Radioguided surgery of parathyroid adenomas and recurrent thyroid cancer using the "low sestamibi dose" protocol

The aim of this study was to establish the clinical efficacy of the "low sestamibi dose" (LSD) protocol to perform thyroid and parathyroid radioguided surgery in a large series of patients homogeneously studied and operated on by the same surgeon. The LSD protocol was initially developed in our center to cure primary hyperparathyroid (PHPT) patients with a high likelihood of a solitary parathyroid adenoma (PA) by minimally invasive radioguided surgery (MIRS). Since then, the same protocol has been applied to differentiated thyroid cancer (DTC) patients with 131I-negative, but sestamibi-positive, locoregional recurrent disease in order to obtain radical radioguided extirpation of tumoral lesions at reoperation.

We reviewed the clinical charts of 453 consecutive patients referred at the surgical department at Padova University (Padova, Italy) to investigate a PHPT or a DTC recurrence: 336 patients (74.2%) met the inclusion criteria for radioguided surgery, and these patients were analyzed for the aim of this study. There were 298 patients affected by PHPT with a high likelihood of a solitary sestamibipositive PA and 38 DTC patients affected by 131I-negative, but sestamibi-positive, locoregional recurrence. All patients underwent a preoperative imaging work-up, including sestamibi scintigraphy (doubletracer subtraction scan in PHPT patients and single-tracer, wash-out scan in DTC patients) and high-resolution neck ultrasonography (US). The LSD protocol we developed consists of the intravenous injection of a very low (1 mCi) sestamibi dose in the operating theater just 10 minutes before commencing intervention for the purpose of radioguided surgery only. At variance with the traditional "high (20-25 mCi) sestamibi dose (HSD)" protocol in which imaging and radioguided surgery are obtained in the same day, in the LSD protocol, imaging and radioguided surgery are performed in different days. The LSD protocol allows some advantages over the HSD protocol: (1) more time for acquiring and interpreting preoperative imaging (planar scintigraphy, single-photon emission computed tomography [SPECT], US); (2) an accurate selection of patients to whom MIRS is offered, especially in countries where the prevalence of nodular goiter with sestamibi-avid thyroid nodules (exclusion criteria for MIRS) is relatively high, as in mid-south-European countries; (3) it facilitates the work planning in the operating theater (bilateral neck exploration requires an operating time of at least double to that of MIRS); and (4) the radiation exposure dose to operating theater personnel is very low-substantially negligible, using the LSD protocol: This aspect assumes great importance in countries where radioproteximetric rules are stringent, as in Europe.

PHPT patients. MIRS was successfully performed by a 1.5-2-cm skin incision in 287 of 298 PHPT patients (96.3%) in whom such an approach was scheduled on the basis of preoperative imaging, including 41 of 57 patients (71.9%) who had previously received thyroid or unsuccessful parathyroid surgery in another center. No case of major intraoperative complication was recorded. No case of persistent or recurrent PHPT was observed during postsurgical follow-up. DTC patients. A total of 79 metastatic lesions were intraoperatively detected by the gamma probe and successfully removed (68 of them had been correctly visualized at preoperative sestamibi scintigraphy). During subsequent follow-up, 18 patients (72%) were considered disease-free, whereas 7 had persistent disease (increased serum thyroglobulin levels). The radiation exposure dose to the surgeon using the LSD protocol was 1.2 uSi/hour, that is, 20-30-fold lower than that delivered with the HSD protocol used for PHPT patients and with the 131I protocol used for DTC patients with recurrence.

On the basis of our data, it can be concluded that the LSD protocol is a safe and effective protocol to perform in both MIRS in PHPT patients and radioguided reoperation in DTC patients with 131I-negative recurrence. Furthermore, from a radioproteximetric point of view, in comparison with other radioguided protocols used for the same purposes, the LSD protocol minimizes the radiation-exposure dose to the surgeon and operating theater personnel.