[Influence of radioactive concentration and storage time on radiochemical purity of 18F-FDG].
OBJECTIVE
To study the influence of the 18F-FDG radioactive concentration and the usual greatest storage time of the radiopharmaceutical at the Radiopharmacy Unit (RU) over its radiochemical purity.


METHODS
Thirty 18F-FDG preparations coming from different batches were studied. The radiochemical purity was determined at the RU by means of TLC to saline-diluted (1:10) and undiluted samples of each preparation, in the early 30 minutes since its arrival and 5 hours later. The radiochemical purity of the original 18F-FDG was determined at the PET radiopharmaceutical producer Laboratory (PETL) by means of HPLC in the early hour since the 18F-FDG dispensing.


RESULTS
The increase of 18F-Fluoride found in the (5 h-30 min) period was significantly greater in the samples without diluting than in the diluted ones (p < 0.0001). We found a significant correlation between the percent of this increase of 18F-Fluoride (y) and the radioactive concentration of the 18F-FDG (x): y = 0.00061x + 0.1759 (R2 = 0.198; p < 0.0005). The percent of 18F-Fluoride determined at the RU was significantly higher than the percent of 18F-Fluoride determined at the PETL (p < 0.0001). A significant correlation between the differences of the percent of 18F-Fluoride determined by TLC and HPLC (y) and the radioactive concentration (x) was found: y = 0.0139x + 0.3146 (R2 = 0.196; p = 0.016). A significant correlation among the differences of percent 18F-Fluoride determined by TLC and HPLC ([%F] RU - [%F] PETL), the radioactive concentration (RC) and the time since the radiopharmaceutical dispensing (t) was found: [%F] RU - [%F] PETL = 0.01159*RC (mCi/mL) + 0.250*t (h) - 0.01903 (R2 = 0.226; p < 0.014).


CONCLUSIONS
The stability of the 18F-FDG preparations with time increases when diminishing its concentration. We recommended the dilution of these preparations with physiological saline solution.
Unidad de Radiofarmacia, Servicio de Medicina Nuclear, Hospital Universitari de Bellvitge-IDIBELL, Barcelona. ijimenez@csub.scs.es
I R
IR
Jiménez Romero
M
M
Roca Engronyat
F
F
Campos Añón
J
J
Cordero Ramajo
I
I
Liarte Trías
A
A
Benítez Segura
M
M
Bajén Lázaro
N
N
Ferrán Sureda
R
R
Puchal Añé
C
C
Gámez Cenzano
D000107:Acetylation; D002851:Chromatography, High Pressure Liquid; D004355:Drug Stability; D004356:Drug Storage; D005462:Fluorine Radioisotopes / Q000032:analysis; D019788:Fluorodeoxyglucose F18 / Q000737:chemistry*; D011851:Radioactivity; D013997:Time Factors
D005462:Fluorine Radioisotopes; D019788:Fluorodeoxyglucose F18