Hideki Aoyama

Okayama University, Okayama, Okayama, Japan

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Publications (16)6.46 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.
    No preview · Article · Jan 2011 · Journal of Radiation Research
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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
    No preview · Chapter · Dec 2009
  • Yoshiharu Azuma · Hideki Aoyama · Sachiko Goto
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    ABSTRACT: We developed an infrared flat-bed scanner with a transparency unit (IR-4000, iMeasure, Inc.) in order to increase the sensitivity of the measuring density of Radiochromic film , Gafchromic film EBT model. Radiochromic film has been used for many years as a two-dimensional radiation detector for dosimetry in radiotherapy. One of the commercially available Radiochromic films today is the Gafchromic film EBT model (EBT) manufactured by ISP (International Speciality Products, Wayne, NJ). EBT has the absorption spectrum with a maximum absorption band centered at 636 nm. Consequently the response of EBT will be enhanced by measuring with a red light. The transparency unit of IR-4000 for EBT has a light emitting diode (LED) with apeak wavelength of 630 nm, and was produced by replacing a white light in the transparency unit for the flat-bed scanner (ES-2200, Seiko Epson Corp) with the LEDs. IR-4000 could improve the sensitivity for EBT in all dose ranges. However, we had to consider the methods for decreasing noise. We examined for IR-4000 how to keep the high sensitivity and reduce noise. Multiple scans and the reduction of the image resolution by pixel averaging, which was effective in noise reduction, were employed. IR-4000 is a useful densitometry device to GAFs since optional transparency units which have various single emission spectra are prepared.
    No preview · Conference Paper · Jun 2008
  • Hideki Aoyama · Yoshiharu Azuma · Sachiko Goto
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    ABSTRACT: PURPOSE Radiochromic films (RCFs) has been used for many years as a two-dimensional radiation detector for dosimetry in radiotherapy. In the past few years, two new RCFs, HS and EBT models, have been introduced in clinical use. We developed an infrared flat-bed scanner (Model: IR-4000) with two types of interchangeable transparency units in order to improve the sensitivity of the densitometry of two RCF models. The monochromatic luminescence spectrum densitometry for RCF is accomplished with the aid of a novel infrared flat-bed scanner. The purpose of this study was to investigate the densitometry properties of the RCFs in combination with infrared flat-bed scanner. METHOD AND MATERIALS The maximum absorption peak for the HS model is centered at 673 nm, while the EBT model is centered at 633 nm. The IR-4000 has been developed with regard to absorption peak properties of the RCFs. The single-peak wavelength of each transparency unit is 630 nm and 670 nm. These transparency unit replacements are extremely easy and can be performed in field. Samples of RCF were covered with solid water RMI-457 phantoms and were exposed to the following doses: 0.3 - 50 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 was converted into optical density. The optical density by the IR-4000 was divided by the absorbed dose and the value was estimated as sensitivity. RESULTS The IR-4000 is approximately 1.60 times more sensitive than the general-purpose flat-bed scanner in all dose range for HS and EBT models. When using the broadband emission light source of the general-purpose flat-bed scanner, even if only the red component is extracted, a different sensitivity is obtained when compared to the monochromatic luminescence spectrum of IR-4000. CONCLUSION Our novel infrared flat-bed scanner will further improve the accuracy of the densitometry. We suggest that the IR-4000 is suitable device for analyzing RCFs. CLINICAL RELEVANCE/APPLICATION The IR-4000 provides a platform for further studies in high resolution film dosimetry where steep dose gradients are present such as IMRT, stereotactic radiotherapy and intravascular brachytherapy.
    No preview · Conference Paper · Nov 2007
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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.
    No preview · Chapter · Dec 2006
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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.
    No preview · Chapter · Dec 2006
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    ABSTRACT: Radiochromic film 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 create a method of predicting the error of irradiated, unirradiated RCF.
