Fujio Araki

Kumamoto University, Kumamoto, Kumamoto, Japan

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Publications (73)111.87 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This study verified the dose calculation accuracy of the analytical anisotropic algorithm (AAA), Acuros XB version 10 (AXB10), and version 11 (AXB11) installed in an Eclipse treatment planning system, by comparing with Monte Carlo (MC) simulations. First, the algorithms were compared in terms of dose distributions using four types of virtual heterogeneous multi-layer phantom for 6 and 15 MV photons. Next, the clinical head and neck intensity-modulated radiation therapy (IMRT) dose distributions for 6 MV photons were evaluated using dose volume histograms (DVHs) and three-dimensional gamma analysis. In percentage depth doses (PDDs) for virtual heterogeneous phantoms, AAA overestimated absorbed doses in the air cavity, bone, and aluminum in comparison with MC, AXB10, and AXB11. The PDDs of AXB10 almost agreed with those of MC and AXB11, except for the air cavity. The dose in the air cavity was higher for AXB10 than for AXB11, because their electron cutoff energies are set at 500 and 200 keV, respectively. For head and neck IMRT dose distributions, the D95 in the clinical target volume (CTV) for AAA was almost the same as that for AXB10 and was approximately 7 % larger than that for MC. Comparing each approach with MC using a criterion of 3 %/3 mm, the pass rates for AXB10, AXB11, and AAA were 92.4, 94.7, and 90.4 % in the CTV, respectively. In conclusion, AAA produces dose errors in heterogeneous regions, while AXB11 provides calculation accuracy comparable to MC. AXB10 overestimates the dose in regions that include an air cavity.
    Radiological Physics and Technology 10/2015; DOI:10.1007/s12194-015-0336-z
  • Fujio Araki · Takeshi Ohno · Kiyotaka Kakei · Shinji Kawamura ·

    09/2015; 1(3):037002. DOI:10.1088/2057-1976/1/3/037002
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    ABSTRACT: This study developed a dedicated real-time monitoring system to detect intra-fractional head motion in intracranial radiotherapy using pressure sensors. The dedicated real-time monitoring system consists of pressure sensors with a thickness of 0.6 mm and a radius of 9.1 mm, a thermoplastic mask, a vacuum pillow, and a baseplate. The four sensors were positioned at superior-inferior and right-left sides under the occipital area. The sampling rate of pressure sensors was set to 5 Hz. First, we confirmed that the relationship between the force and the displacement of the vacuum pillow follows Hook's law. Next, the spring constant for the vacuum pillow was determined from the relationship between the force given to the vacuum pillow and the displacement of the head, detected by Cyberknife target locating system (TLS) acquisitions in clinical application. Finally, the accuracy of our system was evaluated by using the 2 × 2 confusion matrix. The regression lines between the force, y, and the displacement, x, of the vacuum pillow were given by [Formula: see text], [Formula: see text], and [Formula: see text] when the degree of inner pressure was -12 kPa,-20 kPa, and -27 kPa, respectively. The spring constant of the vacuum pillow was 1.6 N mm(-1) from the 6D positioning data of a total of 2999 TLS acquisitions in 19 patients. Head motions of 1 mm, 1.5 mm, and 2 mm were detected in real-time with the accuracies of 67%, 84%, and 89%, respectively. Our system can detect displacement of the head continuously during every interval of TLS with a resolution of 1-2 mm without any radiation exposure.
