【正文】 標 Ideal World …. 理想狀態(tài) … ? Radiation delivered only to the imaged volume 輻射僅涵蓋成像部分 5 mm 0 + 5 mm Peak dose = “dose” Real World …. 現(xiàn)實情況 … ? Radiation distribution crosses the imaged volume 輻射跨越成像區(qū)域 5 mm 0 + 5 mm Peak dose “Tails” of dose distribution 劑量分布尾跡 Computed Tomography Dose Index ( CTDI ) CT劑量指數(shù)（ CTDI） ? Integral under ONE radiation dose profile 在單一劑量曲線下積分 ? Dose profile has very long ―tails‖ 劑量曲線有很長的尾跡 ? FDA uses finite integration limits (177。 7 T) FDA使用定積分極限（ 177。 optimize 知曉，理解和優(yōu)化 CTDImax , CTDIvol, DLP, and E ? Reference doses had positive effect in UK, used as part of the ACR accreditation process in the US 在英國，參考劑量具有積極的效果；在美國，它被應用于認證過程 ? Use effective dose to assess relative risk 應用有效劑量評估風險 Summary 總述 ? CT: large percentage of the medical collective dose to population CT: 對人群使用醫(yī)療檢查劑量的高百分比 ? Prudent response: Apply ALARA principles 審慎響應：使用 ALARA原則 ? CT Automatic Exposure Control a long overdue product is now available on new scanners makes dose calculations more difficult. CT dose worthy of closer attention CT自動曝光控制 —一個姍姍來遲的、應用于新掃描儀的產(chǎn)品 —使得劑量計算更困難。T ? CTDIw I PITCH = table index per rotation total nominal scan width CTDIvol = 1 ? CTDIw pitch estimate of average patient dose 平均病人劑量的估算值 measurement from one axial scan 來自軸向掃描的測量值 When a patient asks … ―What is my dose‖ they typically mean ―What is my risk‖ 當病人說“我的劑量是多少？”時， 其實他們在問“我承受了多大風險？” ? Biological injury includes 生物傷害包括 ? deterministic effects (skin burns, cataract formation) 確定效應（皮膚灼傷，白內(nèi)障形成） ? stochastic effects (cancer induction, geic effects) 隨機效應（癌癥的誘發(fā)，遺傳效應） ? Risk estimates are derived from 風險評估來源于 ? atomic bomb survivor data, other exposed groups 原子彈生存者的數(shù)據(jù)，其它暴露人群 ? Risk estimates are dependent on 風險評估有賴于 ? an dose and type, age, gender, reproductive status 器官劑量和類型，年齡，性別，生殖狀態(tài) ? an doses depend on patient size 器官劑量有賴于病人的身高與體重 Risk ? Biological Injury 風險 =生物傷害 What‘s the dose from an abdominal CT scan? 腹部 CT掃描的劑量？ Radiation Absorbed Dose (rad) Energy (100 ergs) Mass (1 gram) = What‘s the dose from an abdominal CT scan? 腹部 CT掃描的劑量？ ? Intuitively, we understand that the biologic risk from 20 CT slices is greater than from 10 CT slices. 直覺上，我們認為 20層 CT掃描的危害大于 10層掃描 ? If the average dose is 2 rad for 10 slices, what is the dose for 20 slices? 如果 10層 CT掃描的劑量是 2 rad， 20層的劑量是多少哪？ MSADw = 2 rad ten 1cm slices MSADw STILL = 2 rad twenty 1cm slices So how do we represent the greater biologic risk? 因此，我們?nèi)绾蚊枋鲚^嚴重的生物風險哪？ Integral dose 累計計量 ? Average dose ? slices = integral dose 平均計量乘以層數(shù)等于累計計量 ? But, dose and integral dose have same units (leads to confusion) and is not specific enough (doesn‘t reflect the difference between 1 or 10 mm slices) 但是，劑量和累計劑量具有相同的單位，而且并不明確 ? Better concept …. 更好的概念 … Dose Length Product (DLP) 劑量長度積 ? Represents integrated dose in terms of total scan length ( slices ? slice width) 代表了總掃描路徑中的累計劑量（層數(shù)乘以層厚） ? Related to energy imparted but more intuitive than using energy units (Joules) 涉及應用的能量，但與使用能量單位相比更直觀 ? Required in Europe, migrating to US 歐洲要求使用，后被美國采用 ? DLP = CTDIvol (mGy) ? scan length (cm) So, DLP represent the greater biologic risk! 所以， DLP代表了更高的生物風險！ DLP = 20 rad?cm DLP = 40 rad?cm CTDIvol = 2 rad ten 1cm slices CTDIvol STILL = 2 rad twenty 1cm slices SI units (1 rad = 10 mGy) 國際單位 (1 rad = 10 mGy) DLP: 20 mGy ? 20 cm = 400 mGy?cm DLP g