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Abstract：
BACKGROUND: Internal dosimetry in individual patients is essential for safe and effective radioligand therapy. Multiple time point imaging for accurate dosimetry is time consuming and hence can be demanding for nuclear medicine departments as well as patients. The objectives of this study were (1) to assess absorbed doses to organs at risk and tumor lesions for [177Lu]Lu-PSMA-I&T using whole body SPECT imaging and (2) to investigate possible simplified dosimetry protocols.
METHODS: This study included 16 patients each treated with 4 cycles of [177Lu]Lu-PSMA-I&T. They underwent quantitative whole body SPECT/CT imaging (3 bed positions) at four time points (TP) comprising 2 h, 24 h, 48 h and 72-168 h post-injection (p.i.). Full 3D dosimetry (reference method) was performed for all patients and dose cycles for organs at risk (kidneys, parotid glands and submandibular glands) and up to ten tumor lesions per patient (resulting in 90 lesions overall). The simplified dosimetry methods (SM) included (1) generating time activity curves for subsequent cycles using a single TP of imaging applying the kinetics of dose cycle 1, and for organs at risk also (2) simple extrapolation from dose cycle 1 and (3) from both, dose cycle 1 and 2.
RESULTS: Normalized absorbed doses were 0.71 ± 0.32 mGy/MBq, 0.28 ± 0.12 mGy/MBq and 0.22 ± 0.08 mGy/MBq for kidneys, parotid glands and submandibular glands, respectively. Tumor doses decreased from 3.86 ± 3.38 mGy/MBq in dose cycle 1 to 2.01 ± 2.65 mGy/MBq in dose cycle 4. Compared to the full dosimetry approach the SM 1 using single TP imaging at 48 h p.i. resulted in the most accurate and precise results for the organs at risk in terms of absorbed doses per cycle and total cumulated dose. For tumor lesions better results were achieved using the fourth TP (≥ 72 h p.i.).
CONCLUSIONS: Simplification of safety dosimetry protocols is possible for [177Lu]Lu-PSMA-I&T therapy. If tumor dosimetry is of interest a later imaging TP (≥ 72 h p.i.) should be used/added to account for the slower kinetics of tumors compared to organs at risk.
METHODS: This study included 16 patients each treated with 4 cycles of [177Lu]Lu-PSMA-I&T. They underwent quantitative whole body SPECT/CT imaging (3 bed positions) at four time points (TP) comprising 2 h, 24 h, 48 h and 72-168 h post-injection (p.i.). Full 3D dosimetry (reference method) was performed for all patients and dose cycles for organs at risk (kidneys, parotid glands and submandibular glands) and up to ten tumor lesions per patient (resulting in 90 lesions overall). The simplified dosimetry methods (SM) included (1) generating time activity curves for subsequent cycles using a single TP of imaging applying the kinetics of dose cycle 1, and for organs at risk also (2) simple extrapolation from dose cycle 1 and (3) from both, dose cycle 1 and 2.
RESULTS: Normalized absorbed doses were 0.71 ± 0.32 mGy/MBq, 0.28 ± 0.12 mGy/MBq and 0.22 ± 0.08 mGy/MBq for kidneys, parotid glands and submandibular glands, respectively. Tumor doses decreased from 3.86 ± 3.38 mGy/MBq in dose cycle 1 to 2.01 ± 2.65 mGy/MBq in dose cycle 4. Compared to the full dosimetry approach the SM 1 using single TP imaging at 48 h p.i. resulted in the most accurate and precise results for the organs at risk in terms of absorbed doses per cycle and total cumulated dose. For tumor lesions better results were achieved using the fourth TP (≥ 72 h p.i.).
CONCLUSIONS: Simplification of safety dosimetry protocols is possible for [177Lu]Lu-PSMA-I&T therapy. If tumor dosimetry is of interest a later imaging TP (≥ 72 h p.i.) should be used/added to account for the slower kinetics of tumors compared to organs at risk.
摘要：
背景：个别患者的内部剂量测定对于安全有效的放射性配体治疗至关重要。用于精确剂量测定的多个时间点成像是耗时的,并且因此对于核医学部门以及患者可能是有要求的。这项研究的目的是（1）使用全身SPECT成像评估[177Lu]Lu-PSMA-I＆T对危险器官和肿瘤病变的吸收剂量；（2）研究可能的简化剂量学方案。
方法：本研究纳入16例患者，各接受4个周期的[177Lu]Lu-PSMA-I&T。他们在四个时间点（TP）接受了定量全身SPECT/CT成像（3个床位），包括2小时，24h,48小时和72-168小时后注射（p.i.）。对所有患者进行了全3D剂量测定（参考方法），并对有风险的器官（肾脏，腮腺和颌下腺）以及每位患者多达10个肿瘤病变（总共90个病变）。简化的剂量测定方法（SM）包括（1）使用单个TP成像应用剂量周期1的动力学生成后续周期的时间活动曲线，以及（2）从剂量周期1和（3）从两个，剂量周期1和2。
结果：归一化吸收剂量为0.71±0.32mGy/MBq，肾脏为0.28±0.12mGy/MBq和0.22±0.08mGy/MBq，腮腺和颌下腺，分别。肿瘤剂量从剂量周期1的3.86±3.38mGy/MBq下降到剂量周期4的2.01±2.65mGy/MBq。与全剂量测定方法相比，在48hp.i.时使用单TP成像的SM1在每个周期的吸收剂量和总累积剂量方面对处于危险中的器官产生了最准确和精确的结果。对于肿瘤病变，使用第四TP（≥72hp.i.）可获得更好的结果。
结论：简化[177Lu]Lu-PSMA-I&T治疗的安全剂量学方案是可能的。如果对肿瘤剂量测定感兴趣，则应使用/添加较晚的成像TP（≥72小时p.i.），以说明与有风险的器官相比，肿瘤的动力学较慢。
方法：本研究纳入16例患者，各接受4个周期的[177Lu]Lu-PSMA-I&T。他们在四个时间点（TP）接受了定量全身SPECT/CT成像（3个床位），包括2小时，24h,48小时和72-168小时后注射（p.i.）。对所有患者进行了全3D剂量测定（参考方法），并对有风险的器官（肾脏，腮腺和颌下腺）以及每位患者多达10个肿瘤病变（总共90个病变）。简化的剂量测定方法（SM）包括（1）使用单个TP成像应用剂量周期1的动力学生成后续周期的时间活动曲线，以及（2）从剂量周期1和（3）从两个，剂量周期1和2。
结果：归一化吸收剂量为0.71±0.32mGy/MBq，肾脏为0.28±0.12mGy/MBq和0.22±0.08mGy/MBq，腮腺和颌下腺，分别。肿瘤剂量从剂量周期1的3.86±3.38mGy/MBq下降到剂量周期4的2.01±2.65mGy/MBq。与全剂量测定方法相比，在48hp.i.时使用单TP成像的SM1在每个周期的吸收剂量和总累积剂量方面对处于危险中的器官产生了最准确和精确的结果。对于肿瘤病变，使用第四TP（≥72hp.i.）可获得更好的结果。
结论：简化[177Lu]Lu-PSMA-I&T治疗的安全剂量学方案是可能的。如果对肿瘤剂量测定感兴趣，则应使用/添加较晚的成像TP（≥72小时p.i.），以说明与有风险的器官相比，肿瘤的动力学较慢。
