Department of Physics, FFCLRP, University of São Paulo, Ribeirão Preto, Brazil.
Department of Medical Imaging, Haematology and Clinical Oncology, Ribeirão Preto Medical School, University of Sao Paulo, Brazil.
Phys Med Biol. 2021 Apr 16;66(8). doi: 10.1088/1361-6560/abe559.
Assessing the radiation doses received by patients in computed tomography is still challenging. To overcome this, the American Association of Physicists in Medicine has introduced the concept of the size specific dose estimate (SSDE). However, the calculation of SSDE for head CT scans requires the knowledge of attenuation characteristics of the volume scanned, making its implementation in the daily clinical workflow cumbersome. In this study, we defined conversion coefficients from CTDIto SSDE for head CT scans based solely on the age of the patient. Using the head circumference-for-age from the child growth standards of the World Health Organization (WHO), the effective diameter-for-age was calculated for male and female individuals from 0 to 60 months-old. The effective diameter was converted into a water equivalent diameter-for-age, using a correlation established from the measurements of both quantities in 295 exams of male and female patients, from 0 to 18 years-old. WHO-estimated water equivalent diameter-for-age was validated against the measured water equivalent diameter-for-age. The head circumference-for-age from WHO was extrapolated for male and females individuals up to 18 years-old and their respective water equivalent diameter were estimated. Finally, the SSDE was calculated for all the CT head scans performed in a 9-years period in patients aged from 0 to 18 years old. Typical values of CTDIand DLP were also defined. SSDE varied from 0.80 up to 1.16 of the CTDI, depending on sex and age of the patient. WHO-estimated water equivalent diameter-for-age differed less than 20% from the measured water equivalent diameter-for-age. Typical values of SSDE varied from 28.5 up to 38.9 mGy, while typical values ranged from 30.9 up to 47.6 mGy for the CTDIand from 417.6 up to 861.1 mGy*cm for the DLP. SSDE can be directly calculated for head CT scans once the age of the patient is known.
评估 CT 扫描中患者接受的辐射剂量仍然具有挑战性。为了解决这个问题，美国医学物理学家协会引入了体积剂量指数（CTDI）的概念。然而，对于头部 CT 扫描，计算体积剂量指数需要了解扫描体积的衰减特性，这使得它在日常临床工作流程中的实施变得繁琐。在这项研究中，我们仅根据患者的年龄定义了头部 CT 扫描的容积剂量指数到体积剂量指数转换系数。利用世界卫生组织（WHO）儿童生长标准中的头围年龄，计算了男性和女性个体从 0 到 60 个月的有效直径年龄。使用在 295 例男性和女性患者 0 至 18 岁的测量结果建立的相关性，将有效直径转换为与年龄对应的水等效直径。利用 WHO 测量的与年龄对应的水等效直径对与年龄对应的水等效直径进行了验证。对男性和女性个体的头围年龄进行了外推，直到 18 岁，并估计了他们各自的水等效直径。最后，计算了在 9 年期间 0 至 18 岁患者进行的所有头部 CT 扫描的体积剂量指数。还定义了典型的 CTDI 和剂量长度乘积（DLP）值。体积剂量指数取决于患者的性别和年龄，范围从 CTDI 的 0.80 到 1.16。与年龄对应的水等效直径的测量值相差不到 20%。体积剂量指数的典型值从 28.5 到 38.9 mGy 不等，而 CTDI 的典型值范围从 30.9 到 47.6 mGy，剂量长度乘积的典型值范围从 417.6 到 861.1 mGy*cm。一旦知道患者的年龄，就可以直接计算头部 CT 扫描的体积剂量指数。
