Target definition by C11-methionine-PET for the radiotherapy of brain metastases.
OBJECTIVE
To evaluate the ability of 11C-methionine positron emission tomography (MET-PET) to delineate target volumes for brain metastases and to investigate to what extent tumor growth is presented by magnetic resonance imaging (MRI) and MET-PET.


METHODS
Three observers undertook target definition in 19 patients with 95 brain metastases by MRI and MET-PET images. MRI gross target volume (GTV) (GTV-MRI) was defined as the contrast-enhanced area on gadolinium-enhanced T1-weighted MRI. MET-PET GTV (GTV-PET) was defined as the area of an accumulation of MET-PET apparently higher than that of normal tissue on MET-PET images. The size of occupation ratio was determined using the following equation: SOR (%) of MET are within x mm margin outside GTV-MRI = the volume of the GTV-PET within x mm outside the GTV-MRI/the volume of the GTV-PET.


RESULTS
For GTV-MRI volumes of <or=0.5 mL, the sensitivity of tumor detection by MET-PET was 43%. For GTV-MRI volume of >0.5 mL, GTV-PET volumes were larger than GTV-MRI volumes and a significant correlation was found between these variables by linear regression. For all tumor sizes and tumor characteristics, a 2-mm margin outside the GTV-MRI significantly improved the coverage of the GTV-PET.


CONCLUSIONS
Although there were some limitations in our study associated with spatial resolution, blurring effect, and image registrations with PET images, MET-PET was supposed to have a potential as a promising tool for the precise delineation of target volumes in radiotherapy planning for brain metastases.
Matsuo
Masayuki
M
Department of Radiation Oncology, Chubu Medical Centre for Prolonged Traumatic Brain Dysfunction, Kizawa Memorial Hospital, Minokamo, Japan. matsuo@kizawa-memorial-hospital.jp
Miwa
Kazuhiro
K
Shinoda
Jun
J
Kako
Nobuo
N
Nishibori
Hironori
H
Sakurai
Kouta
K
Yano
Hirohito
H
Iwama
Toru
T
Kanematsu
Masayuki
M
D000368:Aged; D000369:Aged, 80 and over; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy / Q000556:secondary*; D001943:Breast Neoplasms / Q000473:pathology; D002250:Carbon Radioisotopes; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy / Q000556:secondary; D005260:Female; D005682:Gadolinium; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008715:Methionine; D008875:Middle Aged; D049268:Positron-Emission Tomography / Q000379:methods*; D012680:Sensitivity and Specificity; D047368:Tumor Burden
D002250:Carbon Radioisotopes; C086242:carbon-11 methionine; D008715:Methionine; D005682:Gadolinium