Jentzen Walter, Verschure Femke, van Zon Annelie, van de Kolk Rudie, Wierts Roel, Schmitz Jochen, Bockisch Andreas, Binse Ina
Klinik für Nuklearmedizin, Universität Duisburg-Essen, Essen, Germany
Fontys University of Applied Sciences, Eindhoven, The Netherlands; and.
J Nucl Med. 2016 Oct;57(10):1499-1504. doi: 10.2967/jnumed.115.170571. Epub 2016 May 19.
Iodine-positive bone metastases (BMs) are often resistant after initial radioiodine therapy applying the standard-activity approach. A comprehensive lesion-based response study for BMs has not, to our knowledge, yet been performed. In this study, pretherapy and follow-up I PET/CT data on BMs from differentiated thyroid cancer patients were retrospectively analyzed to assess the relationship between absorbed dose (AD) of radiation and response after initial radioiodine treatment.
Before and after initial radioiodine therapy, patients underwent serial PET/CT scanning after administration of 20-40 MBq of I. The pretherapy PET data were used to segment BM volumes and to predict the average ADs after administration of dosimetry-guided I activity. The lower volume limit of determinability of the applied segmentation method was a sphere volume of 0.16 mL. This volume limit classified the BMs into known-volume and fixed-volume groups with their respective average and minimum ADs. Follow-up I and F-FDG PET/CT data after treatment were analyzed to assess lesion-based therapy response. Response rates at different AD thresholds were calculated and were expressed as the percentage of completely responding BMs above the respective AD threshold. BMs with a maximum extent greater than twice the PET spatial resolution were visually scored for nonuniformity.
In total, 61 BMs in 10 patients were included, of which 46 and 15 comprised the known-volume group and the fixed-volume group, respectively. The median follow-up time was 5.6 mo (range, 3.7-23.2 mo). The median average and median minimum ADs in therapy were 183 Gy (range, 39-3,600 Gy) and 270 Gy (range, 63-1,300 Gy), respectively. A range of response rate of 70%-80% was achieved at an AD threshold range of 350-650 Gy. There were 26 BMs that were amenable to visual assessment of nonuniformity, of which two thirds (17/26) were scored as clearly nonuniform, and the majority (11/17) of these nonuniform BMs responded incompletely.
Both the high AD threshold associated with high response rates and the low median AD per unit of I activity elucidate the difficulty in achieving therapeutic efficacy for BMs when a single standard activity is administered. The relatively high AD threshold range is possibly a result of distinct levels of spatial nonuniformity in ADs.
碘阳性骨转移瘤（BMs）在采用标准活度方法进行初始放射性碘治疗后通常具有抗性。据我们所知，尚未对BMs进行基于病变的全面反应研究。在本研究中，对分化型甲状腺癌患者BMs的治疗前和随访I PET/CT数据进行回顾性分析，以评估辐射吸收剂量（AD）与初始放射性碘治疗后反应之间的关系。
在初始放射性碘治疗前后，患者在给予20 - 40 MBq的I后进行系列PET/CT扫描。治疗前PET数据用于分割BM体积，并预测剂量引导I活度给药后的平均ADs。所应用分割方法的可测定体积下限为0.16 mL的球体体积。该体积下限将BMs分为已知体积组和固定体积组，并分别给出其平均和最小ADs。分析治疗后的随访I和F - FDG PET/CT数据以评估基于病变的治疗反应。计算不同AD阈值下的反应率，并表示为高于各自AD阈值的完全反应BMs的百分比。对最大范围大于PET空间分辨率两倍的BMs进行不均匀性视觉评分。
总共纳入了10例患者的61个BMs，其中46个和15个分别构成已知体积组和固定体积组。中位随访时间为5.6个月（范围3.7 - 23.2个月）。治疗中的中位平均AD和中位最小AD分别为183 Gy（范围39 - 3600 Gy）和270 Gy（范围63 - 1300 Gy）。在350 - 650 Gy的AD阈值范围内，反应率达到70% - 80%。有26个BMs适合进行不均匀性视觉评估，其中三分之二（17/26）被评为明显不均匀，并且这些不均匀BMs中的大多数（11/17）反应不完全。
与高反应率相关的高AD阈值以及每单位I活度的低中位AD都说明了当给予单一标准活度时，实现BMs治疗效果的困难。相对较高的AD阈值范围可能是由于ADs中不同程度的空间不均匀性导致的。
