Early monitoring of external radiation therapy by [18F]-fluoromethylcholine positron emission tomography and 3-T proton magnetic resonance spectroscopy: an experimental study in a rodent rhabdomyosarcoma model.
OBJECTIVE
To assess early radiation therapy (RT)-induced variations in total choline (tCho) concentration measured by proton magnetic resonance spectroscopy (H-MRS) and in (18)F-labelled fluoromethylcholine (FCH) uptake measured by PET in a rodent tumour model.


METHODS
Nine rats bearing syngenic rhabdomyosarcoma grafts in both thighs were irradiated (13 Gy, one fraction). H-MRS data and FCH-PET were acquired in the same imaging session prior to and 3, 9 and 16 days after external RT. Total choline concentration was expressed in arbitrary units as the area under the curve of the 3.2-ppm peak on H-MR spectra. FCH uptake was expressed as maximum standardized uptake value (SUV(max)) and as the % of injected dose per gram (%ID/g) after precise tumour delineation on hybrid PET-MR images. Pre- and post-RT data were compared using the Student's paired t test, and results were expressed as mean+/-S.D.


RESULTS
Seventeen tumours were available for analysis. A mean drop in choline concentration of 45% was observed 3 days after irradiation (P<.001), whereas a concomitant mean increase in SUV(max) of 41% was observed (P=.006). Choline concentration reincreased on later time points.


CONCLUSIONS
Opposite trend between increased FCH uptake and decreased tCho peak was observed at 3 days. Later (9 and 16 days), uptake remained stable and tCho peak reincreased.
Rommel
Denis
D
Department of Radiology and Medical Imaging, Université Catholique de Louvain, Brussels, Belgium. denis.rommel@uclouvain.be
Abarca-Quinones
Jorge
J
Bol
Anne
A
Peeters
Frank
F
Lhommel
Renaud
R
Lonneux
Max
M
Labar
Daniel
D
Gregoire
Vincent
V
Duprez
Thierry
T
D000464:Alginates / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002794:Choline / Q000031:analogs & derivatives* / Q000378:metabolism; D004195:Disease Models, Animal; D020723:Glucuronic Acid / Q000378:metabolism; D006603:Hexuronic Acids / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D049268:Positron-Emission Tomography; D011522:Protons; D051381:Rats; D012208:Rhabdomyosarcoma / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D015996:Survival Rate; D013997:Time Factors; D016896:Treatment Outcome
D000464:Alginates; D006603:Hexuronic Acids; D011522:Protons; C516370:fluoromethylcholine; D020723:Glucuronic Acid; D002794:Choline