Potential Time Benefit in the Assessment of Recurrent Rat Rhabdomyosarcoma Using Positron Emission Tomography (PET) with 18Fluorodeoxyglucose Depends on Therapy-Specific Growth Delay

PURPOSE: To correlate the potential time benefit of (18)F-fluorodeoxyglucose positron emission tomography ((18)FDG-PET) in terms of early detection of recurrences of subcutaneously growing R1H tumors with therapy-specific parameters of recurrent tumor. MATERIAL AND METHODS: Twelve, eleven, and seven recurrences were followed after fractionated radiotherapy, surgery, and chemotherapy for 6 months, respectively, and (18)FDG-PET was performed weekly using a conventional full-ring whole-body PET scanner. By comparing PET results and actual tumor volume, the time benefit of (18)FDG-PET in detection of recurrent tumors of 0.1, 0.2, and 0.5 cm(3) was determined for the different treatment strategies. RESULTS: A significant time benefit of (18)FDG-PET of 26.9 days and 67 days was solely determined for recurrences after radiotherapy of 0.2 cm(3) and 0.5 cm(3), respectively. The potential time benefit showed a strong correlation with growth delay, which was increased after radiotherapy due to a pronounced tumor-bed effect. CONCLUSION: The potential time benefit of (18)FDG-PET is strongly determined by the growth kinetics of the recurrence. A tumor-bed effect, which is a phenomenon solely seen after radiotherapy, favors early detection by (18)FDG-PET. The experimental data, clinical experience and theoretical consideration all indicate a noticeable benefit of (18)FDG-PET especially after radiotherapeutic treatment.