モンテカルロシミュレーションを用いた診断X線のコンクリート透過率の評価

取得学位 : 博士（保健学）, 学位授与番号 : 医博甲第2061号 , 学位授与年月日 : 平成21年9月28日, 学位授与大学 : 金沢大学, 審査結果の報告日 : 平成21年8月24

一般撮影での傾向

金沢大学附属病院放射線部((2)我が国での診断領域の患者被曝の現状-X線診断時に患者が受ける線量の調査研究より-,討論会テーマ:X線診断領域におけるデジタル化と被曝防護を考える,部会・分科会(関東部会,放射線防護分科会,計測分科会)合同シンポジウム

患者線量の測定および評価

金沢大学附属病院放射線部(計測,テーマ:撮影技術の過去から未来への継承～画質と線量の標準化を目指して～,専門分科会合同シンポジウム

X線CT装置の漏えい線量計算の新手法の開発

金沢大学附属病院本研究の概要は, 病院に新たに設置するX線CT装置(以下, CT)の事前安全評価である遮へい計算に関する内容であり医療安全に関わる重要なテーマである. 遮へい計算には壁材などの遮へい材のX線に対する正確な透過率が必要である. 現行法令の透過率はレントゲン装置のX線エネルギー(約30keV)を想定しており, CTのそれ(約50keV)では過小評価の可能性がある. 特にCT本体を通過するX線が存在すると濾過作用によりエネルギーが非常に高くなるためさらに過小評価となる. そこで, CT本体から漏洩するX線エネルギー成分を解明しそれに対応した遮へい材の透過率データを構築する.研究課題/領域番号:20H01167, 研究期間(年度):2020-04-01 – 2021-03-31出典：研究課題「X線CT装置の漏えい線量計算の新手法の開発」課題番号20H01167（KAKEN：科学研究費助成事業データベース（国立情報学研究所）） （https://kaken.nii.ac.jp/ja/grant/KAKENHI-PROJECT-20H01167/）を加工して作

Comparison of the Motion Accuracy of a Six Degrees of Freedom Radiotherapy Couch with and without Weights

In this study, we compared the motion accuracy of a six degrees of freedom (6D) couch for precision radiotherapy with or without weights attached to the couch. Two digital cameras were focused on the iso-center of a linear accelerator. Images of a needle which had been fixed to the 6D couch were obtained using the cameras when the couch moved in translation and rotation around each axis. The three-dimensional (3D) coordinates of the needle were calculated from coordinate values in the images. A coordinate error of the needle position relative to the theoretical position was calculated. The errors were obtained with or without a 60 kg weight attached to the 6D couch, and these errors were compared with each other. The mean distance of the 3D error vectors for the weighted test was 0.21 ± 0.11 mm, and >0.16 ± 0.09 mm for the non-weighted test (p < 0.05). However, the difference of two values was 0.06 mm which is smaller than the minimum distance the 6D couch system can correctly move. The variance of 0.16 mm for the Y coordinate errors for the weighted test only was larger than that for the non-weighted test, which was 0.06 mm (p < 0.05). We found that a total weight of 60 kg did not affect the accuracy of the 6D couch clinically. However, the variance of the Y coordinate errors was increased. This might suggest that the addition of this weight increased the uncertainty of the motion of the 6D couch

A metric for evaluation of deformable image registration

We propose a new metric, local uncertainty (LU), for the evaluation of deformable image registration (DIR) for dose accumulation in radiotherapy. LU measures the uncertainty of placement of each voxel in an image set after a DIR. The underlying concept of LU is that the distance between a focused voxel and a surrounding voxel on an image feature such as an edge is unchanged locally when the organ that includes these voxels is deformed. A candidate for the focused voxel after DIR can be calculated from three surrounding voxels and their distances. The positions of the candidates of the focused voxel calculated from several groups of any three surrounding voxels would vary. The variation of candidate positions indicates uncertainty of the focused voxel position. Thus, the standard deviation of candidate positions is treated as an LU value. The LU can be calculated in uniform signal regions. Assessment of DIR results in such regions is important for dose accumulation. The LU calculation was applied to a pair of computed tomography (CT) head and neck examinations after DIR. These CT examinations were for the initial radiotherapy planning and re-planning for a treatment course where the tumor underwent shrinkage during treatment. We generated an LU image showing high LU values in the shrinking tumor region and low LU values in undeformable bone. We have proposed the LU as a new metric for DIR

