• Progress in Medical Physics
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• v.9 no.4
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• pp.267-276
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• 1998

Any detector inserted into a phantom should have such a geometry that it caused as small as possible perturbation of the electron fluence. Plane parallel chambers meet this requirement better than other chambers of configurations. IAEA protocol recommends the use of plane parallel chambers for this reason. However, the cylindrical chambers are widely used for convenient. The purpose of this study is to evaluate the absorbed dose due to the differences of four different dosimetry protocols such as IAEA protocol using cylindrical chamber, TG 21 protocol using cylindrical chamber, Markus protocol using plane parallel chamber, and TG 39 report for the calibration of plane parallel chamber in electron beams. Depth-ionization measurements for the electron beams of nominal energy 6, 9, 12, 15, and 18 MeV from Siemens accelerator with a 10$\times$10 cm$^2$ field size were made using a radiation field analyser with 0.125 cc ion chamber. Dosimetric measurements by IAEA and TG 21 protocol were made with a farmer type ionization chamber in solid water for each electron energy, respectively. Dosimetric measurements by Markus protocol were made with a plane parallel ionization chamber in solid water for each electron energy, respectively. The cavity-gas calibration factor for the plane parallel chamber was obtained with the use of 18 MeV electron beam as guided by TG 39 report. Dosimetric measurements by TG 39 were performed with a plane parallel ionization chamber in solid water for each electron energy, respectively. For all the energies and protocols, measurements were made along the central axis of the distance of 100 cm (SSD = 100 cm) with 10$\times$10 cm$^2$ field size at the depth of d$_{max}$ for each electron beam, respectively. In the case of 18 MeV, the discrepancy of 0.9 % between IAEA and TG 21 was found and the two protocols were agreed within 0.7 % for other energies. In the case of 18 MeV and 6 MeV, the discrepancies of $\pm$ 0.8 % between Markus and TG 39 was found, respectively and the two protocols were agreed within 0.5 % for other energies. Since the discrepancy of 1.6 % between cylindrical and plane parallel chamber was found for 18 MeV, it is suggested to get the calibration factor using other method as guided. by TG 39.9.

• 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.2 no.2
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• pp.155-160
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• 1991

We have studied the effective point of measurement for cylindrical ion chamber in water phantom for medical electron beams. Markus parallel plate chamber water phantom are used for the measurement of depth dose to determine the depth of the effective point of measurement for various energies(for electron 6MeV, 9MeV, 12MeV, 16MeV, and 20MeV; Co-60; for photon 6MV, 15MV). Cylindrical ion chambes(PTW233643 with r=2.75mm, PR-05P with r=2mm, and PM30 wiht r=15mm are used for the measurement of depth dose by same mtethod and the values of d$\_$50/ and R$\_$p/ obtained by three cylindrical chambers were compared with those of a flat chamber. From this we could evaluate the effective measuring points of cylindrical ion chamber. The effective point of measurement was estimated as 0.4～0.6r shifted toward surface from the center of the chamber for electron beam, 0.3～0.7r for $\^$60/Co X-ray.

• Progress in Medical Physics
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• v.7 no.2
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• pp.29-40
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• 1996

We had designed and made the cylindrical ionization chamber which operated above 5 mR/h. Using commercial electrometer, we investigated the characterictic of charge collection in the ion chamber. The active volume was 190.4㎤ and overall length and diameter in the chamber was 15.5cm, 5.22cm, respectively. The chamber had three electrodes(inner, central, wall electrode). And background current was 8.39${\times}$10$\^$-14/${\pm}$1.5${\times}$10$\^$-15/A to arrange the electrodes which were coaxial in chamber axis. The collection efficiency of chamber for Cs$\^$137/ was 99.7％ when the opreating voltage was applied 400V. Comparing with the commertial dosimetry system, the exposure calibration constant was 4.531${\times}$19$\^$7/R/C. By normalizing to CS$\_$137/ the relative energy response of the chamber was 1.30 for Am$\_$24/, 1.05 for C0$\_$60/, respectively. When the irrarition tranversed to the chamber axis, the isotropic effect of the chamber was not considerable.

