Hideki Aoyama

Okayama University, Okayama, Okayama, Japan

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Publications (6)1.45 Total impact

  • Hideki Aoyama, Yoshiharu Azuma, Keiji Inamura
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    ABSTRACT: The purpose of this study is to quantify the magnitudes of the position shifts of internal structures together with the correlation between the day-to-day positioning of the prostate and the bony anatomy using an integrated CT-linear accelerator system for external beam radiation therapy for prostate cancer. A total of 1176 pretreatment in-room CT images and their digitally reconstructed radio-graph (DRR) pairs from 33 patients were acquired over the course of the study. The differences between the isocenter of the prostate on in-room CT and the isocenter of the bony anatomy on DRR were analyzed. The agreement between positions in each direction was compared using Bland-Altman limits of agreement. The 95% limits of agreement in lateral (LR), superoinferior (SI), and anteroposterior (AP) directions were -2.98 to 2.49 mm, -4.69 to 5.75 mm, and -8.23 to 7.30 mm, respectively. The isocenter was localized to within 3.0 mm on in-room CT images and DRR 99.0% in LR, 85.1% in SI, and 85.9% in AP. Considerable differences between in-room CT images and DRR exist. These data demonstrate that there is a significantly greater shift in the SI and AP directions than in the lateral direction for the entire patient group. Applications such as our image guide system will, with routine clinical use, continue to improve the precision of external beam radiation therapy for prostate cancer.
    Journal of Radiation Research 01/2011; 52(2):220-8. · 1.45 Impact Factor
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    ABSTRACT: The objective of this study was to extend the usable dose measurement range of Gafchromic EBT film (EBT). EBT has the advantages of high sensitivity and improved film uniformity up to 8.0 Gy over Gafchromic MD-V2-55 film (MD-V2-55). EBT samples were exposed from 0.3 to 80 Gy. Optical densities of the samples were measured using ES-2200 (Seiko Epson Corporation, Nagano, Japan). EBT has an absorption spectrum with a maximum absorption band centered at 630 nm. The wavelength position of a maximum absorption does not shift with increasing dose within usable dose range. High sensitivity measurement of density can be performed using measurement light of 630 nm. We designed a flat-bed document scanner with single emission spectrum centered at 630 nm (IR-4000, iMeasure, Inc.) for EBT. Optical densities of the samples were also measured using IR-4000. The optical density response characteristics obtained by the combinations of EBT/ES-2200 and EBT/IR-4000 were compared with those of MD-V2-55/ES-2200. As a result, optical densities of EBT increased from 8.0 to 80 Gy. From the optical densities the calibration curves of net optical density versus delivered dose for dosimetry could be obtained. The combinations of EBT/ES- 2200 and EBT/IR-4000 had higher sensitivity of densitometry than MD-V2-55/ES-2200. The sensitivity of EBT/IR-4000 was highest. rror of dose measurements up to 80 Gy is within about ±5%, ±8%, and ±4% for MD-V2-55/ES-2200, EBT/ES- 2200, and EBT/IR-4000, respectively. The IR-4000 with single emission spectrum can bring out the capacity of high sensitivity and accuracy of EBT up to 80 Gy. Keywordsextension-dose measurement range-Gafchromic EBT film-flat-bed document scanner-Gafchromic MD-V2-55 film
    12/2009: pages 200-203;
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    ABSTRACT: Purpose: We developed an infrared flat-bed scanner with a transparency unit (IR 4000, iMeasure, Inc.) in order to increase the sensitivity of measuring density of Gafchromic EBT film (International Specialty Products). Then, the performance of IR 4000 was investigated, comparing with a general-purpose flat-bed scanner. Methods and Materials: Gafchromic EBT film (EBT) has the absorption spectrum with a maximum absorption band centered at 636 nm. Consequently the response of EBT will be enhanced by measurement with red light. Then, the transparency unit of IR 4000 for EBT has light emitting diode (LED) with a peak wavelength of 630 nm, and was produced by replacing LEDs of white light in the transparency unit for the flat-bed scanner (ES 2200, Seiko Epson Corp). Samples of EBT were covered with solid water RMI-457 phantoms and were exposed to the following doses: 0.3 – 10.0 Gy with the 6 MV photon beam from a Siemens