Effect of increased 99mTc/99Tc ratios on count rates in sentinel node procedures: a randomised study

The aim of this study was to evaluate the count rates of sentinel lymph nodes (SLNs) in patients with breast cancer in the operating theatre, using 99mTc-Nanocoll with different ratios of technetium-99m to technetium-99. After written informed consent had been obtained, we tested different ratios of 99mTc/99Tc-Nanocoll in a double-blinded randomised study performed in 161 patients. Twenty-five MBq/μg 99mTc-colloid albumin was prepared in vacuum. In 87 patients (group A) a 2-h elution was used and in 74 patients (group B) a 24-h elution was used. Patients were subcategorised into subgroups 1 and 3, in which an SLN procedure for breast carcinoma was performed simultaneously with lumpectomy, and subgroups 2 and 4, in which an SLN procedure was performed 2-3 weeks after prior excision biopsy. All patients were injected along the lateral border of the areola (two injections: 50 MBq/0.3 ml intradermally and 50 MBq/2 ml intraparenchymally). Ex vivo measurement of count rates was performed with a gamma probe. Comparing groups A and B in respect of registered counts per second (cps) of excised SLNs, a significant difference was found (P<0.004). When comparisons were made between subgroups 1 and 2 (2-h elution) and between subgroups 3 and 4 (24-h elution) in respect of registered cps of excised SLNs, no significant difference was found (subgroup 1 vs 2, P=0.825; subgroup 3 vs 4, P=0.915). Use of a 2-h elution in vacuum yielded a significantly higher count rate of maximum specific activity of 99mTc-colloid albumin in SLNs than was achieved using a 24-h elution in vacuum. SLN procedures performed 2-3 weeks after prior excision biopsy proved reliable as compared to SLN procedures performed simultaneously with lumpectomy. (orig.)