    Physics in Medicine and Biology 09/2015; 60(18):7229-43. DOI:10.1088/0031-9155/60/18/7229 · 2.76 Impact Factor

  • 07/2015; 1(2):025203. DOI:10.1088/2057-1976/1/2/025203
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    ABSTRACT: The purpose of this study was to evaluate a single-scan protocol using Gafchromic EBT3 film (EBT3) by comparing it with the commonly used 24-hr measurement protocol for radiochromic film dosimetry. Radiochromic film is generally scanned 24 hr after film exposure (24-hr protocol). The single-scan protocol enables measurement results within a short time using only the verification film, one calibration film, and unirradiated film. The single-scan protocol was scanned 30 min after film irradiation. The EBT3 calibration curves were obtained with the multichannel film dosimetry method. The dose verifications for each protocol were performed with the step pattern, pyramid pattern, and clinical treatment plans for intensity-modulated radiation therapy (IMRT). The absolute dose distributions for each protocol were compared with those calculated by the treatment planning system (TPS) using gamma evaluation at 3% and 3 mm. The dose distribution for the single-scan protocol was within 2% of the 24-hr protocol dose distribution. For the step pattern, the absolute dose discrepancies between the TPS for the single-scan and 24-hr protocols were 2.0 ± 1.8 cGy and 1.4 ± 1.2 cGy at the dose plateau, respectively. The pass rates were 96.0% for the single-scan protocol and 95.9% for the 24-hr protocol. Similarly, the dose discrepancies for the pyramid pattern were 3.6 ± 3.5cGy and 2.9 ± 3.3 cGy, respectively, while the pass rates for the pyramid pattern were 95.3% and 96.4%, respectively. The average pass rates for the four IMRT plans were 96.7% ± 1.8% for the single-scan protocol and 97.3% ± 1.4% for the 24-hr protocol. Thus, the single-scan protocol measurement is useful for dose verification of IMRT, based on its accuracy and efficiency.
    Journal of Applied Clinical Medical Physics 06/2015; 16(2):5226. DOI:10.1120/jacmp.v16i2.5226 · 1.17 Impact Factor
  • F Araki · T Ohno · R Onitsuka · Y Shimohigashi ·
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    ABSTRACT: To investigate dosimetric properties in high-energy photon beams for a Solid Water High Equivalency (SWHE, SW557) phantom (Gammex) which was newly developed as water mimicking material. The mass density of SWHE and SWHE/water electron density ratio are 1.032 g/cm(3) and 1.005 according to the manufacturer information, respectively. SWHE is more water equivalent material in physical characteristics and uniformity than conventional SW457. This study calculated the relative ionization ratio of water and SWHE as a function of depth from the cavity dose in PTW30013 and Exradin A19 Farmer-type ionization chambers using Monte Caro simulations. The simulation was performed with a 10 x 10 cm(2) field at SAD of 100 cm for 4, 6, 10, 15, and 18 MV photons. The ionization ratio was also measured with the PTW30013 chamber for 6 and 15 MV photons. In addition, the overall perturbation factor of both chambers was calculated for both phantoms. The relative ionization ratio curves for water and SWHE was in good agreement for all photon energies. The ionization ratio of water/SWHE for both chambers was 0.999-1.002, 0.999-1.002, 1.001-1.004, 1.004-1.007, and 1.006-1.010 at depths of over the buildup region for 4, 6, 10, 15, and 18 MV photons, respectively. The ionization ratio of water/SWHE increased up to 1% with increasing the photon energy. The measured ionization ratio of water/SWHE for 6 and 15 MV photons agreed well with calculated values. The overall perturbation factor for both chambers was 0.983-0.988 and 0.978-0.983 for water and SWHE, respectively, in a range from 4 MV to 18 MV. The depth scaling factor of water/SWHE was equal to unity for all photon energies. The ionization ratio of water/SWHE at a reference depth was equal to unity for 4 and 6 MV and larger up to 0.7% than unity for 18 MV.
