İstanbul Medical Journal (May 2024)
Determination of Optimum Imaging Numbers for 177Lu-PSMA Radionuclide Treatment Dosimetric Calculation
Abstract
Introduction: Lutetium-177 (177Lu) prostate-specific membrane antigen (PSMA) was first applied for treating castration-resistant prostate cancer (CRPC) in 2015, and PSA changes, low side effects, and good responses have been reported in the literature. Dosimetric calculations are required to determine the optimum number of treatments and prevent damage to critical organs. The aim of this study was to retrospectively investigate the feasibility of dosimetric calculations with fewer than four scans and to determine the most optimum imaging hours if dosimetric calculations can be performed with fewer than four scans. Methods: Whole body and single-photon emission computed tomography/computed tomography scans (4th hour, 24th hour, 48th hour and 96th hour) were performed on the patients after 177Lu-PSMA infusion. A comparison was made between doses calculated using four images, doses calculated using three images, and doses calculated using two images. The calculations were repeated with four images in nine configurations: 1st, 2nd, 3rd and 4th. Scan configurations were classified as C1-C9. C1 was accepted as the reference and evaluated statistically for significance research between other groups. Results: For an amount of 177Lu-PSMA activity of 3.7 GBq (100 mCi) per treatment, the mean kidney doses for C1, C2, C3, C4, C4, C5, C6, C7, C8, and C9 were calculated as 1.8±0.54 Gy, 1.83±0.57 Gy, 1.7±0.47 Gy, 1.91±0.57 Gy, 1.82±0.54 Gy, 1.59±0.47 Gy, 1.90±0.58 Gy, 1.82±0.57 Gy and 1.75±0.52 Gy, respectively. A significant difference was found in all groups among C2-C9 compared to C1. Conclusion: Optimum dosimetric calculations for treating CRPC should be performed with C5 (three images taken at the 4th, 24th and 48th hours) after 177Lu-PSMA injection. The error rate increases in calculations performed with a lower number of images.
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