Assessment time of treatment response by PET-CT after superselective intra-arterial chemoradiotherapy for oral cancer

Abstract Objective Superselective intra-arterial chemoradiotherapy (SSIACRT) is an effective treatment for advanced oral cancer. However, in cases in which treatment is ineffective and the tumor remains, salvage operation is necessary; therefore, assessment of the treatment response is extremely important. With the use of fluorodeoxyglucose–positron emission tomography (FDG-PET)–computed tomography (CT) in addition to CT and magnetic resonance imaging, the accuracy improves for the assessment of treatment response. The study aimed to clarify factors that affect the accuracy rate of FDG-PET and FDG-PET scan time, considering the possibility of a salvage operation if the tumor remains. Methods From April 2006 to March 2017, 69 patients (52 men and 17 women) who underwent SSIACRT and received PET were evaluated. Results The average FDG-PET scan time for evaluating the treatment effect was 74.1 days (range, 48–126 days) after SSIACRT, and the rate of correct diagnosis was 75.4 %. All misdiagnoses were false positives. Multivariate analysis revealed that the correct diagnosis rate depended on the severity of oral mucositis (p = 0.025; odds ratio, 1.037). In 10 cases with residual tumor and five of six cases in whom size could be measured, no regrowth was observed in 3 months. Receiver operating characteristic curve analysis indicated that the time to obtain the correct diagnosis rate was 72 days. Conclusions Considering the state of oral mucositis, receiving FDG-PET after SSIACRT is appropriate at approximately 3 months; however, when oral mucositis is sufficiently improved, FDG-PET should be performed earlier.