Choline uptake is increased in cancer tissues. In fact, the high metabolic rates of tumor cells require choline for the synthesis of phospholipids. 11C-choline and 18F-fluorocholine have been used in different types of tumor to study metabolic activity in vivo. Different chemical forms choline have been developed. We aimed to compare dosimetry of 18F-fluoroethilcholine (18F-FECH) to 18F-fluoromethilcholine (18F-FCH).
18F-FECH was synthetized in Reggio Emilia Hospital Lab. Three patients with biochemical recurrence of prostate cancer were injected with 18F-FECH. Dynamic PET/CT acquisition of the thorax and superior abdomen was performed starting immediately after injection. Whole-body PET/CT images were acquired 40 min and 100 min after 18F-FECH injection. Dosimetry to healthy organs (brain, heart, lung, liver, spleen, kidney, bladder, lungs) was calculated by OLINDA/EXM software, considering two integral computation methods: both acquisition points with biological removal (A) or only the delayed acquisition with no biological removal (B). The percentage differences (PD) between the time integrated-activity coefficients obtained with A and B methods for all CT contoured organs were calculated. We derived the Root Mean Square (RMS) errors and the standard deviations for the PD values in each patient. Organ dose values refer to A approach for time integrated-activity coefficients calculations.
18F-FECH dosimetry were compared to 18F-FCH results derived from literature.
The time integrated-activity coefficients obtained with method A are close to the same coefficients obtained using the method B: mean RMS error <6.5% and mean standard deviation <3.4%. The mean organ absorbed dose estimates to kidneys, spleen, liver and pancreas range in the interval (min, max) of (3.18-6.63), (2.18-2.6), (5.81-8.24), (3.64-6) mGy/MBq x10-2, respectively. Published data for 18F-FCH show a large variability, in fact reported values for kidneys, spleen, liver and pancreas range between 7.8-15, 3-6.3, 5.1-8.49, 1.6-6.29, mGy/MBq x10-2, respectively. Not all 18F-FECH values of the present study are included in this interval. However, even if our results don’t correspond completely to literature data, they are very close.
No significant difference were observed in dosimetric calculation using either A method or B method. Results for 18F-FECH dosimetry show a quite good agreement with already published data for 18F-FCH. Nevertheless further investigations would be needed to better understand if the differences observed are related to sample patients or dosimetry calculation steps such as contouring and imaging calibration.

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