Annual Report

42. Functional Diagnosis and Evaluation of Therapeutic Effects of Cancer Using PET

Kyosan Yoshikawa, Katsumi Tamura, Yasunori Imai, Noriyo Matsuno, Masahisa Koga, Masakuni Kanai, Susumu Kandatsu, Hirohiko Tsujii, Tetsuya Suhara, Katsuya Yoshida, Kazutoshi Suzuki, Osamu Inoue, Fumio Shishido, and Hiroshi Fukuda

Keywords: PET, heavy ion beam therapy, detection of recurrent lesion

Positron emission tomography (PET) can demonstrate increased metabolic demand as visual images, and it provides alternative information for diagnosis which can be used to complement morphological observations. We studied usefulness of methionine-PET and FDG-PET to distinguish between radiation necrosis and recurrence of brain tumors after irradiation. Recurrent mass lesions of a brain tumor are usually revealed as an enhanced area in the MRI using Gd-DTPA. Some necrotic lesions caused after irradiation also show Gd-DTPA enhancement in MRI. It is often very difficult to distinguish between the two types. We studied 21 patients diagnosed with a brain tumor using C-11 methionine and FDG by PET. They had received carbon beam ion therapy and then showed some unusual findings in the brain MRI or CT study during the follow up period. They had received 16.8 GyE to 52.8 GyE beam doses. All patients were followed clinically for more than one year to five and half years until the clinical status of the patient, recurrence or radiation necrosis, was clearly known. There were six CR cases, nine recurrent cases and six radiation necrotic cases. It seemed that we could not distinguish recurrence from radiation necrosis by FDG-PET. But the population of cases was very small in the study; we need more time and cases to clarify this point. However, methionine-PET seemed able to distinguish between recurrence and radiation necrosis. When we classified our cases in two groups using a cut off value of 2.1 (TMR), sensitivity was 80 %, specificity was 70 % and accuracy was 73.3%. However, if we classified our cases in two other groups using a cut off value of 0.7 reduction ratio of methionine accumulation in the lesion which was a ratio calculated from the TMR value divided by pretreatment accumulation value, sensitivity, specificity and accuracy were 100%, 71 %, and 83.3 %, respectively. We concluded that the methionine-PET might be useful for distinguishing recurrent lesions after irradiation therapy from radiation necrotic lesions.

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