    Medical Physics 06/2015; 42(6):3410. DOI:10.1118/1.4924697 · 2.64 Impact Factor
  • T Ohno · F Araki ·
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    ABSTRACT: To compare dosimetric properties and patient organ doses from four commercial multidetector CT (MDCT) using Monte Carlo (MC) simulation based on the absorbed dose measured using a Farmer chamber and cylindrical water phantoms according to AAPM TG-111. Four commercial MDCT were modeled using the GMctdospp (IMPS, Germany) based on the EGSnrc user code. The incident photon spectrum and bowtie filter for MC simulations were determined so that calculated values of aluminum half-value layer (Al-HVL) and off-center ratio (OCR) profile in air agreed with measured values. The MC dose was calibrated from absorbed dose measurements using a Farmer chamber and cylindrical water phantoms. The dose distributions of head, chest, and abdominal scan were calculated using patient CT images and mean organ doses were evaluated from dose volume histograms. The HVLs at 120 kVp of Brilliance, LightSpeed, Aquilion, and SOMATOM were 9.1, 7.5, 7.2, and 8.7 mm, respectively. The calculated Al-HVLs agreed with measurements within 0.3%. The calculated and measured OCR profiles agreed within 5%. For adult head scans, mean doses for eye lens from Brilliance, LightSpeed, Aquilion, and SOMATOM were 21.7, 38.5, 47.2 and 28.4 mGy, respectively. For chest scans, mean doses for lung from Brilliance, LightSpeed, Aquilion, and SOMATOM were 21.1, 26.1, 35.3 and 24.0 mGy, respectively. For adult abdominal scans, the mean doses for liver from Brilliance, LightSpeed, Aquilion, and SOMATOM were 16.5, 21.3, 22.7, and 18.0 mGy, respectively. The absorbed doses increased with decreasing Al-HVL. The organ doses from Aquilion were two greater than those from Brilliance in head scan. MC dose distributions based on absorbed dose measurement in cylindrical water phantom are useful to evaluate individual patient organ doses.
    Medical Physics 06/2015; 42(6):3542. DOI:10.1118/1.4925245 · 2.64 Impact Factor
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    ABSTRACT: The aim of this study was to develop new dosimetry with cylindrical water phantoms for multidetector computed tomography (MDCT). The ionization measurement was performed with a Farmer ionization chamber at the center and four peripheral points in the body-type and head-type cylindrical water phantoms. The ionization was converted to the absorbed dose using a (60)Co absorbed-dose-to-water calibration factor and Monte Carlo (MC) -calculated correction factors. The correction factors were calculated from MDCT (Brilliance iCT, 64-slice, Philips Electronics) modeled with GMctdospp (IMPS, Germany) software based on the EGSnrc MC code. The spectrum of incident x-ray beams and the configuration of a bowtie filter for MDCT were determined so that calculated photon intensity attenuation curves for aluminum (Al) and calculated off-center ratio (OCR) profiles in air coincided with those measured. The MC-calculated doses were calibrated by the absorbed dose measured at the center in both cylindrical water phantoms. Calculated doses were compared with measured doses at four peripheral points and the center in the phantom for various beam pitches and beam collimations. The calibration factors and the uncertainty of the absorbed dose determined using this method were also compared with those obtained by CTDIair (CT dose index in air). Calculated Al half-value layers and OCRs in air were within 0.3% and 3% agreement with the measured values, respectively. Calculated doses at four peripheral points and the centers for various beam pitches and beam collimations were within 5% and 2% agreement with measured values, respectively. The MC-calibration factors by our method were 44-50% lower than values by CTDIair due to the overbeaming effect. However, the calibration factors for CTDIair agreed within 5% with those of our method after correction for the overbeaming effect. Our method makes it possible to directly measure the absorbed dose for MDCT and is more robust and accurate than the CTDIair measurement.
