A review of the sentinel node imaging protocol at a tertiary hospital in the Western Cape

Abstract

Introduction: Breast cancer has an orderly and predictable spread via the lymphatics to the sentinel lymph node (SLN). However, it is not possible to predict which lymph node basins will be involved. Hence, the accurate identification of the SLN is important to evaluate the spread of the primary tumour to the specific lymph node basins. Sentinel node imaging (SNI) involves the administration of a radiopharmaceutical at or close to the primary tumour for the pre-operative imaging, followed by the use of an intraoperative gamma probe during surgery. The current protocol requires the patient to visit the nuclear medicine department twice on the day prior to surgery with a possible third visit 24 hours after injection just prior to surgery. The aim of this study is to identify at which imaging time the SLNs are best identified and to propose possible changes to SNI protocol to reduce the number of imaging times without compromising the number of SLNs identified. The findings will be used to suggest possible changes to the current protocol at the research site, with the view of reducing the number of visits the patient needs to make to the nuclear medicine department. Materials and methods: This retrospective study used the data from 308 patients who underwent SNI procedures for breast cancer between January 2012 and June 2016. Demographic data were retrieved from the original patient request forms reflecting the date of the study, age of the patient and the site of the lesion in the breast. Histology reports retrieved from the hospital database detailed whether there was metastatic spread to the SLNs identified. Data from the imaging archive and reports included the site of the SLN, the number of SLNs identified and the time of imaging at which a sentinel node was identified. Chi-square analysis was used to find differences in the categorical measurements of the study site data and that of the seminal study. A Student’s t-test was performed to estimate the variation among the different imaging times during the SNI procedure. Results: The study site’s imaging protocol identified the SLN in 276 out of a total of 308 patients. Eighty-eight patients had histologically tumour positive SLNs.The results indicated identification of the SLN in 90% of the cases on the delayed 2-4 hours images compared to 27% and 43% on the dynamic and early delayed images respectively. Discussion: The study site yielded data consistent with that reported in Group B of the seminal study with identification of the SLN in 90% of the cases compared to 94% reported in the seminal study. Conclusion: The study site’s SNI protocol demonstrates the identification of the SLN in 90% of all the patients. The analysis suggests that the SNI protocol can be amended by performing only delayed imaging at 2-4 hours and excluding the dynamic and early planar images, thus resulting in decreasing the number of times that the patient is required to visit the department prior to scheduled surgery.