    No preview · Conference Paper · Nov 2006
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    ABSTRACT: We built an estimation system of individual breast density from digital mammograms by using breast tissue equivalent phantoms that are able to change the mixture ratio of adipose and glandular tissue and the thickness. The method was compared with a visual assessment of breast density by the radiologists as a gold standard. The clinical image data set average of the estimated glandular rate was 35.0%, while varying from 12.0% to 67.0%. This system can apply in clinical practice such as the visual estimation of breast density.
    No preview · Conference Paper · Nov 2006
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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
    No preview · Conference Paper · May 2006
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    ABSTRACT: LEARNING OBJECTIVES We restrict our investigation to clinical dosimetry, which we define over the range 0-60 Gy. (1)Characteristics of available radiochromic films. (2)Characteristics of scanning systems and densitometers. The results presented in this study would serve as guidelines for the GafChromic film dosimetry system characteristics. ABSTRACT Radiochromic film (RC-film) is of great interest as a film type dosimeter for radiation oncology applications. We present two-dimensional image-based evaluation of measurement accuracy of a commercial RC-film product (Gafchromic MD-55-2 film) density by using a commercial Model 1710 Laser Densitometer as an optical density imaging system. The coefficient of variation of the density (pixel value) in one sample was about 3 to 11% in 3 Gy or less, and was 3% or less in 4 to 60 Gy. Although the coefficient of variation between 3 samples in the same dose was about 14% in 1Gy, it decreased as the dose increased and became several percent. In 1 to 6 Gy samples, geometry imaging artifacts [interference (moire) patterns] were observed and it turned out that scan-sampling pitch influenced measurement accuracy of density of the sample. For improvement in accuracy of density measurement, sufficient knowledge about characteristic feature of density measuring system is essential.
    No preview · Conference Paper · Nov 2005
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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.
    No preview · Article · Dec 2004 · Nippon Hoshasen Gijutsu Gakkai zasshi
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    ABSTRACT: Purpose: A linear accelerator (linac) takes a leading role in radiation therapy. A linac consists of complicated main parts and systems and it is required that highly accurate operational procedures should be maintained. Operational failure occurs for various reasons. In this report, the failure occurrences of one linac over a ten year period were recorded and analyzed. Materials and Methods: The subject model was a MEVATRON77 DX67 (Siemens, Inc). The failure rate for each system, the form classification of the contents of failure, the operation situation at the time of failure, and the average performance life of the main parts were totaled. Moreover, the relation between the number of therapies that patients received (operating efficiency) and the failure rate within that number and the relation between environment (temperature and humidity) and the failure rate attributed to other systems were analyzed. In this report, irradiation interruption was also included with situations where treatment was unable to begin in total for the number of failure cases. Results: The cases of failure were classified into three kinds, (A): irradiation possible, (B): irradiation capacity decreased, and (C): irradiation impossible. Consequently, the total failure number of cases for ten years and eight months was 1,036, and the number of cases/rate of each kind were (A): 49/4.7%, (B): 919/88.7%, and (C): 68/6.6%. In the classification according to the system, the acceleration section accounted for 59.0% and the pulse section 23.2% of the total number of failure cases. Every year, an operating efficiency of 95% or higher was maintained. The average lives of a thyratron, a klystron, and RF driver were 4,886 hours, 17,383 hours, and 5,924 hours respectively. Moreover, although analysis of the relation between the number of therapies performed (or operating time) and the number of failures for each main machine part was observed, the tendency was not to associate them with each other. The relation between environment and the number of failures, it was observed that in the acceleration and pulse sections, failures increased as climatic temperatures fell. Conclusions: It is necessary to record equipment problems and failure in detail over a long period of time, to perform complete analyses, and to have a good working knowledge of equipment functions. Moreover, it is important to attempt to forecast future failures from observed failure patterns and, if possible, to avoid total failure in advance with prompt maintenance, and to have backup support organized in other equipment and at other institutions if equipment should break down.
