Feasibility and accuracy of single time point imaging for renal dosimetry following 177Lu-DOTATATE (‘Lutate’) therapy

Abstract

BackgroundThis study aims to assess both feasibility and accuracy of renal dosimetry imaging protocols in patients receiving Lutate therapy for neuroendocrine tumours (NETs), when data acquisition over multiple days is not possible on all cycles.MethodPatients who had received a full 4 cycles of Lutate therapy with complete imaging at each cycle were included. Imaging consisted of quantitative SPECT/CT of the kidneys at 4, 24 and 96–120 h post injection. Renal absorbed dose was calculated for each data set, and in addition, five alternative methods were explored for comparison. Method 1: a patient average clearance time (t1/2 average) derived from the first half of contributing patient data was used to estimate absorbed dose for subsequent patients based on 4 h imaging alone; method 2: t1/2 average was applied to subsequent patients on 24 h imaging alone; method 3: a patient-specific clearance rate (t1/2 patient) was determined from complete image data of cycle 1 and applied subsequently to remaining cycles using 4 h image data alone; method 4: t1/2 patient was applied to 24 h imaging alone in subsequent cycles; method 5: the 120 h data was estimated on subsequent cycles based on the cycle 1 fraction of injected activity (%IA) at 24 and 120 h.ResultsTwenty treatments from 18 patients, resulting in 80 cycles of therapy, were analysed. The measured average renal absorbed dose per cycle of treatment was 0.38 ± 0.19 Gy/GBq when derived from full imaging data. The use of t1/2 average applied to a single time point led to large deviations of dose estimates from true values (on average 59% and 30%, when using 4 h data and 24 h data, respectively). The use of complete image data on cycle 1 and the derivation of t1/2 patient led to improved dose estimates, with an average deviation from true values of 13% and 2% when using 4 h data only and 24 h data only, respectively. The use of a 120 h %IA derived from cycle 1 led to an average deviation from true dose estimates of 14%.ConclusionIn instances where demands on both patients and facilities make multiple time point data acquisition impractical, renal dosimetry is best derived through complete imaging at cycle 1 only followed by a single 24 h imaging time point on subsequent cycles, assuming no significant changes in renal function during the time course of therapy.

The Effect of Calibration Factors and Recovery Coefficients on 177Lu SPECT Activity Quantification Accuracy: A Monte Carlo Study

“…Spherical volumes corresponding to the physical sizes of the spheres were used to delineate all the spheres. This method of delineation is analogous to the use of CT images for segmentation of quantitative SPECT images [15,52,53]. Due to the irregular shape of the kidney, a 3D-isocontour threshold method was used to delineate the kidney volumes.…”

Dosimetry after peptide receptor radionuclide therapy: impact of reduced number of post-treatment studies on absorbed dose calculation and on patient management

“…The code takes as input data the output file of the GE DTK software including the volume and the activity concentrations in each drawn VOIs and at each time point. The code then performs mono-exponential curves fitting (from multiple time points after the first cycle and from a single time point for the following cycles, assuming no changes in the effective half-life for organs and tumors of interest [25,26]), numerical integrations, and dosimetry calculation. Radiationabsorbed doses by the tumors were computed using the method proposed by Sandström et al [23] where self-doses only are taken into account.…”

“…Alternatives for reducing the number of post-treatment scans have been investigated. Willowson et al [26] showed that the use of an average kidney effective half-life leads to a minimum mean relative error of 30% in the absorbed dose estimation. This error is much higher than the deviations presented in this paper.…”

“…Following the EANM/MIRD guidelines [22], three SPECT/CT studies, at t 1 = 24 h, t 2 = 96 h, and t 3 = 168 h are acquired after the first cycle of treatment in order to model the source organ/tumor distribution. For the following cycles, only a single SPECT/CT study at t = 24 h is necessary assuming an unchanged effective half-life of [ 177 Lu]-DOTA-TATE [25,26], a good example of tradeoff between feasibility and desirable accuracy.…”

“…With the intention to avoid patients returning to the hospital several times following the [ 177 Lu]-DOTA-TATE injection for several post-treatment scans, different methods have been suggested in the literature. A recent study by Willowson et al [26] investigated the feasibility of reliable renal dosimetry using a single time point imaging from the second cycle of treatment, as proposed before by Garske et al [25], or even from the first treatment cycle assuming an average patient effective half-life. Hänscheid et al [27] showed that the use of a single SPECT/CT acquired 4 days after injection was sufficient to derive reliable renal-absorbed dose estimates.…”