INTRODUCTION: Scintimammography using 99mTc sestamibi has proved to be useful in the differentiation of benign and malignant processes. However, the interpretation of images is subjective and depends on the experience of the observer. Quantification of radiopharmaceutical concentrations has been suggested as a method of identifying the nature of the tumor. Thus, a reference value needs to be established to create an index that can express malignancy.
AIM: To determine the best site to establish a region of interest for the reference value needed to calculate a 99mTc sestamibi concentration index for suspect breast lesions.
PATIENTS AND METHOD: Identical circular regions of interest were investigated on the scintigrams of both the breast with the suspect lesion and the contralateral breast of 97 patients. These regions expressed a background radiation for each breast. A comparison of the intensity of radiation, the counts/pixel ratio, of the regions of both breasts was performed for each patient. The mean difference and student t-test were applied for statistical analysis.
RESULTS: Five breasts with benign and 93 with malignant nodules (ductal = 83; lobular = 3; mucinous = 2; medullary = 2; high-risk intraductal lesion (carcinoma in situ)= 2 and papillary = 1) and their contralateral breast were studied. Background radiation of the breast with the suspect lesion was significantly greater than of the contralateral beast (t=4.543; p-value < 0.001). On average this value was 34% higher among ductal carcinomas and 23% higher among lobular tumors compared with breasts with benign and other types of lesions.
CONCLUSIONS: The region of interest used to identify a reference value should be established in the contralateral breast, as breasts with nodules produce an under-estimated index, particularly with more aggressive carcinomas, such as ductal and lobular tumors. This fact is probably due to the greater blood flow, the neoformation of vessels and anomalous vessels present in these types of tumors.
