Koral K F, Dewaraja Y, Li J, Barrett C L, Regan D D, Zasadny K R, Rommelfanger S G, Francis I R, Kaminski M S, Wahl R L
Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109-0028, USA.
J Nucl Med. 2000 Sep;41(9):1579-86.
A study of the use of 131I-labeled anti-B1 monoclonal antibody, proceeded by an unlabeled predose, for therapy of previously untreated non-Hodgkin's lymphoma patients has recently been completed at the University of Michigan, Ann Arbor. More than half of the patients treated were imaged intratherapy with SPECT to separate apparently large tumors, unresolved by conjugate views, into individual ones specified by CT scan. The dosimetry of these tumors is reported here.
The activity-quantification procedure used 3-dimensional CT-to-SPECT fusion so that attenuation maps could be computed from CT and that volumes of interest could be drawn on the CT slices and transferred to the SPECT images. Daily conjugate-view images after a tracer dose of labeled anti-B1 antibody followed by an unlabeled predose provided the shape of the time-activity curve for the calculation of therapy dosimetry. Reconstructed SPECT counts that were within a volume of interest were converted to activity by using a background-and-radius-adaptive conversion factor. Activities were increased for tumors less than 200 g using a recovery-coefficient factor derived from activity measurements for a set of spheres with volumes ranging from 1.6 to 200 cm3. The calculated tumor radiation absorbed dose was based, in part, on the CT volume and on the intratherapy-SPECT activity.
The mean of the radiation dose values for 131 abdominal or pelvic tumors in 31 patients was 616 cGy with a standard deviation of +/- 50 cGy. The largest dose was 40 Gy and the smallest dose was 73 cGy. The mean volume for the tumors was 59.2 +/- 11.2 cm3. The correlation coefficient between absorbed dose and tumor volume was small (r2 = 0.007), and the slope of the least-squares fit represented a decrease of only 36.4 cGy per 100 cm3 increase in volume. This small slope may reflect a characteristic of anti-B1 antibody therapy that is important for its success. The mean absorbed dose per unit administered activity was 1.83 +/- 0.145 Gy/GBq. The largest value was 12.6 Gy/GBq, and the smallest value was 0.149 Gy/GBq. The mean dose for 9 axillary tumors in 5 patients was significantly lower than the average dose for abdominal and pelvic tumors (P = 0.01). Therefore, axillary tumors should be grouped separately in assessing dose-response relationships. Anecdotal patient results tended to verify the validity of using the shape of the conjugate-view time-activity curve for the average SPECT-intratherapy curve. However, there was also an indication that the shape varies somewhat for individual tumors with respect to time to peak.
Hybrid SPECT-conjugate-view dosimetry provided radiation absorbed dose estimates for the individual patient tumors that were resolved by CT.
密歇根大学安娜堡分校最近完成了一项关于使用131I标记的抗B1单克隆抗体（在给予未标记的预剂量后）治疗先前未经治疗的非霍奇金淋巴瘤患者的研究。超过一半接受治疗的患者在治疗期间用SPECT进行成像，以将共轭视图无法分辨的明显大肿瘤分成CT扫描确定的单个肿瘤。本文报告了这些肿瘤的剂量测定情况。
活性定量程序使用三维CT到SPECT融合技术，以便能从CT计算衰减图，并能在CT切片上绘制感兴趣区并转移到SPECT图像上。给予标记抗B1抗体的示踪剂量后再给予未标记的预剂量，每日的共轭视图图像提供了时间-活性曲线的形状，用于计算治疗剂量测定。通过使用背景和半径自适应转换因子，将感兴趣区内重建的SPECT计数转换为活性。对于体积小于200 g的肿瘤，使用从一组体积范围为1.6至200 cm3的球体活性测量得出的恢复系数因子来增加活性。计算的肿瘤辐射吸收剂量部分基于CT体积和治疗期间SPECT活性。
31例患者中131个腹部或盆腔肿瘤的辐射剂量值平均为616 cGy，标准差为±50 cGy。最大剂量为40 Gy，最小剂量为73 cGy。肿瘤的平均体积为59.2±11.2 cm3。吸收剂量与肿瘤体积之间的相关系数较小（r2 = 0.007），最小二乘拟合的斜率表示体积每增加100 cm3仅减少36.4 cGy。这个小斜率可能反映了抗B1抗体治疗的一个对其成功很重要的特征。每单位给药活性的平均吸收剂量为1.83±0.145 Gy/GBq。最大值为12.6 Gy/GBq，最小值为0.149 Gy/GBq。5例患者中9个腋窝肿瘤的平均剂量显著低于腹部和盆腔肿瘤的平均剂量（P = 0.01）。因此，在评估剂量反应关系时，腋窝肿瘤应单独分组。个别患者的结果倾向于验证使用共轭视图时间-活性曲线形状作为平均SPECT治疗期间曲线的有效性。然而，也有迹象表明，个别肿瘤相对于达到峰值的时间，其形状有所不同。
SPECT与共轭视图混合剂量测定法为经CT分辨的个体患者肿瘤提供了辐射吸收剂量估计值。
