Abstract
BackgroundDosimetry is of high importance for optimization of patient-individual PSMA-targeted radioligand therapy (PSMA-RLT). The aim of our study was to evaluate and compare the feasibility of different approaches of image-based absorbed dose estimation in terms of accuracy and effort in clinical routine.MethodsWhole-body planar images and SPECT/CT images were acquired from 24 patients and 65 cycles at 24h, 48h, and ≥96h after administration of a mean activity of 6.4 GBq [177Lu]Lu-PSMA-617 (range 3–10.9 GBq). Dosimetry was performed by use of the following approaches: 2D planar-based dosimetry, 3D SPECT/CT-based dosimetry, and hybrid dosimetry combining 2D and 3D data. Absorbed doses were calculated according to IDAC 2.1 for the kidneys, the liver, the salivary glands, and bone metastases.ResultsMean absorbed doses estimated by 3D dosimetry (the reference method) were 0.54 ± 0.28 Gy/GBq for the kidneys, 0.10 ± 0.05 Gy/GBq for the liver, 0.81 ± 0.34 Gy/GBq for the parotid gland, 0.72 ± 0.39 Gy/GBq for the submandibular gland, and 1.68 ± 1.32 Gy/GBq for bone metastases. Absorbed doses of normal organs estimated by hybrid dosimetry showed small, non-significant differences (median up to 4.0%) to the results of 3D dosimetry. Using 2D dosimetry, in contrast, significant differences (median up to 10.9%) were observed. Regarding bone metastases, small, but significant differences (median up to 7.0%) of absorbed dose were found for both, 2D dosimetry and hybrid dosimetry. Bland-Altman analysis revealed high agreement between hybrid dosimetry and 3D dosimetry for normal organs and bone metastases, but substantial differences between 2D dosimetry and 3D dosimetry.ConclusionHybrid dosimetry provides high accuracy in estimation of absorbed dose in comparison to 3D dosimetry for all important organs and is therefore feasible for use in individualized PSMA-RLT.
Highlights
Prostate carcinoma is one of the most malignant diseases in men [1]
The aim of the present study was to compare absorbed dose values determined with altogether three dosimetry approaches, 2D planar-based dosimetry, 3D SPECT/CT-based dosimetry, and hybrid dosimetry combining planar scintigraphy and SPECT/CT, and to evaluate whether the accuracy of the hybrid method is suitable for use in clinical routine
The use of hybrid dosimetry resulted in only slight underestimation of the dose to the kidneys as well as slight overestimation of the dose to the liver and the salivary glands (Table 3)
Summary
Prostate carcinoma is one of the most malignant diseases in men [1]. A significant number of patients with prostate carcinoma progresses to the metastatic castration-resistant stage of prostate carcinoma (mCRPC) [2, 3]. There is physiological expression of PSMA in normal organs such as the kidneys, the liver, and the salivary glands [13,14,15], resulting in undesired irradiation of these organs This may cause radiotoxicity in the kidneys and salivary glands, probably leading to renal failure and xerostomia, respectively, and limiting the accumulative therapy doses and the number of therapy cycles. Hybrid dosimetry combining planar and SPECT/CT imaging was proposed as a valuable approach in dosimetry of peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors. This method offers a simplification in terms of image acquisition but maintaining the required accuracy in calculated absorbed dose results [23]. The aim of our study was to evaluate and compare the feasibility of different approaches of image-based absorbed dose estimation in terms of accuracy and effort in clinical routine
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