Biomedical subjects

Tomoyasu Yashiro

Publications and source records attributed to Tomoyasu Yashiro.

4 recordsLinked to original sources

PubMed2006

Four-dimensional measurement of lung tumor displacement using 256-multi-slice CT-scanner.

The concept of internal target volume is of marked importance for radiotherapy to lung tumors as respiration-induced motion is important. Individualized assessment of motion is required as tumor site may not predict the extent or pattern of tumor motion. We performed volumetric cine scanning using the 256-multi-slice CT (256MSCT) to study tumor motion during free breathing in 14 inpatients who were treated with carbon-ion radiotherapy. Motion assessment in 16 respiratory phases of the cine CT revealed most tumors to show hysteresis-like behavior. Isocenter displacement between peak exhalation and inhalation for the average of the right and left lungs were 7 mm, 7 mm and 15 mm for the upper, middle and lower lobes, respectively. Cine CT with the 256MSCT improved the evaluation of tumor displacement and overcomes some of the limitations associated with current CT methods. Volumetric cine CT data provides useful data on motion for planning in all radiation approaches for lung tumors.

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PubMed2006

Respiratory correlated segment reconstruction algorithm towards four-dimensional radiation therapy using carbon ion beams.

PURPOSE: To enhance the precision of treatment planning for tumors which move under respiration, we developed a respiratory-correlated segment reconstruction method (RS) based on the Feldkamp--Davis--Kress algorithm (FDK) which provides high temporal resolution and a high signal-to-noise ratio. We compared full-scan (FS-FDK) and RS-FDK with regard to dose distribution in heavy ion treatment planning. MATERIALS AND METHODS: Data acquisition for RS-FDK is done using a respiratory sensing system in cine scan mode with a 256-multi-detector row CT (256-MDCT). To evaluate the accuracy of irradiation of moving tumors, dose distributions with each algorithm were compared in heavy ion treatment planning using beam parameters obtained with FS-FDK. RESULTS: Images obtained using RS-FDK did not show motion artifacts and visualized the edges of the liver and pulmonary vessels more clearly than those with FS-FDK. The iso-dose distributions for FS-FDK covered the target volume; in contrast, RS-FDK with the beam parameter of FS-FDK image provided an insufficient dose to the target and a considerable dose to normal tissues around it. CONCLUSIONS: The information provided by RS-FDK improves accuracy in the prescription of dose-to-target volume. Further, RS-FDK allows greater precision in the delivery of radiotherapy, including 4D radiation therapy.

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PubMed2006

A combination-weighted Feldkamp-based reconstruction algorithm for cone-beam CT.

The combination-weighted Feldkamp algorithm (CW-FDK) was developed and tested in a phantom in order to reduce cone-beam artefacts and enhance cranio-caudal reconstruction coverage in an attempt to improve image quality when utilizing cone-beam computed tomography (CBCT). Using a 256-slice cone-beam CT (256CBCT), image quality (CT-number uniformity and geometrical accuracy) was quantitatively evaluated in phantom and clinical studies, and the results were compared to those obtained with the original Feldkamp algorithm. A clinical study was done in lung cancer patients under breath holding and free breathing. Image quality for the original Feldkamp algorithm is degraded at the edge of the scan region due to the missing volume, commensurate with the cranio-caudal distance between the reconstruction and central planes. The CW-FDK extended the reconstruction coverage to equal the scan coverage and improved reconstruction accuracy, unaffected by the cranio-caudal distance. The extended reconstruction coverage with good image quality provided by the CW-FDK will be clinically investigated for improving diagnostic and radiotherapy applications. In addition, this algorithm can also be adapted for use in relatively wide cone-angle CBCT such as with a flat-panel detector CBCT.

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PubMed2004

Huge localized fibrous tumor of the pleura resembling a mediastinal tumor: report of a case.

A 67-year-old man was admitted to our hospital because of an abnormal chest echoic lesion detected incidentally by echocardiography. A chest roentgenogram showed the presence of a giant mass, and computed tomography of the chest confirmed the presence of a mass with a nonhomogeneous density in the left mediastinum, just adjacent to the left ventricle of the heart. Percutaneous aspiration cytology of the mass showed benign fibrous cells and a small amount of lymphocytes. The preoperative diagnosis of the tumor suggested a thymoma, and the patient underwent a thoracotomy. A pedunculated tumor arose from the visceral pleura of the left upper lobe of the lung, and it was capsulated within the pleura. The tumor measured 15 x 12 x 8 cm in size and it was successfully resected. The pathological diagnosis of the tumor was benign localized fibrous tumor of the pleura.

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