Sentinel lymph node biopsy for papillary thyroid cancer: the effect of dose, tracer and application of massage

In patients with papillary thyroid cancer (PTC), sentinel lymph node (SLN) radio-guided biopsy is not routinely used for detection of involved neck lymph nodes (NLN); ^99mTc- antimony sulfide colloid (^99mTc- ASC) has been used for this purpose. In this study, besides ^99mTc-ASC another radiotracer, ^99mTc-phytate (^99mTc-P) with different doses and injection methods were evaluated.

Twenty-two patients, scheduled to undergo thyroidectomy for PTC, were injected for radio-guided SLN biopsy in the morning of operation in 3 groups: intra tumoral injection of about 1 mCi ^99mTc-P (group A; n=5); peritumoral injection of less than 3 mCi ^99mTc-ASC (group B; n=6); and peritumoral injection of 3 to 5 mCi ^99mTc-ASC with application of massage (group C; n=9). A patient refused to complete the study. A patient with follicular thyroid cancer was also excluded. No NLN was detected in the pre-operative ultra-sonographic examinations of all patients. Central neck dissection was done for all the participants. The presence of radio guided detected NLN and results of pathology were assessed.

In group A and B, no SLN was detected. NLNs were resected in 4 patients in group A and B; 2 of them involved by the tumor. In group C, 6 out of 9 patients (66.7%) had between 1 to 6 SLNs; the procedure failed to detect NLN in a patient in group C with surgically resected reactive NLN (failure rate 1 out of 7).

The results underscored the significance of SLN radio guided biopsy in patients with PTC; the radiotracer, dose and method of injection may affect the detection rate.