Kao Yung Hsiang
Department of Nuclear Medicine, The Royal Melbourne Hospital, Australia.
Asia Ocean J Nucl Med Biol. 2023;11(2):158-167.
The traditional practice of empiric radioiodine (I-131) prescription is scientifically obsolete and inappropriate for inoperable metastatic differentiated thyroid cancer. However, theranostically guided prescription is still years away for many institutions. A personalized predictive method of radioiodine prescription that bridges the gap between empiric and theranostic methods is presented. It is an adaptation of the "maximum tolerated activity" method, where serial blood sampling is replaced by population kinetics carefully chosen by the user. It aims to maximize crossfire benefits within safety constraints to overcome tumour absorbed dose heterogeneity for a safe and effective first radioiodine fraction i.e., the First Strike.
The EANM method of blood dosimetry was incorporated with population kinetics, marrow and lung safety constraints, body habitus and clinical assessment of metastatic extent. Population data of whole body and blood kinetics in patients with and without metastases, prepared by recombinant human thyroid stimulating hormone or thyroid hormone withdrawal, and the maximum safe marrow dose rate were deduced from published data. For diffuse lung metastases, the lung safety limit was linearly scaled by height and separated into lung and remainder-of-body components.
The slowest whole body Time Integrated Activity Coefficient (TIAC) amongst patients with any metastases was 33.5±17.0 h and the highest percentage of whole body TIAC attributed to blood was 16.6±7.9%, prepared by thyroid hormone withdrawal. A variety of other average radioiodine kinetics is tabulated. Maximum safe marrow dose rate was deduced to be 0.265 Gy/h per fraction, where blood TIAC is normalised to administered activity. An easy-to-use calculator was developed which only requires height, weight and gender to populate recommendations for personalized First Strike prescription. The user decides by clinical gestalt whether the prescription is to be constrained by marrow or lung, then selects an activity depending on how extensive the metastases are likely to be. A Standard Female with oligometastasis and good urine output without diffuse lung metastasis is expected to safely tolerate 8.03 GBq of radioiodine as the First Strike.
This predictive method will help institutions rationalise the First Strike prescription based on radiobiologically sound principles, personalised to individual circumstances.
经验性放射性碘（I-131）处方的传统做法在科学上已过时，不适用于无法手术的转移性分化型甲状腺癌。然而，对许多机构来说，治疗诊断指导下的处方仍需数年时间。本文提出了一种个性化的放射性碘处方预测方法，该方法弥合了经验性方法和治疗诊断方法之间的差距。它是“最大耐受活度”方法的一种改进，用用户精心选择的群体动力学取代了连续血样采集。其目的是在安全限制范围内最大化交叉火力效益，以克服肿瘤吸收剂量的异质性，从而实现安全有效的首次放射性碘给药，即首次打击。
将欧洲核医学与分子影像协会（EANM）的血液剂量测定方法与群体动力学、骨髓和肺部安全限制、身体体型以及转移范围的临床评估相结合。通过重组人促甲状腺激素或甲状腺激素撤减制备的有转移和无转移患者的全身和血液动力学群体数据，以及最大安全骨髓剂量率，均从已发表的数据中推导得出。对于弥漫性肺转移，肺安全限值根据身高进行线性缩放，并分为肺部和身体其他部分。
在任何有转移的患者中，全身最慢的时间积分活度系数（TIAC）为33.5±17.0小时，通过甲状腺激素撤减制备的全身TIAC中归因于血液的最高百分比为16.6±7.9%。还列出了各种其他平均放射性碘动力学数据。推导得出最大安全骨髓剂量率为每分次0.265 Gy/h，其中血液TIAC根据给药活度进行归一化。开发了一个易于使用的计算器，只需输入身高、体重和性别，就能生成个性化首次打击处方的建议。用户根据临床判断决定处方是否受骨髓或肺部限制，然后根据转移可能的范围选择活度。预计一名无弥漫性肺转移、有寡转移且尿量良好的标准女性作为首次打击可安全耐受8.03 GBq的放射性碘。
这种预测方法将有助于各机构根据放射生物学合理原则，针对个体情况制定个性化的首次打击处方。
