Internal dosimetry in F-18 FDG PET examinations based on long-time-measured organ activities using total-body PET/CT: does it make any difference from a short-time measurement?

Abstract

Purpose A 2-m axial field-of-view, total-body PET/CT scanner (uEXPLORER) has been recently developed to provide total-body coverage and ultra-high sensitivity, which together, enables opportunities for in vivo time-activity curve (TAC) measurement of all investigated organs simultaneously with high temporal resolution. This study aims at quantifying the cumulated activity and patient dose of 2-[F-18]fluoro-2-deoxy-D-glucose (F-18 FDG ) imaging by using delayed time-activity curves (TACs), measured out to 8-h post-injection, for different organs so that the comparison between quantifying approaches using short-time method (up to 75 min post-injection) or long-time method (up to 8 h post-injection) could be performed. Methods Organ TACs of 10 healthy volunteers were collected using total-body PET/CT in 4 periods after the intravenous injection of F-18 FDG. The 8-h post-injection TACs of 6 source organs were fitted using a spline method (based on Origin (version 8.1)). To compare with cumulated activity estimated from spline-fitted curves, the cumulated activity estimated from multi-exponential curve was also calculated. Exponential curve was fitted with shorter series of data consistent with clinical procedure and previous dosimetry works. An 8-h dynamic bladder wall dose model considering 2 voiding were employed to illustrate the differences in bladder wall dose caused by the different measurement durations. Organ absorbed doses were further estimated using Medical Internal Radiation Dose (MIRD) method and voxel phantoms. Results A short-time measurement could lead to significant bias in estimated cumulated activity for liver compared with long-time-measured spline fitted method, and the differences of cumulated activity were 18.38% on average. For the myocardium, the estimated cumulated activity difference was not statistically significant due to large variation in metabolism among individuals. The average residence time differences of brain, heart, kidney, liver, and lungs were 8.38%, 15.13%, 25.02%, 23.94%, and 16.50% between short-time and long-time methods. Regarding effective dose, the maximum differences of residence time between long-time-measured spline fitted curve and short-time-measured multi-exponential fitted curve was 9.93%. When using spline method, the bladder revealed the most difference in the effective dose among all the investigated organs with a bias up to 21.18%. The bladder wall dose calculated using a long-time dynamic model was 13.79% larger than the two-voiding dynamic model, and at least 50.17% lower than previous studies based on fixed bladder content volume. Conclusions Long-time measurement of multi-organ TACs with high temporal resolution enabled by a total-body PET/CT demonstrated that the clinical procedure with 20 min PET scan at 1 h after injection could be used for retrospective dosimetry analysis in most organs. As the bladder content contributed the most to the effective dose, a long-time dynamic model was recommended for the bladder wall dose estimation.

A revised compartmental model for biokinetics and dosimetry of 2-[18F]FDG

“…on dosimetry of 2-[ 18 F]FDG. The TIAC for brain in [ 31 ] was notably higher compared to the ones reported here and by other authors [ 2 , 4 , 6 , 7 , 32 ]. Brain-absorbed dose does not notably influence the effective dose though, since brain has a tissue weighting factor of only 0.01 [ 18 ].…”

“…by Jones et al [ 30 ] is consistent with the data by Mejia et al [ 6 ] and well described by the model of this study. The cumulative bladder excretion reported in [ 31 ] lies between the MIRD and the revised models and amounts to 5.8–7.1%IA at 1 h p.i. (compared to ca.…”

“…Recently, Hu et al [ 31 ] investigated an impact of TACs measured with a total-body high-sensitive PET/CT scanner up to 8 h p.i. on dosimetry of 2-[ 18 F]FDG.…”

Will extended field-of-view PET/CT depopulate the graveyard of failed PET radiopharmaceuticals?

“…Moreover, 64 Cu and 89 Zr cause a much higher radiation burden to the patient, not only because of the long halflife, but also because only about 20% of their radioactive decay occurs via positron emission. With an extended FOV PET camera, images can be acquired at later time points, allowing longer clearance times and thus enabling the use of 68 Ga and 18 F as a labelling option for larger proteins, for which previously longer-lived isotopes had to be used [5,27,28]. Radiolabelling of peptides and proteins can be easily achieved by conjugation of the peptide or protein with a suitable chelator, followed by complexation with a short-lived radiometal (salt) like [ 68 Ga]gallium chloride, or aluminium [ 18 F]fluoride.…”

First clinical experience of 106 cm, long axial field-of-view (LAFOV) PET/CT: an elegant balance between standard axial (23 cm) and total-body (194 cm) systems

“…In November 2018, the first human images from the uEXPLORER scanner were presented at a totalbody PET workshop, which were acquired at the Department of Nuclear Medicine, Zhongshan Hospital, Fudan University (Shanghai, China) [4]. Within a short period of time, a series of studies were reported to investigate the potential and future clinical applications of this total-body scanner [4,[9][10][11][12][13][14][15][16][17][18][19][20]. In one recent study, it was concluded that a fast PET protocol with a 30-45 s acquisition time in the uEX-PLORER PET/CT can provide equivalent image quality as the conventional digital uMI 780 PET/CT (United Imaging Healthcare Co., Ltd.) with longer clinical acquisition settings.…”