MEVATRON77 DX67 accelerator. The irradiated samples were scanned by IR 4000 with 48 bit color mode and 1200 dpi and the scan data of red channel was converted into optical density. And also, the samples to which the yellow filter (International Specialty Products) was added were scanned by ES 2200. Furthermore the optical density by the two scanners was divided by the absorbed dose and the value was estimated as sensitivity. Result and Discussion: EBT using IR 4000 was about 1.60 times more sensitive on the average than using ES 2200 with the yellow filter in the dose range from 0.3 Gy to 10.0 Gy. By using IR 4000, the increase of sensitivity for EBT is easily achieved without using the filter which has the problem of dust, scratch or oxidation. Conclusion: The high capability of all Gafchromic films is utilizable by employing IR 4000 which has the easily exchangeable transparency unit.
    12/2006: pages 2163-2167;
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    ABSTRACT: To increase the sensitivity of the dosimetry system for high energy x-rays, using Gafchromic EBT film (International Specialty Products) and a flat-bed scanner with transparency unit (ES-2200 or Expression 1680, Epson, Inc.), the optimal sharp cut (SC) filters like optical filters to be added to the scanner were investigated. Gafchromic EBT film (EBT) has the absorption spectrum with a maximum absorption band centered at 636 nm. Consequently the response of EBT will be enhanced by measurement with red light and can be very significantly increased by using a red filter while making scanner measurements. In our research, employed SC filters were SC filter 54, 56, 58, 60 and 62 (product made from Fuji film). SC filters are defined as filters that cut off as much as possible of the wavelength light shorter than a specific wavelength, while transmitting as much of longer wavelength light as possible, within a wavelength range of 350 nm to 800 nm. Generally, it is ideal to use a narrow band pass filter. However we didn’t employ the filter because the transmissivity of the filter of film type is low or the thickness of glass type filter is large, so it is unsuitable for a flat-bed scanner. Film pieces of EBT were exposed to the following doses: 0.3 – 10.0 Gy with the 6 MV x-rays from a linear accelerator. The irradiated film pieces to which the SC filter was added were scanned and the scan data of red channel was converted into optical density. Furthermore the optical density was divided by the absorbed dose and the value was estimated as sensitivity. EBT with SC filter 62 with 50% of transmissivity at 620 nm was about 1.48 times more sensitive on the average than without a SC filter.
    12/2006: pages 2138-2141;
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    ABSTRACT: Radiochromic film (RCF) has been applied to mapping of dose distributions in radiation therapy. However, this particular RCF product suffers from intrinsic nonuniform response. In this study, we have carefully measured the nonuniformity of unirradiated RCF, and the response of irradiated RCF in pixel-to-pixel as function of various absorbed doses, in order to ascertains for the method of predicting the error of irradiated, unirradiated RCF
    Instrumentation and Measurement Technology Conference, 2006. IMTC 2006. Proceedings of the IEEE; 05/2006
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    ABSTRACT: Radiochromic film (RC-film) is of great interest as a film-type dosimeter for radiation oncology applications. We present a two-dimensional image-based evaluation of the measurement accuracy of a commercial RC-film product (Gafchromic MD-55-2 film, ISP TECHNOLOGIES, Inc.) by using a commercial Laser Densitometer (Model 1710, Computerized Medical Systems, Inc.) as an optical density imaging system. The coefficient of variation of the density (pixel-value) in one sample was approximately 3% to 11% at 3 Gy or less, and 3% or less at 4 to 60 Gy. Although the coefficient of variation between three samples at the same dose was about 14% at 1 Gy, it decreased as the dose increased, reaching several percent. In 1 to 6 Gy samples, geometric imaging artifacts [interference (moire) patterns] were observed, and it was found that scan-sampling pitch influenced the accuracy of measurement of the density of the sample. To improve the accuracy of density measurement, sufficient knowledge about characteristic features of the density measuring system is essential.
    Nippon Hoshasen Gijutsu Gakkai zasshi 12/2004; 60(11):1533-42.