• Nuclear Engineering and Technology
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• v.5 no.2
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• pp.94-102
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• 1973

Saturation characteristics of a current-type ionization chamber are investigated theoretically and experimentally in the columnar recombination region. The experiments were performed using a boron-lined cylindrical ionization chamber filled with nitrogen or helium at pressures of 760 mmHg and 380 mmHg. The collection efficiency deduced from the analytical method is in good agreement with the experimental results. This theory makes it possible to predict saturation characteristics for all ionization intensities with only the design data.

• Progress in Medical Physics
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• v.17 no.1
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• pp.54-60
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• 2006

In order to apply the TRS-398 dosimetry protocol developed by IAEA we directly calculated the quality correction factors for high energy photons. The calculations were peformed for seven commercial cylindrical chambers (A12, IC70, N23333, N30001, N30006, NE2571, PR06C/G). In comparison with quality correction factors given by TRS-398 our results were in good agreement within ${\pm}0.3%$ (maximum ${\pm}0.3%$) for all chambers and photon qualities.

• Progress in Medical Physics
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• v.20 no.1
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• pp.30-36
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• 2009

The quality correction in the air kerma dosimetry for Ir-192 using farmer type ionization chambers calibrated by Co-60 quality is required. In this study we determined quality factor ($k_u$) of two ionization chambers of PTW-N30001 and N23333 for Ir-192 source using dosimetric method. The quality factors for energy spectrum of microSelectron were determined as $k_u$=1.016 and 1.017 for PTW-N30001 and N23333 ionization chambers respectively. We applied quality factors in air kerma dosimetry for microSelectron source and compared with reference values. As a results we found that the differences between reference air kerma rate and measured it with and without quality correction were about -0.5% and -2.0% respectively.

• Journal of Radiation Protection and Research
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• v.16 no.2
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• pp.7-16
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• 1991

Measurement of Co-60 gamma rays has been made for establishment of exposure standard and analyze it's overall uncertainties. Exposure rate determined by the charge mode method using vibrating reed amplifier with cylinderical type cavity chamber. The values of a variety of physical constants and the correction factors are evaluated. The resulting exposure rate is 690.81 R/h at the distance of 1m from the source and the related uncertainties is ${\pm}0.8%$

• Radiation Oncology Journal
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• v.15 no.1
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• pp.65-69
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• 1997

Purpose : To obtain the actual dose distribution from measured data by doconvolution method using the measured ion chamber response function. Materials and Methods : The chamber response functions for 2 ionization chambers (diameter 5mm, 6.4mm) were measured. and dose Profiles were measured for $10{\times}20cm^2$ field size using two different detectors. The deconvolution of chamber response function from the measured data were performed for these Profiles. The same procedures were repeated for 4MV, 6MV and 1 SMV photon energies. Results : Different dose Profiles were obtained for the same field with the chambers which have the different response functions. Nearly the same results could be obtained with deconvolution for the profiles from various detectors. Conclusion : The effect of the chamber response function can be extracted by deconvolution method. Deconvolved dose profile using various ionization chambers gave better dose distributions. Technical improvements are needed for practical application.

• Progress in Medical Physics
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• v.16 no.2
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• pp.53-61
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• 2005

The quality factors for cylindrical ionization chambers for kV X-rays were determined by Monte Carlo calculation and measurement. In this study, the X-rays of 60-300 kV beam (lSO-4037) installed in KFDA and specified in energy spectra and beam qualities, and the chambers of PTW N23333 and N30001 were investigated. In calculations, the $R_{\mu}\;and\;R_{Q,Q_{0}}$ in IAEA dosimetry protocols were determined from the air kerma and the cavity dose obtained by theoretical and Monte Carlo calculations. It is shown that the N30001 chamber has a flat response of $\pm1.7\%$ in $110\~300kV$ region, while the response range of two chambers were shown to $\pm3\~4\%$ in $80\~250kV$ region. From this work we have discussed dosimetry protocol for the kV X-rays and we have found that the estimation of energy dependency is more important to apply dosimetry protocol for kV X-rays.