    No preview · Article · Sep 2003
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    ABSTRACT: Purpose: Radiation therapy is an established method for treatment of early glottic cancers. Since the larynx is a thin wedge-shaped structure in the anterior neck adjacent to the airway, the absorbed doses to the lesion may be diminished because of build-up and build-down. The dose has been measured with conventional measuring systems such as thermoluminescent dosimetry (TLD). In this study, we employed Gafchromic MD-55-2 film (Nuclear Associates, Inc) as a dosimeter, for it can be set on the area of interest and with a measurability of a dose range of 3 to 100 Gy, and this radiometer material is similar in soft tissue of the human body. The dose distributions to the larynx were investigated with this film using a neck phantom under radiation beam energies of 4, 6 and 10 MV X-rays. Material and Method: The neck phantom was irradiated using 4, 6 and 10 MV X-rays, each with right and left lateral parallel-opposed fields, total radiation dose of 20 Gy, field size of 6 cm × 6 cm and 15 degrees wedge filter. Result: As a result, we observed secondary build-up and build-down curves in tissue in the vicinity of air cavities, especially at 10 MV X-rays. In the anterior commissure · center of glottic region, the absorbed doses decreasing rates of absorbed dose to 20 Gy with 4, 6, and 10 MV X-rays were 6.15% · 7.35%, 8.90% · 9.45% and 15.6% · 12.7% respectively. Conclusion: These findings suggest that patients with early glottic cancer with anterior commissure invasion may receive more effective treatment with 4 MV X-rays rather than with 6 MV or 10 MV X-rays.
    No preview · Article · Dec 2002 · Journal of JASTRO

  • No preview · Article · Nov 2001 · International journal of radiation oncology, biology, physics
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    ABSTRACT: PURPOSE/AIM The purpose of this exhibit is: 1. To understand of visual absorption spectrum of the Gafchromic EBT film 2. To demonstrate the specialized infrared flat-bed scanner for Gafchromic EBT film 3. To emphasize the usefulness of sensitivity and light source wavelength region of densitometer for the Gafchromic EBT film high-accuracy dosimetry CONTENT ORGANIZATION 1. Historical background of Gafchromic dosimeters 2. Gafchromic EBT film (EBT) - Configuration and structure - Characteristics 3. Densitometer and Spectrophotometer Measurement - Infrared flat-bed scanner with a transparency unit - Measurement - Performance data - Scanning - Luminescence spectrum measurement of a light source 4. Sensitometric response - Dose response curves - Dose sensitivity curves 5. Summary procedures for Gafchromic EBT film dosimetry 6. Future directions SUMMARY We developed an infrared flat-bed scanner with a transparency unit (IR scanner) in order to increase the sensitivity of measuring density of EBT. We demonstrate the usefulness of IR scanner for EBT. EBT using IR scanner was about 1.60 times more sensitive than using previous flat-bed scanner in the dose range from 0.3 Gy to 10 Gy. IR scanner can produce high sensitivity and accurate dosimetry for EBT. Our device may facilitate many applications of EBTs in high-resolution dose verification.
    No preview · Conference Paper ·
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    ABSTRACT: PURPOSE/AIM The purpose of this exhibit is: 1. To raise the problems of dose management by change of mammography equipment 2. To explain the utility of a new measuring method for an individual patients dose "Average Glandular Dose" (AGD) in mammography. 3. To review the patient dose in digital and screen-film mammography in a facility CONTENT ORGANIZATION A. Digital mammography and screen-film mammography B. Problems of dose management in mammography C. Method of individual patient's dose D. Clinical factors for patient's dose E. Future directions and summary SUMMARY The major teaching points of this exhibit are: 1. The greatest clinical factor which makes a patient dose increase is a compressed breast thickness 2. By adjustment of image quality for digital mammography, the patient dose will be higher than the screen-film system 3. When changing mammography method equipment, patient dose management is required. 4. In order to manage a patient dose, it is effective to measure a patient's individual dose
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