Improving quantitative dosimetry in 177Lu-DOTATATE SPECT by energy window-based scatter corrections

Abstract

PurposePatient-specific dosimetry of lutetium-177 (177Lu)-DOTATATE treatment in neuroendocrine tumours is important, because uptake differs across patients. Single photon emission computer tomography (SPECT)-based dosimetry requires a conversion factor between the obtained counts and the activity, which depends on the collimator type, the utilized energy windows and the applied scatter correction techniques. In this study, energy window subtraction-based scatter correction methods are compared experimentally and quantitatively.Materials and methods177Lu SPECT images of a phantom with known activity concentration ratio between the uniform background and filled hollow spheres were acquired for three different collimators: low-energy high resolution (LEHR), low-energy general purpose (LEGP) and medium-energy general purpose (MEGP). Counts were collected in several energy windows, and scatter correction was performed by applying different methods such as effective scatter source estimation (ESSE), triple-energy and dual-energy window, double-photopeak window and downscatter correction. The intensity ratio between the spheres and the background was measured and corrected for the partial volume effect and used to compare the performance of the methods.ResultsLow-energy collimators combined with 208 keV energy windows give rise to artefacts. For the 113 keV energy window, large differences were observed in the ratios for the spheres. For MEGP collimators with the ESSE correction technique, the measured ratio was close to the real ratio, and the differences between spheres were small.ConclusionFor quantitative 177Lu imaging MEGP collimators are advised. Both energy peaks can be utilized when the ESSE correction technique is applied. The difference between the calculated and the real ratio is less than 10% for both energy windows.

MIRD Pamphlet No. 26: Joint EANM/MIRD Guidelines for Quantitative 177Lu SPECT Applied for Dosimetry of Radiopharmaceutical Therapy

“…Better results are obtained when the scatter estimate is incorporated into the projector step in the iterative reconstruction algorithm. Additionally, because a ME collimator the scatter energy window set above the 208-keV photopeak usually contains relatively few counts, this second scatter window can be ignored (45,46).…”

“…Both the ESSE and the APDI methods have been successfully applied to 177 Lu phantoms studies (30,45).…”

“…Image reconstructions used OSEM algorithms with CDR compensation available on commercial cameras (46) or reconstruction methods developed in-house (30). All reconstructions used CT-based AC, whereas for scatter correction the dual-energy window method (DEW) (30,46), TEW (45,56), ESSE (45), and APDI (30) methods were investigated. Table 4 summarizes the results of these studies.…”

Accuracy of 177Lu activity quantification in SPECT imaging: a phantom study

“…Our group's previous 177 Lu quantification studies [13], based on the 113 keV photopeak using low-energy high-resolution (LEHR) collimator and the analytical photon distribution interpolated (APDI) scatter correction method [14, 15], resulted in 2% accuracy error for a 70 ml container scanned in air and in water (without background activity). In parallel, seven scatter correction methods and different collimators were evaluated by de Nijs et al [16] using phantom containing hot spheres in warm background with concentration ratio close to 13:1. Although triple energy window (TEW) [17] was found to not be suitable when imaging the 113 keV photopeak, for the 208 keV peak TEW, or even DEW method, resulted in activity estimation errors close to 10% for the largest 37 ml sphere.…”

Comparison of biological properties of [177Lu]Lu‐ProBOMB1 and [177Lu]Lu‐NeoBOMB1 for GRPR targeting

“…For instance, the estimated absorbed dose for pancreas was 3.0 × 10 −4 mGy/MBq compared with 0.282 mGy/MBq, which is almost 3 magnitudes higher. 20 Many radiopharmaceuticals have leveraged this pair to diagnose and treat malignancies, with prominent examples including [ 68 Ga]Ga/[ 177 Lu]Lu-DOTA-TATE and [ 68 Ga]Ga/[ 177 Lu]Lu-PSMA-617, currently used in clinical trials. Stability of [ 177 Lu]Lu-ProBOMB1 at the 5 minutes in vivo plasma stability was 85.6 ± 5.3% (n = 3).…”