    Physics in Medicine and Biology 05/2015; 60(11):4517-4531. DOI:10.1088/0031-9155/60/11/4517 · 2.76 Impact Factor

  • Physics in Medicine and Biology 01/2015; 60(2):929-929. DOI:10.1088/0031-9155/60/2/929 · 2.76 Impact Factor
  • Fujio Araki · Takeshi Ohno ·
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    ABSTRACT: This study investigated the response of a radiophotoluminescent glass dosimeter (RGD) in megavoltage photon and electron beams. The RGD response was compared with ion chamber measurements for 4-18 MV photons and 6-20 MeV electrons in plastic water phantoms. The response was also calculated via Monte Carlo (MC) simulations with EGSnrc/egs_chamber and Cavity user-codes, respectively. In addition, the response of the RGD cavity was analyzed as a function of field sizes and depths according to Burlin's general cavity theory. The perturbation correction factor, PQ, in the RGD cavity was also estimated from MC simulations for photon and electron beams. The calculated and measured RGD energy response at reference conditions with a 10 × 10 cm(2) field and 10 cm depth in photons was lower by up to 2.5% with increasing energy. The variation in RGD response in the field size range of 5 × 5 cm(2) to 20 × 20 cm(2) was 3.9% and 0.7%, at 10 cm depth for 4 and 18 MV, respectively. The depth dependence of the RGD response was constant within 1% for energies above 6 MV but it increased by 2.6% and 1.6% for a large (20 × 20 cm(2)) field at 4 and 6 MV, respectively. The dose contributions from photon interactions (1 - d) in the RGD cavity, according to Burlin's cavity theory, decreased with increasing energy and decreasing field size. The variation in (1 - d) between field sizes became larger with increasing depth for the lower energies of 4 and 6 MV. PQ for the RGD cavity was almost constant between 0.96 and 0.97 at 10 MV energies and above. Meanwhile, PQ depends strongly on field size and depth for 4 and 6 MV photons. In electron beams, the RGD response at a reference depth, dref, varied by less than 1% over the electron energy range but was on average 4% lower than the response for 6 MV photons. The RGD response for photon beams depends on both (1 - d) and perturbation effects in the RGD cavity. Therefore, it is difficult to predict the energy dependence of RGD response by Burlin's theory and it is recommended to directly measure RGD response or use the MC-calculated RGD response, regarding the practical use. The response for electron beams decreased rapidly at a depth beyond dref for lower mean electron energies <3 MeV and in contrast PQ increased.
    Medical Physics 12/2014; 41(12):122102. DOI:10.1118/1.4901639 · 2.64 Impact Factor
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    ABSTRACT: This study investigated the accuracy of positioning and irradiation targeting for multiple off-isocenter targets in intracranial image-guided radiation therapy (IGRT). A phantom with nine circular targets was created to evaluate both accuracies. First, the central point of the isocenter target was positioned with a combination of an ExacTrac x-ray (ETX) and a 6D couch. The positioning accuracy was determined from the deviations of coordinates of the central point in each target obtained from the kV-cone beam computed tomography (kV-CBCT) for IGRT and the planning CT. Similarly, the irradiation targeting accuracy was evaluated from the deviations of the coordinates between the central point of each target and the central point of each multi-leaf collimator (MLC) field for multiple targets. Secondly, the 6D couch was intentionally rotated together with both roll and pitch angles of 0.5° and 1° at the isocenter and similarly the deviations were evaluated. The positioning accuracy for all targets was less than 1 mm after 6D positioning corrections. The irradiation targeting accuracy was up to 1.3 mm in the anteroposterior (AP) direction for a target 87 mm away from isocenter. For the 6D couch rotations with both roll and pitch angles of 0.5° and 1°, the positioning accuracy was up to 1.0 mm and 2.3 mm in the AP direction for the target 87 mm away from the isocenter, respectively. The irradiation targeting accuracy was up to 2.1 mm and 2.6 mm in the AP direction for the target 87 mm away from the isocenter, respectively. The off-isocenter irradiation targeting accuracy became worse than the positioning accuracy. Both off-isocenter accuracies worsened in proportion to rotation angles and the distance from the isocenter to the targets. It is necessary to examine the set-up margin for off-isocenter multiple targets at each institution because irradiation targeting accuracy is peculiar to the linac machine.