Long-term stability of the Hounsfield unit to electron density calibration curve in cone-beam computed tomography images for adaptive radiotherapy treatment planning

Aim To use cone-beam computed tomography (CBCT) images for treatment planning, the Hounsfield unit (HU)-electron density (ED) calibration table for CBCT should be stable. The purpose of this study was to verify the stability of the HU values for the CBCT system over 1 year and to evaluate the effects of variation in HU-ED calibration curves on dose calculation. Materials and Methods A tissue characterisation phantom was scanned with the field of view (FOV) of size S (FOV-S) and FOV of size M (FOV-M) using the CBCT system once a month for 1 year. A single field treatment plan was constructed on digital phantom images to validate the dose distribution using mean HU-ED calibration curves and possible variations. Results HU values for each material rod over the observation period varied with trend. The HU value of the cortical bone rod decreased by about 100 HU for the FOV-S and by about 300 HU for the FOV-M. Possible variation in the HU-ED calibration curves produced a ≤17·9% dose difference in the dose maximum in the treatment plan. Conclusions The CBCT system should be calibrated periodically for consistent dose calculation. © Cambridge University Press 2015. Aim To use cone-beam computed tomography (CBCT) images for treatment planning, the Hounsfield unit (HU)-electron density (ED) calibration table for CBCT should be stable. The purpose of this study was to verify the stability of the HU values for the CBCT system over 1 year and to evaluate the effects of variation in HU-ED calibration curves on dose calculation. Materials and Methods A tissue characterisation phantom was scanned with the field of view (FOV) of size S (FOV-S) and FOV of size M (FOV-M) using the CBCT system once a month for 1 year. A single field treatment plan was constructed on digital phantom images to validate the dose distribution using mean HU-ED calibration curves and possible variations. Results HU values for each material rod over the observation period varied with trend. The HU value of the cortical bone rod decreased by about 100 HU for the FOV-S and by about 300 HU for the FOV-M. Possible variation in the HU-ED calibration curves produced a ≤17·9% dose difference in the dose maximum in the treatment plan. Conclusions The CBCT system should be calibrated periodically for consistent dose calculation. © Cambridge University Press 2015

Impact of pitch angle setup error and setup error correction on dose distribution in volumetric modulated arc therapy for prostate cancer

In volumetric modulated arc therapy (VMAT) for prostate cancer, a positional and rotational error correction is performed according to the position and angle of the prostate. The correction often involves body leaning, and there is concern regarding variation in the dose distribution. Our purpose in this study was to evaluate the impact of body pitch rotation on the dose distribution regarding VMAT. Treatment plans were obtained retrospectively from eight patients with prostate cancer. The body in the computed tomography images for the original VMAT plan was shifted to create VMAT plans with virtual pitch angle errors of ±1.5° and ±3°. Dose distributions for the tilted plans were recalculated with use of the same beam arrangement as that used for the original VMAT plan. The mean value of the maximum dose differences in the dose distributions between the original VMAT plan and the tilted plans was 2.98 ± 0.96 %. The value of the homogeneity index for the planning target volume (PTV) had an increasing trend according to the pitch angle error, and the values of the D95 for the PTV and D2ml, V50, V60, and V70 for the rectum had decreasing trends (p < 0.05). However, there was no correlation between differences in these indexes and the maximum dose difference. The pitch angle error caused by body leaning had little effect on the dose distribution; in contrast, the pitch angle correction reduced the effects of organ displacement and improved these indexes. Thus, the pitch angle setup error in VMAT for prostate cancer should be corrected. © 2016 Japanese Society of Radiological Technology and Japan Society of Medical PhysicsEmbargo Perios 12 month