Chusin Thunyarat, Matsubara Kosuke, Takemura Akihiro, Okubo Rena, Ogawa Yoshinori
Department of Quantum Medical Technology, Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, Kanazawa, Japan.
Department of Radiological Technology, Faculty of Allied Health Sciences, Naresuan University, Phitsanulok, Thailand.
J Appl Clin Med Phys. 2019 Jan;20(1):340-347. doi: 10.1002/acm2.12486. Epub 2018 Nov 24.
Digital breast tomosynthesis (DBT) is an alternative tool for breast cancer screening; however, the magnitude of peripheral organs dose is not well known. This study aimed to measure scattered dose and estimate organ dose during mammography under conventional (CM) and Tomo (TM) modes in a specific DBT system. Optically stimulated luminescence dosimeters (OSLDs), whose responses were corrected using a parallel-plate ionization chamber, were pasted on the surface of custom-made polymethyl methacrylate (PMMA) and RANDO phantoms to measure entrance surface air kerma (ESAK). ESAK measurements were also acquired with a 4.5-cm thick breast phantom for a standard mammogram. Organ dose conversion factors (CF ) were determined as ratio of air kerma at a specific depth to that at the surface for the PMMA phantom and multiplied by the ratio of mass energy absorption coefficients of tissue to air. Normalized eye lens and thyroid gland doses were calculated using the RANDO phantom by multiplying CF and ESAK values. Maximum variability in OSLD response to scatter radiation from the DBT system was 33% in the W/Rh spectrum and variations in scattered dose distribution were observed between CM and TM. The CF values for eye lens and thyroid gland ranged between 0.58 to 0.66 and 0.29 to 0.33, respectively. Mean organ doses for two-view unilateral imaging were 0.24 (CM) and 0.18 (TM) μGy/mAs for the eye lens and 0.24 (CM) and 0.25 (TM) μGy/mAs for the thyroid gland. Higher organ doses were observed during TM compared to CM as the automatic exposure control (AEC) system resulted in greater total mAs values in TM.
数字乳腺断层合成（DBT）是一种用于乳腺癌筛查的替代工具；然而，外周器官剂量的大小尚不清楚。本研究旨在测量特定DBT系统在传统（CM）和断层合成（TM）模式下乳腺摄影期间的散射剂量并估算器官剂量。将响应通过平行板电离室校正的光激励发光剂量计（OSLD）粘贴在定制的聚甲基丙烯酸甲酯（PMMA）和RANDO体模表面，以测量入射表面空气比释动能（ESAK）。还使用4.5厘米厚的乳腺体模进行标准乳腺摄影来获取ESAK测量值。器官剂量转换系数（CF）确定为PMMA体模在特定深度处的空气比释动能与表面处空气比释动能的比值，并乘以组织与空气的质量能量吸收系数之比。使用RANDO体模通过将CF和ESAK值相乘来计算归一化的晶状体和甲状腺剂量。在W/Rh光谱中，OSLD对DBT系统散射辐射的响应最大变化为33%，并且观察到CM和TM之间散射剂量分布存在差异。晶状体和甲状腺的CF值分别在0.58至0.66和0.29至0.33之间。对于两眼单侧成像，晶状体的平均器官剂量在CM模式下为0.24 μGy/mAs，在TM模式下为0.18 μGy/mAs；甲状腺的平均器官剂量在CM模式下为0.24 μGy/mAs，在TM模式下为0.25 μGy/mAs。与CM相比，TM期间观察到更高的器官剂量，因为自动曝光控制（AEC）系统导致TM中的总mAs值更大。