    Physics in Medicine and Biology 11/2014; 59(24):7753-7766. DOI:10.1088/0031-9155/59/24/7753 · 2.76 Impact Factor
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    ABSTRACT: In this study, we develope a novel method to directly evaluate an absorbed dose-to-water for kilovoltage-cone beam computed tomography (kV-CBCT) in image-guided radiation therapy (IGRT). Absorbed doses for the kV-CBCT systems of the Varian On-Board Imager (OBI) and the Elekta X-ray Volumetric Imager (XVI) were measured by a Farmer ionization chamber with a 60Co calibration factor. The chamber measurements were performed at the center and four peripheral points in body-type (30 cm diameter and 51 cm length) and head-type (16 cm diameter and 33 cm length) cylindrical water phantoms. The measured ionization was converted to the absorbed dose-to-water by using a 60Co calibration factor and a Monte Carlo (MC)-calculated beam quality conversion factor, kQ, for 60Co to kV-CBCT. The irradiation for OBI and XVI was performed with pelvis and head modes for the body- and the head-type phantoms, respectively. In addition, the dose distributions in the phantom for both kV-CBCT systems were calculated with MC method and were compared with measured values. The MC-calculated doses were calibrated at the center in the water phantom and compared with measured doses at four peripheral points. The measured absorbed doses at the center in the body-type phantom were 1.96 cGy for OBI and 0.83 cGy for XVI. The peripheral doses were 2.36–2.90 cGy for OBI and 0.83–1.06 cGy for XVI. The doses for XVI were lower up to approximately one-third of those for OBI. Similarly, the measured doses at the center in the head-type phantom were 0.48 cGy for OBI and 0.21 cGy for XVI. The peripheral doses were 0.26–0.66 cGy for OBI and 0.16–0.30 cGy for XVI. The calculated peripheral doses agreed within 3% in the pelvis mode and within 4% in the head mode with measured doses for both kV-CBCT systems. In addition, the absorbed dose determined in this study was approximately 4% lower than that in TG-61 but the absorbed dose by both methods was in agreement within their combined uncertainty. This method is more robust and accurate compared to the dosimetry based on a conventional air-kerma calibration factor. Therefore, it is possible to be used as a standard dosimetry protocol for kV-CBCT in IGRT.
    Physics in Medicine and Biology 11/2014; 59(23):7297. DOI:10.1088/0031-9155/59/23/7297 · 2.76 Impact Factor
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    ABSTRACT: Our purpose in this study was to evaluate the performance of four-dimensional computed tomography (4D-CBCT) and to optimize the acquisition parameters. We evaluated the relationship between the acquisition parameters of 4D-CBCT and the accuracy of the target motion trajectory using a dynamic thorax phantom. The target motion was created three dimensionally using target sizes of 2 and 3 cm, respiratory cycles of 4 and 8 s, and amplitudes of 1 and 2 cm. The 4D-CBCT data were acquired under two detector configurations: "small mode" and "medium mode". The projection data acquired with scan times ranging from 1 to 4 min were sorted into 2, 5, 10, and 15 phase bins. The accuracy of the measured target motion trajectories was evaluated by means of the root mean square error (RMSE) from the setup values. For the respiratory cycle of 4 s, the measured trajectories were within 2 mm of the setup values for all acquisition times and target sizes. Similarly, the errors for the respiratory cycle of 8 s were <4 mm. When we used 10 or more phase bins, the measured trajectory errors were within 2 mm of the setup values. The trajectory errors for the two detector configurations showed similar trends. The acquisition times for achieving an RMSE of 1 mm for target sizes of 2 and 3 cm were 2 and 1 min, respectively, for respiratory cycles of 4 s. The results obtained in this study enable optimization of the acquisition parameters for target size, respiratory cycle, and desired measurement accuracy.
    Radiological Physics and Technology 10/2014; 8(1). DOI:10.1007/s12194-014-0296-8
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    ABSTRACT: In this study, we evaluated the dosimetric performance of the three-dimensional (3D) dose verification system, COMPASS version 3 (IBA Dosimetry, GmbH, Germany). The COMPASS has the function of a dedicated beam modeling and dose calculation. It is able to reconstruct 3D dose distributions on patient CT images, using the incident fluence from a linear accelerator measured with the MatriXX 2D array (IBA Dosimetry). The dose profiles measured with various multi-leaf collimator (MLC) test patterns for the COMPASS were checked by comparison with those of EDR2 (Eastman Kodak, Rochester, NY) films and Monte Carlo (MC) simulations. The COMPASS was also used for dose verification in clinical intensity-modulated radiation therapy (IMRT) plans for head and neck cases. The dose distributions were compared with those measured by 3DVH (Sun Nuclear, Melbourne, FL) and MC. In addition, the quality assurance (QA) times among the COMPASS, 3DVH, and EDR2 were compared. For MLC test patterns, the COMPASS dose profiles agreed within 3 % with those of EDR2 films and MC simulations. The physical resolution of the COMPASS detectors was lower than that of film, but the dose resolution for MLC patterns was comparable to that of film. In clinical plans, the dose-volume-histograms were equal for all systems. The average QA times of the COMPASS, 3DVH, and EDR2 film were 40.1, 59.4, and 121.4 min, respectively. The COMPASS system provides fast and reliable 3D dose verification for clinical IMRT QA. The COMPASS QA process does not require phantom plans. Therefore, it allows a simple QA workflow.
