Patient-specific dosimetry adapted to variable number of SPECT/CT time-points per cycle for $$^{177}$$Lu-DOTATATE therapy

Abstract

Background The number of SPECT/CT time-points is important for accurate patient dose estimation in peptide receptor radionuclide therapy. However, it may be limited by the patient’s health and logistical reasons. Here, an image-based dosimetric workflow adapted to the number of SPECT/CT acquisitions available throughout the treatment cycles was proposed, taking into account patient-specific pharmacokinetics and usable in clinic for all organs at risk. Methods Thirteen patients with neuroendocrine tumors were treated with four injections of 7.4 GBq of $$^{177}$$ 177 Lu-DOTATATE. Three SPECT/CT images were acquired during the first cycle (1H, 24H and 96H or 144H post-injection) and a single acquisition (24H) for following cycles. Absorbed doses were estimated for kidneys (LK and RK), liver (L), spleen (S), and three surrogates of bone marrow (L2 to L4, L1 to L5 and T9 to L5) that were compared. 3D dose rate distributions were computed with Monte Carlo simulations. Voxel dose rates were averaged at the organ level. The obtained Time Dose-Rate Curves (TDRC) were fitted with a tri-exponential model and time-integrated. This method modeled patient-specific uptake and clearance phases observed at cycle 1. Obtained fitting parameters were reused for the following cycles, scaled to the measure organ dose rate at 24H. An alternative methodology was proposed when some acquisitions were missing based on population average TDRC (named STP-Inter). Seven other patients with three SPECT/CT acquisitions at cycles 1 and 4 were included to estimate the uncertainty of the proposed methods. Results Absorbed doses (in Gy) per cycle available were: 3.1 ± 1.1 (LK), 3.4 ± 1.5 (RK), 4.5 ± 2.8 (L), 4.6 ± 1.8 (S), 0.3 ± 0.2 (bone marrow). There was a significant difference between bone marrow surrogates (L2 to L4 and L1 to L5, Wilcoxon’s test: p value < 0.05), and while depicting very doses, all three surrogates were significantly different than dose in background (p value < 0.01). At cycle 1, if the acquisition at 24H is missing and approximated, medians of percentages of dose difference (PDD) compared to the initial tri-exponential function were inferior to 3.3% for all organs. For cycles with one acquisition, the median errors were smaller with a late time-point. For STP-Inter, medians of PDD were inferior to 7.7% for all volumes, but it was shown to depend on the homogeneity of TDRC. Conclusion The proposed workflow allows the estimation of organ doses, including bone marrow, from a variable number of time-points acquisitions for patients treated with $$^{177}$$ 177 Lu-DOTATATE.

Dosimetric impact of 3D motion-compensated SPECT reconstruction for SIRT planning

“…A dosimetry workflow based on Monte Carlo simulations was adapted from [ 32 ] to estimate the average absorbed doses for all VOI from 3D and 3Dcomp reconstructions. 99m Tc SPECT images were normalized according to the injected activity by considering all detected counts in the liver and lungs VOIs.…”

“…For each SPECT, a 3D dose rate map was obtained and the mean of dose rates was computed for each VOI. The final absorbed dose per VOI was estimated by considering mono-exponential decay, with 90 Y half-life of 64 h. Statistical uncertainties of the Monte Carlo simulations were lower than 1% in all ROIs, and computation times were around 10 min [ 32 ].…”

Performance study of a 360° CZT camera for monitoring 177Lu-PSMA treatment

“…SPECT imaging is currently the only source of information for estimating absorbed dose after a patient's therapeutic dose injection. Quantification can be performed with 2D planar scintigraphy [8][9][10] or from 3D reconstructed images [11,12], the latter showing better accuracy [13]. More details about absorbed dose estimation from 3D SPECT images maybe found in [14,15].…”

Unintentional Intra-arterial Injection of 177Lu-PSMA-1 in a Patient With a Peritoneal Carcinosis Secondary to a Metastatic Prostate Cancer

“…The man did not experience any pain or redness in the forearm afterward. The left hand arm estimated that the absorbed dose obtained by Monte Carlo calculation 1 was 0.09 mGy/MBq, 20% higher than the controlateral arm. Inadvertent intra-arterial injection has already been described with different diagnostic radiopharmaceuticals, such as 99m Tc-MDP, 2,3 99m Tc-MIBI, 4 123 I-MIBG, 5 or 18 F-FDG, 6,7 without any serious interferences or adverse events.…”