Almeida P, Bendriem B, de Dreuille O, Peltier A, Perrot C, Brulon V
Service Hospitalier Frédéric Joliot, Département de Recherche Médicale, Orsay, France.
Eur J Nucl Med. 1998 Oct;25(10):1435-41. doi: 10.1007/s002590050320.
Quantification in positron emission tomography (PET) and single photon emission tomographic (SPET) relies on attenuation correction which is generally obtained with an additional transmission measurement. Therefore, the evaluation of the radiation doses received by patients needs to include the contribution of transmission procedures in SPET (SPET-TM) and PET (PET-TM). In this work we have measured these doses for both PET-TM and SPET-TM. PET-TM was performed on an ECAT EXACT HR+ (CTI/Siemens) equipped with three rod sources of germanium-68 (380 MBq total) and extended septa. SPET-TM was performed on a DST (SMV) equipped with two collimated line sources of gadolinium-153 (4 GBq total). Two anthropomorphic phantoms representing a human head and a human torso, were used to estimate the doses absorbed in typical cardiac and brain transmission studies. Measurements were made with thermoluminescent dosimeters (TLDs, consisting of lithium fluoride) having characteristics suitable for dosimetry investigations in nuclear medicine. Sets of TLDs were placed inside small plastic bags and then attached to different organs of the phantoms (at least two TLDs were assigned to a given organ). Before and after irradiation the TLDs were placed in a 2.5-cm-thick lead container to prevent exposure from occasional sources. Ambient radiation was monitored and taken into account in calculations. Transmission scans were performed for more than 12 h in each case to decrease statistical noise fluctuations. The doses absorbed by each organ were calculated by averaging the values obtained for each corresponding TLD. These values were used to evaluate the effective dose (ED) following guidelines described in ICRP report number 60. The estimated ED values for cardiac acquisitions were 7.7 x 10(-4) +/- 0.4 x 10(-4) mSv/MBq.h and 1.9 x 10(-6) +/- 0.4 x 10(-6) mSv/MBq.h for PET-TM and SPET-TM, respectively. For brain scans, the values of ED were calculated as 2.7 x 10(-4) +/- 0.2 x 10(-4) mSv/MBq.h for PET-TM and 5.2 x 10(-7) +/- 2.3 x 10(-7) mSv/MBq.h for SPET-TM. In our institution, PET-TM is usually performed for 15 min prior to emission. SPET-TM is performed simultaneously with emission and usually lasts 30 and 15 min for brain and cardiac acquisitions respectively. Under these conditions ED values, estimated for typical source activities at delivery time (22,000 MBq in SPET and 555 MBq for PET), were 1.1 x 10(-1) +/- 0.1 x 10(-1) mSv and 1.1 x 10(-2) +/- 0.2 x 10(-2) mSv for cardiac PET-TM and SPET-TM respectively. For brain acquisitions, the ED values obtained under the same conditions were 3.7 x 10(-2) +/- 0.3 x 10(-2) mSv and 5.8 x 10(-3) +/- 2.6 x 10(-3) mSv for PET-TM and SPET-TM respectively. These measurements show that the dose received by a patient during a transmission scan adds little to the typical dose received in a routine nuclear medicine procedure. Radiation dose, therefore, does not represent a limit to the generalised use of transmission measurements in clinical SPET or PET.
正电子发射断层扫描（PET）和单光子发射断层扫描（SPET）中的定量分析依赖于衰减校正，而衰减校正通常通过额外的透射测量来获得。因此，评估患者所接受的辐射剂量需要考虑SPET（SPET-TM）和PET（PET-TM）中透射程序的贡献。在本研究中，我们测量了PET-TM和SPET-TM的这些剂量。PET-TM在配备三个锗-68棒源（总计380 MBq）和扩展隔板的ECAT EXACT HR+（CTI/西门子）上进行。SPET-TM在配备两个准直钆-153线源（总计4 GBq）的DST（SMV）上进行。使用两个分别代表人类头部和躯干的人体模型来估计典型心脏和脑部透射研究中吸收的剂量。测量使用具有适合核医学剂量学研究特性的热释光剂量计（TLD，由氟化锂组成）进行。将TLD组放置在小塑料袋内，然后附着到人体模型的不同器官上（每个给定器官至少分配两个TLD）。照射前后，将TLD放置在一个2.5厘米厚的铅容器中，以防止受到偶然源的照射。监测环境辐射并在计算中予以考虑。每种情况下的透射扫描均进行超过12小时，以减少统计噪声波动。通过对每个相应TLD获得的值求平均值来计算每个器官吸收的剂量。这些值用于按照国际辐射防护委员会第60号报告中所述的指南评估有效剂量（ED）。心脏采集的估计ED值，PET-TM为7.7×10⁻⁴±0.4×10⁻⁴ mSv/MBq·h，SPET-TM为1.9×10⁻⁶±0.4×10⁻⁶ mSv/MBq·h。对于脑部扫描，PET-TM的ED值计算为2.7×10⁻⁴±0.2×10⁻⁴ mSv/MBq·h，SPET-TM为5.2×10⁻⁷±2.3×10⁻⁷ mSv/MBq·h。在我们机构，PET-TM通常在发射前进行15分钟。SPET-TM与发射同时进行，脑部采集通常持续30分钟，心脏采集持续15分钟。在这些条件下，针对交付时的典型源活度（SPET为22,000 MBq，PET为555 MBq）估计的ED值，心脏PET-TM和SPET-TM分别为1.1×10⁻¹±0.1×10⁻¹ mSv和1.1×10⁻²±0.2×10⁻² mSv。对于脑部采集，在相同条件下获得的PET-TM和SPET-TM的ED值分别为3.7×10⁻²±0.3×10⁻² mSv和5.8×10⁻³±2.6×10⁻³ mSv。这些测量结果表明，患者在透射扫描期间接受的剂量对常规核医学程序中接受的典型剂量贡献很小。因此，辐射剂量并不构成临床SPET或PET中广泛使用透射测量的限制。
