Year: 2021
Type: dissertation
Study design: Observational Study
Abstract: Dosimetry is a necessary process in radiation therapies to ensure required energy for effective treatment is transferred to the target while saving the healthy organs.Dosimetry using MIRD formalism has been used clinically but it has limitations as it is a population-based method.Voxel-level dosimetry methods have been developed to introduce patient-specificity to dosimetry, but are still mainly under research with a few commercial ready solutions to be applied for targeted radionuclide therapy (TRT).One of the significant applications of TRT is in treating mCRPC patients with 177 Lu-PSMA.Purpose: Estimating and comparing the absorbed doses of kidneys and liver for mCRPC patients post 177 Lu-PSMA therapy using MIRD and voxel-level dosimetry.Methods: 12 patients went through 1 to 5 cycles of 177 Lu-PSMA treatment and were imaged with SPECT-CT in Kuopio University Hospital at 4h, 24h and possibly 48h time points.Then, their kidney and liver doses were estimated using HERMES software.Results: Absorbed doses estimated with voxel-level dosimetry were higher than absorbed doses estimated with MIRD.The mean absorbed doses for kidneys and liver based on MIRD dosimetry were 3.29 and 0.219 Gy, respectively.Respective values based on voxel-level dosimetry were 7.91 and 0.869 Gy.The accumulative doses for all patients were within established tolerance limits for kidneys and liver.The highest kidney dose was determined for patient who had only one functional kidney.Conclusion: Absorbed doses estimated with voxel-level dosimetry were higher than the ones estimated with MIRD dosimetry mostly due to the difference in estimation of time activity curves (TACs).In voxel-level dosimetry software, a physical decay of the radioisotope was assumed after the final sampled activity point of the TAC, whereas biological decay was used in MIRD dosimetry.Thus, when using voxel-level dosimetry with the studied software, one should always image a late time point (e.g. 1 week after treatment) to estimate the true decay and extraction of 177 Lu from the body.
Author: Sajeda Majed Alawi
Language: English
Subfield: Radiology, Nuclear Medicine and Imaging
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W3183634224