Zachary Ells, Linus Hempel, Julia Ells, Muyu Wu, Maximilian Scheifele, Magdalena Schoell, Sophie C Siegmund, Mathias Zacherl, Rudolf A Werner, Jeremie Calais, Magnus Dahlbom, Guido Böning, Adrien Holzgreve, Astrid Delker, Lena M Unterrainer
The AD/GBq across the disease burden, individual lesions, and kidney remained comparable even with increased injected activity. No evidence of the tumor sink effect was found. No evidence of a clinically relevant tumor sink effect in patients with <2000 mL tumor volume was found but patients with substantially high TTV (> 2 L) lacks.
INTRODUCTION: Administration activities of 177Lu-PSMA were chosen cautiously in the treatment of advanced prostate cancer. The primary aim was to investigate the association between increased injected activities, and the calculated absorbed doses (AD).
METHODS: In this single center, retrospective analysis, patients with PSMA-avid metastatic castration-resistant prostate cancer treated with [177Lu]Lu-PSMA-I&T were included. Patients underwent multiple timepoint SPECT/CT imaging at 24, 48, and 72 h post-injection. Patients included were injected with 7.4, or 9.1 GBq. Segmentations were completed manually for the kidneys (CT-based), while a 3.0 SUV threshold-based approach was used for lesions. Dosimetry calculations were then performed using a multiple-timepoint protocol. Manual verification of the individual segmentations coregistered between timepoints was completed. All time activity data was fit using a mono-exponential function. Time-integrated activity was then convolved with voxel-s-value using a predefined 177Lu kernel resulting the AD in Gy. No further partial volume corrections were made.
RESULTS: 76 patients treated were included: 22 and 54 were injected with 9.1 ± 0.3 and 7.4 ± 0.3 GBq respectively. The AD/GBq to the kidney was comparable, 0.29 ± 0.08 vs. 0.33 ± 0.13 Gy/GBq [p=0.193] (9.1 vs. 7.4 GBq). The tumor AD/GBq was comparable between 9.1 and 7.4 GBq cohorts: total tumor burden (0.95 ± 0.42 vs. 0.92 ± 0.52 Gy/GBq) [p=0.302]; bone lesions 0.78 ± 0.42 vs. 0.74 ± 0.46 Gy/GBq [p=<0.001]; hottest lesion in each patient 1.37 ± 0.61 vs. 1.30 ± 0.74 [p=0.421]; coldest lesion in each patient 0.40 ± 0.16 vs. 0.50 ± 0.32 Gy/GBq [p=0.930].
CONCLUSION: The AD/GBq across the disease burden, individual lesions, and kidney remained comparable even with increased injected activity. No evidence of the tumor sink effect was found. No evidence of a clinically relevant tumor sink effect in patients with <2000 mL tumor volume was found but patients with substantially high TTV (> 2 L) lacks.