More accurate than MRI measurement of tumor size in breast cancer by using the peri-tumoral halo uptake layer method of the 18 F-FDG PET/CT scan.

OBJECTIVE: To evaluate the reliability of a method using the peri-tumoral halo layer (PHL) for assessing tumor size in breast cancer patients on the fluorine-18-fluorodeoxy glucose positron emission tomography/computed tomography (18 F-FDG PET/CT) scan compared to MRI and pathology.

SUBJECTS AND METHODS: Among 121 patients with breast cancer who underwent both 18 F-FDG PET/CT and MRI between March 2013 and June 2016, 59 patients were included in this study. Exclusion criteria were as follows: history of neoadjuvant therapy, history of pre-operative mammotome, insufficient pathologic/radiologic size report, clustered tumor, positive tumor resection margin, 18 F-FDG non-avid tumor. The PHL was examined by two nuclear medicine physicians. Tumor sizes (longest diameters) on 18 F-FDG PET/CT were estimated using margins defined as the inner line of the PHL. Pathologic tumor sizes were utilized as reference standards.

RESULTS: The PHL of each tumor was most commonly designated as the 20%-30% band of the maximum standardized uptake value (SUVmax) it exhibited an inverse correlation with tumor SUVmax. Tumor size on 18 F-FDG PET/CT showed a more linear correlation with pathology than that on MRI (r2 =0.91 vs 0.65). In Bland-Altman analysis, 18 F-FDG PET/CT showed significantly lower bias in size difference relative to pathology, compared with MRI (0.6±9.6cm vs. -1.9±17.3cm). Fluorine-18-FDG PET/CT showed more accurate T staging with pathology, especially in T3 cases, than MRI.

CONCLUSION: A method of tumor size determination, using PHL on 18 F-FDG PET/CT, showed more linear relationship and smaller size differences with pathology than MRI (average 0.6 vs. 1.9cm). It provides sufficient reliability and reproducibility for measuring tumor size in breast cancer.