    Radiological Physics and Technology 09/2014; 8(1). DOI:10.1007/s12194-014-0294-x
  • T Ono · F Araki ·

    Medical Physics 06/2014; 41(6):136-136. DOI:10.1118/1.4887976 · 2.64 Impact Factor
  • F Araki · R Onizuka · T Ohno · Y Tomiyama · K Hioki ·
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    ABSTRACT: Purpose: To investigate the accuracy of the Acuros XB version 11 (AXB11) advanced dose calculation algorithm by comparing with Monte Caro (MC) calculations. The comparisons were performed with dose distributions for a virtual inhomogeneity phantom and intensity-modulated radiotherapy (IMRT) in head and neck.
    Medical Physics 06/2014; 41(6):296-296. DOI:10.1118/1.4888646 · 2.64 Impact Factor
  • Yuuki Tomiyama · Fujio Araki · Takeshi Oono · Kazunari Hioki ·
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    ABSTRACT: Our purpose in this study was to implement three-dimensional (3D) gamma analysis for structures of interest such as the planning target volume (PTV) or clinical target volume (CTV), and organs at risk (OARs) for intensity-modulated radiation therapy (IMRT) dose verification. IMRT dose distributions for prostate and head and neck (HN) cancer patients were calculated with an analytical anisotropic algorithm in an Eclipse (Varian Medical Systems) treatment planning system (TPS) and by Monte Carlo (MC) simulation. The MC dose distributions were calculated with EGSnrc/BEAMnrc and DOSXYZnrc user codes under conditions identical to those for the TPS. The prescribed doses were 76 Gy/38 fractions with five-field IMRT for the prostate and 33 Gy/17 fractions with seven-field IMRT for the HN. TPS dose distributions were verified by the gamma passing rates for the whole calculated volume, PTV or CTV, and OARs by use of 3D gamma analysis with reference to MC dose distributions. The acceptance criteria for the 3D gamma analysis were 3/3 and 2 %/2 mm for a dose difference and a distance to agreement. The gamma passing rates in PTV and OARs for the prostate IMRT plan were close to 100 %. For the HN IMRT plan, the passing rates of 2 %/2 mm in CTV and OARs were substantially lower because inhomogeneous tissues such as bone and air in the HN are included in the calculation area. 3D gamma analysis for individual structures is useful for IMRT dose verification.
    Radiological Physics and Technology 05/2014; 7(2). DOI:10.1007/s12194-014-0266-1
  • Takeshi Oono · Fujio Araki · Shoya Tsuduki · Keiichi Kawasaki ·
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    ABSTRACT: In this study, we aimed to evaluate quantitatively the patient organ dose from computed tomography (CT) using Monte Carlo calculations. A multidetector CT unit (Aquilion 16, TOSHIBA Medical Systems) was modeled with the GMctdospp (IMPS, Germany) software based on the EGSnrc Monte Carlo code. The X-ray spectrum and the configuration of the bowtie filter for the Monte Carlo modeling were determined from the chamber measurements for the half-value layer (HVL) of aluminum and the dose profile (off-center ratio, OCR) in air. The calculated HVL and OCR were compared with measured values for body irradiation with 120 kVp. The Monte Carlo-calculated patient dose distribution was converted to the absorbed dose measured by a Farmer chamber with a (60)Co calibration factor at the center of a CT water phantom. The patient dose was evaluated from dose-volume histograms for the internal organs in the pelvis. The calculated Al HVL was in agreement within 0.3 % with the measured value of 5.2 mm. The calculated dose profile in air matched the measured value within 5 % in a range of 15 cm from the central axis. The mean doses for soft tissues were 23.5, 23.8, and 27.9 mGy for the prostate, rectum, and bladder, respectively, under exposure conditions of 120 kVp, 200 mA, a beam pitch of 0.938, and beam collimation of 32 mm. For bones of the femur and pelvis, the mean doses were 56.1 and 63.6 mGy, respectively. The doses for bone increased by up to 2-3 times that of soft tissue, corresponding to the ratio of their mass-energy absorption coefficients.
