, were analyzed. In the procedure of antenna analysis, the aperture field distribution was obtained by using the geometrical optics and their far-field radiation characteristics were analyzed by using the aperture field method. The analysis results such as antenna efficiency, HPBW(Half Power Beam Width), FNBW(First Null Beam Width), and FSL(First Sidelobe Level) were presented as functions of edge taper and size of main reflector and subreflector. From the results in this paper, we could confirm that ADE reflector antennas have the different radiation characteristics from the classical dual reflector antennas.

• Nuclear Engineering and Technology
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• v.43 no.4
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• pp.399-404
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• 2011

A LEGO-type multi-purpose dosimetry phantom was developed for intensity-modulated radiation therapy (IMRT), which requires various types of challenging dosimetry. Polystyrene, polyethylene, polytetrafluoroethylene (PTFE), and polyurethane foam (PU-F) were selected to represent muscle, fat, bone, and lung tissue, respectively, after considering the relevant mass densities, elemental compositions, effective atomic numbers, and photon interaction coefficients. The phantom, which is composed of numerous small pieces that are similar to LEGO blocks, provides dose and dose distribution measurements in homogeneous and heterogeneous media. The phantom includes dosimeter holders for several types of dosimeters that are frequently used in IMRT dosimetry. An ion chamber and a diode detector were used to test dosimetry in heterogeneous media under radiation fields of various sizes. The data that were measured using these dosimeters were in disagreement when the field sizes were smaller than $1.5{\times}1.5\;cm^2$ for polystyrene and PTFE, or smaller than $3{\times}3\;cm^2$ for an air cavity. The discrepancy was as large as 41% for the air cavity when the field size was $0.7{\times}0.7\;cm^2$, highlighting one of the challenges of IMRT small field dosimetry. The LEGO-type phantom is also very useful for two-dimensional dosimetry analysis, which elucidates the electronic dis-equilibrium phenomena on or near the heterogeneity boundaries.

• Progress in Medical Physics
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• v.7 no.1
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• pp.9-17
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• 1996

The response function of ionization chambers are measured in the narrow radiation field Nominal photon energies are 4MV, 6MV and 15MV. the Radii of the chambers are 0.5cm～3.05cm and the field size is 0.2$\times$20$\textrm{cm}^2$. The measurements are taken in the water phantom at 10cm depth. The beam kernel (radiation distribution profile) for narrow radiation field in the phantom are obtained from Monte Carlo simulation (EGS4, Electron Gamma Shower 4). The beam kernel components in the measured chamber response function are deconvolved in order to get the ideal chamber response function of the $\delta$-shaped function radiation field. The chamber response functions have energy dependent tendency before deconvolution, while they show energy invariant properties, after the components of beam kernels are removed by deconvolution method.

• Progress in Medical Physics
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• v.1 no.1
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• pp.91-95
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• 1990

The solid state detector system was constructed using commercially available rectifier diode for the assessment of quality assurance in radiotherapy. Dosimetry system which consists of the electrometer and the water phanton was used for measuring small field size scanning. The measured results, which had linearity in accordance with variation of radiation dose for gamma-ray of Co- 60 and 6 and 10MV photons of linear accelerator, showed quite linear characteristics within 1% error. The percent depth dose of 10MV photon of Mevatron KD linear accelerator was measured in small field size using diode, and the results were compared with that of using ion chambers. The results show that the difference of percent depth dose between the value of diode and that of ion chamber was negligible in large field size. However, in small size less than 4$\times$4cm, the difference of percent depth dose estimated by diode and ion chamber was 4.7% by extrapolation to 0$\times$0cm. Considering the smaller volume of diode than that of ion chamber, it might be more reliable to use diode for estimating percent depth dose. Above results suggest that diode can be used for routine check such as beam profile, flatness, symmetry and energy

• Radiation Oncology Journal
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• v.11 no.2
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• pp.347-354
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• 1993

This is a retrospective analysis of 67 patients with histologically proven invasive carcinoma of uterine cervix treated with surgery followed by adjuvant radiotherapy at Inje University Seoul Paik Hospital between october 1983 and september 1991, Postoperative radiotherapy was carried out in patients with high risks of locoregional recurrence such as positive pelvic lymph node (38 pts), large tumor size more than 3 cm (22 pts), cervical stromal invasion more than 2/3 (46 pts), parametrial involvement (9 pts), positive resection margin (14 pts), endo/myometrial extension (10 pts), and angiolymphatic invasion (13 pts). Stage I A, I B, and IIA were 2 $(3\%),$ 39 $(58.2\%),\;and\;26\;(38.8\%),$ respectively. Median follow-up period was 48 months with ranges from 13 to 115 months. All 67 patients were treated externally with standard pelvic field with radiation dose ranging from 4080 to 6120 cGy in 4~6 weeks period of time. Of these, 45 patients received intracavitary radiotherapy. The overall survival rate and disease free survival rate at 5-year were $88.0\%\;and\;82.1\%,$ respectively. The survival rates by stage were $87.1\%$ in IB and $88.4\%$ in IIA. Local control rate was $80.6\%(58\;pts).$ The treatment failure was noted in 12 of 67 patients $(17.9\%):$ locoregional failure in $7(10.4\%),$ distant metastasis in 3 $(4.5\%),$ and locoregional and distant metastasis in $2(3\%),$ The univariate analysis of prognostic factors disclosed endo/myometrial extension as a significant factor of survival and recurrence $(70.0\%\;vs\;91.1\%\;P<0.05\;&\;30.0\%\;vs\;15.8\%,\;respectively).$ The complication of postoperative radiothrapy was not significant and all patient were well tolerated. In conclusion, postoperative radiotherapy in patients with high risks of locoreginal recurrence is relatively well tolerated and it gives significantly improved survival rate especially in patients with positive lymph nodes, bulky tumor size $(\geqq3\;cm),$ parametrial involvement, cervical stromal invasion more than 2/3, positive resection margin and angiolymphatic invasion.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.446-449
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• 2002

The video based electronic portal imaging device (EPID), which could display the portal image in near real time, was implemented to verify treatment position error in FSRT(Fractionated Stereotatic Radiation Therapy) instead of a portal film. Also, Developed FSRT system was composed of the stereotactic frame, frame mounting system and collimator cones. The verification of treatment position is very crucial in special therapies like FSRT. In general, the FSRT uses high dpse rate at small field size for treating small intracranial lesions. To evaluate quantitative positioning errors in FSRT, we used the first FSRT image as reference image and obtained the second FSRT image that was moved 2mm intentionally and detected intracranial contours after image processing. The generated 2mm error could be verified by overlapping only contours of two images. Through this study, the radiation treatment efficiency could be improved by performing precise radiation therapy with a developed video based EPID and FSRT.