Response evaluation of chemoradiotherapy in patients with pharyngeal cancer by PERCIST: Comparison to RECIST on F-18 FDG PET/CT study

Objectives The purpose of this study was to evaluate response to chemoradiotherapy (CRT) by PET Response Criteria in Solid Tumors (PERCIST) compared with Response Evaluation Criteria in Solid Tumors (RECIST).

Methods Study population consisted of 32 patients (age 65.2±11.3 years) with pharyngeal cancer. F18-FDG PET/CT was performed before and approximately 10 weeks after CRT. Response to therapy was compared between changes in peak standardized uptake value normalized for lean body mass (SULpeak) on PET by PERCIST and tumor size on CT by RECIST. SULpeak was calculated from 1.2cm diameter volume region of interest placed on the hottest lesion of tumor on PET. Tumor size was measured in the longest diameter on CT. Response evaluation was classified into 4 categories by PERCIST (CMR, complete metabolic response; PMR, partial metabolic response; SMD, stable metabolic disease; and PMD, progressive metabolic disease) and 4 categories by RECIST (CR, complete response; PR, partial response; SD, stable disease; and PD, progressive disease).

Results SULpeak was significantly decreased after CRT (before CRT, 12.2±5.4; after CRT, 3.4±1.4) (p<0.001). Most patients had good response to CRT both by PERCIST (CMR, n=15; PMR, n=9; SMD, n=1; and PMD, n=7) and RECIST (CR, n=7; PR, n=18; SD, n=3; and PD, n=4). Intermethod agreement was moderate between PERCIST and RECIST (kappa=0.43, 95% confidence interval: 0.19-0.67). In PR cases by RECIST (n=18), various results were observed by PERCIST (CMR, n=7; PMR, n=8; SMD, n=1; and PMD, n=2). In PMD cases with new lesions by PERCIST (n=7), 3 cases represented PR or SD by RECIST, which suggested PET/CT was more sensitive in detecting new lesions.

Conclusions This study demonstrated PERCIST allowed to assess metabolic response to CRT in patients with pharyngeal cancer. Evaluation by PERCIST was likely to offer more suitable treatment strategy than RECIST