    Radiological Physics and Technology 11/2013; 7(1). DOI:10.1007/s12194-013-0250-1
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    ABSTRACT: Purpose: In this study, a dedicated device for ion chamber measurements of absorbed dose-to-water for a Nucletron microSelectron-v2 HDR (192)Ir brachytherapy source is presented. The device uses two ionization chambers in a so-called sandwich assembly. Using this setup and by taking the average reading of the two chambers, any dose error due to difficulties in absolute positioning (centering) of the source in between the chambers is cancelled to first order. The method's accuracy was examined by comparing measurements with absorbed dose-to-water determination based on the AAPM TG-43 protocol. Methods: The optimal source-to-chamber distance (SCD) for (192)Ir dosimetry was determined from ion chamber measurements in a water phantom. The (192)Ir source was sandwiched between two Exradin A1SL chambers (0.057 cm(3)) at the optimal SCD separation. The measured ionization was converted to the absorbed dose-to-water using a (60)Co calibration factor and a Monte Carlo-calculated beam quality conversion factor, kQ, for (60)Co to (192)Ir. An uncertainty estimate of the proposed method was determined based on reproducibility of measurements at different institutions for the same type of source. Results: The optimal distance for the A1SL chamber measurements was determined to be 5 cm from the (192)Ir source center, considering the depth dependency of kQ for (60)Co to (192)Ir and the chamber positioning. The absorbed dose to water measured at (5 cm, 90°) on the transverse axis was 1.3% lower than TG-43 values and its reproducibility and overall uncertainty were 0.8% and 1.7%, respectively. The measurement doses at anisotropic points agreed within 1.5% with TG-43 values. Conclusions: The ion chamber measurement of absorbed dose-to-water with a sandwich method for the (192)Ir source provides a more accurate, direct, and reference dose compared to the dose-to-water determination based on air-kerma strength in the TG-43 protocol. Due to the simple but accurate assembly, the sandwich measurement method is useful for daily dose management of (192)Ir sources.
    Medical Physics 09/2013; 40(9):092101. DOI:10.1118/1.4816673 · 2.64 Impact Factor
  • Yuji Nakaguchi · Takeshi Oono · Fujio Araki · Masato Maruyama ·
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    ABSTRACT: In this article, we present a physical characterization of the agility(™) (Elekta). agility(™) is composed of 160 interdigitating multileaf collimators (MLCs) with a width of 5 mm at the isocenter. The physical characterizations that include leaf position accuracy, leakage, field penumbra and the tongue-and-groove (T&G) effect were evaluated using well-commissioned 4, 6 and 10-MV photon beams. The leaf position accuracy was within 0.5 mm for all gantry angles and each MLC. The leakage was 0.44% on average and reached 0.47% at 10 MV: remarkably low due to a new design with tilted leaves. However, the T&G effect occurred due to tilt. It was approximately 20.8% on average and reached 22.3% at 6 MV. The penumbra width increased up to 8.5 mm at a field size of 20×20 cm at 4 MV. High position designed MLCs create a wider penumbra but show lower leakage and large head clearance. Head clearance is an important factor in stereotactic radiotherapy with multiple non-coplanar beams.
    Nippon Hoshasen Gijutsu Gakkai zasshi 07/2013; 69(7):778-83. DOI:10.6009/jjrt.2013_JSRT_69.7.778

Publication Stats

224 Citations
111.87 Total Impact Points


  • 2003-2015
    • Kumamoto University
      • • Faculty of Life Sciences
      • • Graduate School of Health Sciences
      • • Department of Health Care Science
      • • School of Medicine
      Kumamoto, Kumamoto, Japan
  • 2004
    • University of California, Davis
      Davis, California, United States
  • 2002
    • California State University, Sacramento
      Sacramento, California, United States