Clinical PET and PETCT by E. Edmund Kim Myung-Chul Lee Tomio Inoue & Wai-Hoi Wong

Author:E. Edmund Kim, Myung-Chul Lee, Tomio Inoue & Wai-Hoi Wong
Language: eng
Format: epub
Publisher: Springer New York, New York, NY

An early study has suggested that reduced FDG uptake after treatment appeared to coincide with a decline in the number of viable tumor cells [67]. A decline in 18F-FDG uptake during chemotherapy was significantly associated with a clinical response and survival [28, 68]. SUV may be helpful in the evaluation of the response to therapy. A significant reduction in SUV after therapy would be a good response. Tissue inflammation in response to radiotherapy may lead to false-positive results. Normal variants of 18F-FDG uptake in head and neck locations may also pose difficulty in interpreting images. So, there is no fixed quantitative scheme to use SUV to differentiate cancerous tissue from noncancerous tissue. Therefore, it is particularly important to have a baseline PET/CT scan to help differentiate incidental physiologic 18F-FDG-avid foci from malignant foci on subsequent posttreatment scans.

The timing of PET/CT after therapy is very crucial for accurate assessment of treatment response. The metabolic activity of residual viable tumor might be decreased immediately after the completion of radiation therapy, and it may take several weeks to recover their metabolic activity. Additionally, inflammation caused by radiation may result in diffuse increased FDG uptake, which can impair the identification of residual tumor. A report noted an improvement in both sensitivity and specificity of 18F-FDG PET when the scan was obtained at 8 weeks, as compared with 4–8 weeks, after the end of chemoradiotherapy. A false-positive or false-negative result on 18F-FDG PET/CT did not occur later than 8 weeks after radiation therapy [69]. A recent study has the consensus opinion that PET/CT should be ­performed about 10–12 weeks after the end of therapy [70].

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