Biomedical subjects

Haruo Yamashita

Publications and source records attributed to Haruo Yamashita.

5 recordsLinked to original sources

PubMed2006

Extended collimator model for pencil-beam dose calculation in proton radiotherapy.

We have developed a simple collimator model to improve the accuracy of penumbra behaviour in pencil-beam dose calculation for proton radiotherapy. In this model, transmission of particles through a three-dimensionally extended opening of a collimator is calculated in conjunction with phase-space distribution of the particles. Comparison of the dose distributions calculated using the new three-dimensional collimator model and the conventional two-dimensional model to lateral dose profiles experimentally measured with collimated proton beams showed the superiority of the new model over the conventional one.

Algorithms↗

PubMed2005

Patient positioning method based on binary image correlation between two edge images for proton-beam radiation therapy.

A new technique based on normalized binary image correlation between two edge images has been proposed for positioning proton-beam radiotherapy patients. A Canny edge detector was used to extract two edge images from a reference x-ray image and a test x-ray image of a patient before positioning. While translating and rotating the edged test image, the absolute value of the normalized binary image correlation between the two edge images is iteratively maximized. Each time before rotation, dilation is applied to the edged test image to avoid a steep reduction of the image correlation. To evaluate robustness of the proposed method, a simulation has been carried out using 240 simulated edged head front-view images extracted from a reference image by varying parameters of the Canny algorithm with a given range of rotation angles and translation amounts in x and y directions. It was shown that resulting registration errors have an accuracy of one pixel in x and y directions and zero degrees in rotation, even when the number of edge pixels significantly differs between the edged reference image and the edged simulation image. Subsequently, positioning experiments using several sets of head, lung, and hip data have been performed. We have observed that the differences of translation and rotation between manual positioning and the proposed method were within one pixel in translation and one degree in rotation. From the results of the validation study, it can be concluded that a significant reduction in workload for the physicians and technicians can be achieved with this method.

Algorithms↗

PubMed2005

[Initial clinical experience of proton therapy at Shizuoka Cancer Center].

PURPOSE: To present the initial experience and preliminary clinical results of patients treated mainly with proton irradiation at the newly developed proton therapy facility at Shizuoka Cancer Center. MATERIALS AND METHODS: We reviewed 125 patients who underwent proton therapy between July 2003 and December 2004. Of these 125 patients, 11 had head and neck malignancies, 15 non-small cell lung cancers, 22 hepatocellular carcinomas, 62 prostate cancers, and 15 other malignant tumors. RESULTS: Most patients experienced Grade 0-1 acute morbidities (NCI-CTC) in skin or mucosa, while a temporary Grade 2-3 reaction was observed in a high dose area. Response rates were 73% for H & N malignancies, 100% for NSCLC, and 77% for HCC. PSA evaluation for patients with prostate cancer revealed a high rate of complete response. CONCLUSION: The efficacy and safety of proton therapy at Shizuoka Cancer Center was demonstrated for patients with early-stage cancer or locally advanced disease.

Adolescent↗

PubMed2002

Reconstruction of biologically equivalent dose distribution on CT-image from measured physical dose distribution of therapeutic beam in water phantom.

From the standpoint of quality assurance in radiotherapy, it is very important to compare the dose distributions realized by an irradiation system with the distribution planned by a treatment planning system. To compare the two dose distributions, it is necessary to convert the dose distributions on CT images to distributions in a water phantom or convert the measured dose distributions to distributions on CT images. Especially in heavy-ion radiotherapy, it is reasonable to show the biologically equivalent dose distribution on the CT images. We developed tools for the visualization and comparison of these distributions in order to check the therapeutic beam for each patient at the National Institute of Radiological Sciences (NIRS). To estimate the distribution in a patient, the dose is derived from the measurement by mapping it on a CT-image. Fitting the depth-dose curve to the calculated SOBP curve also gives biologically equivalent dose distributions in the case of a carbon beam. Once calculated, dose distribution information can be easily handled to make a comparison with the planned distribution and display it on a grey-scale CT-image. Quantitative comparisons of dose distributions can be made with anatomical information, which also gives a verification of the irradiation system in a very straightforward way.

Humans↗

PubMed2002

Cadaveric and clinical study of endoscope-assisted microneurosurgery for cerebral aneurysms using angle-type rigid endoscope.

Highly advanced optical equipment enables endoscopic surgery to be performed in neurosurgery. We developed an angle-type rigid endoscope having an angled shaft, and has performed endoscope-assisted surgery in neck clipping of 50 cerebral aneurysms. Anatomical study concerning the perforating branch was made through a pterional approach using 3 cadavers. By using endoscope, we can observe the posterior communicating artery and anterior choroidal artery behind the internal carotid artery without retract the internal carotid artery and the surrounding structures. Furthermore IIIrd~VIIIth cranial nerve in opposite side and basilar artery in the posterior fossa can be observed. As the clinical study, we used endoscope in 50 clipping of cerebral aneurysms (29 Internal carotid artery aneurysms, 6 anterior communicating artery aneurysms, 2 anterior cerebral artery aneurysms, 7 middle cerebral artery aneurysms, 5 vertebral artery-posterior inferior cerebellar artery aneurysm, and basilar bifurcation aneurysms). The endoscopic image showed in incomplete clipping in 2 cases, where additional clipping was then performed. In all subject, complete clipping was performed using both microscopic and endoscopic view. Use of the angle-type rigid endoscope together with Doppler ultrasound, should increase the feasibility of complete clipping procedure, resulting in reduced complication rate.

Adult↗