Pet/Ct In Ct Simulation: Significance Of A Standardized Positioning Protocol For Head And Neck Radiation Therapy Planning

233; Table 1 Pre-RT 2 weeks 4 weeks 2 weeks post-RT Avg mucositis grade 0 1.33 2.67 1.67 FLT-PET SUVmax 10.5 3.25 1.55 2.15 FDG-PET SUVmax 8.53 5.53 4.27 5.13 Volume 94 Number 4 2016 Posters 923 mucositis in imaging interpretation, as FLT, unlike FDG, does not highlight metabolic or inflammatory activity of the tissue. A total of 9 PET scans were planned per patient (4 FLT-PET and 5 FDG-PET scans). Acute mucositis was recorded according to Common Terminology Criteria for Adverse Events version 4. PET scans were read by the same radiologist. Maximal standard uptake value of FDG-PET at each timepoint was compared with FLT-PET. Activity of both FLTand FDG-PET was also matched to the mucositis score to determine the correlation between PET activity and the severity of mucositis. Results: Three patients were enrolled in the first phase of the feasibility study. A total of 26 PET scans were obtained (missing was an FLT scan in 1 patient at week 2). All patients completed treatment according to the protocol. All patients developed mucositis, which nearly peaked at the end of week 4. Both FDG and FLT PET activity significantly decreased at week 2 and reached the lowest level at week 4. FDG-PET did not show activity in areas with the severe mucositis at and around the primary site, same as FLT-PET (see table). Interestingly, FLTas well as FDG-PET activity slightly increased at week 2 after RT at the mucosal sites while mocositis subsided to less than grade 2. At minimal follow-up of 1 year, all patients were without treatment failure. Conclusion: This study demonstrates that radiation-induced mucositis in oral cavity or oropharynx does not increase FDG or FLT uptake during radiation therapy. Author Disclosure: S. Song: None. J. Zweit: None. M.J. Fratkin: None. J.F. Williamson: None. D. Holdford: None.