11C-methionine-PET for evaluation of carbon ion radiotherapy in patients with pelvic recurrence of rectal cancer.
OBJECTIVE
Progress of the novel carbon ion radiotherapy (CIRT) in the treatment of cancers has created the need for a method to accurately evaluate the response. We investigated whether L-[11C]methyl-methionine (11C-methionine) uptake at pre- and post-CIRT could be an early response predictor in patients with pelvic recurrence of rectal cancer.


METHODS
11C-Methionine-positron emission tomography (PET) was performed prospectively in 53 patients with pelvic recurrence of rectal cancer before CIRT, and 48 patients were performed 11C-methionine PET at 1 month after CIRT. 11C-Methionine tumor uptake was measured by the tumor to muscle ratio (T/M ratio). The T/M ratios were evaluated in relation to clinical outcomes such as local re-recurrence, distant metastasis, and survival. The response to CIRT was also judged by computed tomography (CT) and magnetic resonance imaging (MRI). 11C-Methionine PET judgment was compared with CT/MRI judgment regarding the relevance to clinical outcome.


RESULTS
Baseline T/M ratio was 5.27+/-1.90 (mean+/-SD) in patients without developing local re-recurrence and 7.66+/-3.17 in patients with local re-recurrence (p=0.023, Mann-Whitney U test). Post-CIRT T/M ratios were 3.10+/-1.28 in patients without local re-recurrence and 6.15+/-2.98 in patients with local re-recurrence (p=0.006, Mann-Whitney U test). By Kaplan-Meier analysis with log-rank test, patients with a baseline T/M ratio of <or=7.6 or a post-CIRT T/M ratio of <or=5.0 had significant lower pelvic re-recurrence rate. However, the percent change (reduction rate) from baseline to post-CIRT T/M ratio did not have significant relation to pelvic re-recurrence. There were no significant differences between 11C-methionine results (baseline T/M ratio, post-CIRT T/M ratio and percent change) and other clinical parameters (distant metastasis and survival).


CONCLUSIONS
11C-methionine-PET can be used for early prediction of local re-recurrence after CIRT. Because CIRT is local therapy, (11)C-methionine-PET cannot predict distant metastasis or survival after CIRT.
Koizumi
Mitsuru
M
Diagnostic Imaging, Molecular Imaging Center, National Institute of Radiological Sciences, Anagawa 4-9-1, Inageku, Chiba, Japan. mitsuru@nirs.go.jp
Saga
Tsuneo
T
Yoshikawa
Kyosan
K
Suzuki
Kazutoshi
K
Yamada
Shigeru
S
Hasebe
Mitsuhiko
M
Ohashi
Seiya
S
Abd-Elrazek
Sherif
S
Ishikawa
Hiroyuki
H
Sagou
Kenji
K
Tamura
Katsumi
K
Hara
Ryusuke
R
Kato
Hirotoshi
H
Yasuda
Shigeo
S
Yanagi
Takeshi
T
Tsujii
Hirohiko
H
D000230:Adenocarcinoma / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000556:secondary; D000328:Adult; D000368:Aged; D002250:Carbon Radioisotopes / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D008297:Male; D008715:Methionine; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000000981:diagnostic imaging*; D010386:Pelvic Neoplasms / Q000000981:diagnostic imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D011379:Prognosis; D011446:Prospective Studies; D019275:Radiopharmaceuticals; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*
D002250:Carbon Radioisotopes; D019275:Radiopharmaceuticals; D008715:Methionine