Department of Nuclear Medicine, West China Hospital, Sichuan University, Chengdu, China.
Med Phys. 2011 Oct;38(10):5412-9. doi: 10.1118/1.3602459.
The present study was conducted to investigate salivary iodine kinetics and dosimetry during repeated courses of radioiodine ((131)I) therapy for differentiated thyroid cancer (DTC). Such data could provide a better understanding of the mechanisms of (131)I induced salivary toxicity and help to develop appropriate methods to reduce this injury.
Seventy-eight consecutive DTC patients (mean age 45 ± 17 years, 60%, female) undergoing (131)I therapy for remnant ablation or metastatic tumors were prospectively recruited. Planar quantitative scintigraphy of head-neck images was serially acquired after administration of 2.9-7.4 GBq of (131)I to assess kinetics in the salivary glands of patients. Salivary absorbed doses were calculated based on the schema of Medical Internal Radiation Dosimetry.
The maximum uptakes in percentage of administered (131)I activity per kilogram of gland tissue (%/kg) were 12.9% ± 6.5%/kg (range, 0.4%-37.3%/kg) and 12.3% ± 6.2%/kg (range, 0.4%-35.1%/kg) for the parotid and submandibular glands, respectively. Statistically significant correlations of maximum uptake versus cumulative activity (r = -0.74, P < 0.01, for the parotid glands; r = -0.71, P < 0.01, for the submandibular glands) and treatment cycle (P < 0.001, for both gland types) were found. The effective half-lives of (131)I in the parotid and submandibular glands were 9.3 ± 3.5 h (range, 1.5-19.8 h) and 8.6 ± 3.2 h (range, 0.8-18.0 h), respectively. A statistically significant correlation was observed between effective half-life with cumulative activity (r = 0.37, P < 0.01) and treatment cycle (P = 0.03) only for the parotid glands. The calculated absorbed doses were 0.20 ± 0.10 mGy/MBq (range, 0.01-0.92 mGy/MBq) and 0.25 ± 0.09 mGy/MBq (range, 0.01-1.52 mGy/MBq) for the parotid and submandibular glands, respectively. The photon contribution to the salivary absorbed dose was minimal in relation to the beta dose contribution. Photon-absorbed dose fractions of total absorbed dose were 4.9% ± 1.3% (range, 1.1%-8.7%) and 3.7% ± 2.5% (range, 0.8%-7.9%) for the parotid and submandibular glands, respectively.
The iodine uptake of salivary glands is continuously reduced during the courses of therapy. The phenomenon of hyper-radiosensitivity may to some extent account for the occurrence of salivary gland hypofunction at very low radiation doses with low dose rates in (131)I therapy. On the other hand, failure to incorporate a nonuniform and preferential uptake by salivary gland ductal cells may result in underestimating the actual dose for the critical tissue. Other methods, including (124)I voxel-based dosimetry, are warranted to further investigate the (131)I-induced salivary gland toxicity.
本研究旨在探讨分化型甲状腺癌（DTC）患者接受多次放射性碘（131I）治疗期间唾液碘动力学和剂量学。此类数据可帮助我们更好地理解 131I 诱导唾液毒性的机制，并有助于开发减少这种损伤的适当方法。
连续招募 78 例接受 131I 治疗残余病灶或转移灶的 DTC 患者（平均年龄 45±17 岁，60%为女性）。治疗后，通过头颈部图像平面定量闪烁扫描，评估患者唾液腺的动力学。基于医学内部辐射剂量学方案，计算唾液吸收剂量。
每公斤腺体组织摄取的放射性碘活度百分比（%/kg）的最大值分别为 12.9%±6.5%/kg（范围，0.4%-37.3%/kg）和 12.3%±6.2%/kg（范围，0.4%-35.1%/kg），用于腮腺和颌下腺。发现最大摄取量与累积活度（r=-0.74，P<0.01，腮腺；r=-0.71，P<0.01，颌下腺）和治疗周期（P<0.001，两种腺体类型）呈显著相关。腮腺和颌下腺 131I 的有效半衰期分别为 9.3±3.5 小时（范围，1.5-19.8 小时）和 8.6±3.2 小时（范围，0.8-18.0 小时）。仅在腮腺中，有效半衰期与累积活度（r=0.37，P<0.01）和治疗周期（P=0.03）之间存在显著相关性。腮腺和颌下腺的唾液吸收剂量分别为 0.20±0.10 mGy/MBq（范围，0.01-0.92 mGy/MBq）和 0.25±0.09 mGy/MBq（范围，0.01-1.52 mGy/MBq）。光子对唾液吸收剂量的贡献相对于β剂量贡献是最小的。光子吸收剂量在总吸收剂量中的分数分别为 4.9%±1.3%（范围，1.1%-8.7%）和 3.7%±2.5%（范围，0.8%-7.9%），用于腮腺和颌下腺。
在治疗过程中，唾液腺对碘的摄取不断减少。超放射性敏感性现象在 131I 治疗中以低剂量率产生非常低的辐射剂量时，可能在一定程度上导致唾液腺功能低下。另一方面，未能纳入唾液腺导管细胞的非均匀和优先摄取可能导致对关键组织的实际剂量估计不足。需要其他方法，包括 124I 体素剂量学，以进一步研究 131I 诱导的唾液腺毒性。
