Intraoperative nuclear guidance in benign hyperparathyroidism and parathyroid cancer

Evaluation of two intraoperative gamma detectors for assessment of 177Lu activity concentration in vivo

BACKGROUND

Patients with somatostatin receptor-expressing neuroendocrine tumours can be treated with intravenously administered ¹⁷⁷Lu-octreotate. Few patients are cured with the present protocol due to the current dose limitation of normal organs at risk, such as the kidneys. By locally administering ¹⁷⁷Lu-octreotate to the liver for the purpose of treating liver metastases, a substantially reduced absorbed dose to organs at risk could be achieved. The development of such a technique requires the capability of measuring the ¹⁷⁷Lu activity concentration in tissues in vivo. The aim of this study was to evaluate different performance parameters of two commercially available intraoperative gamma detectors in order to investigate whether intraoperative gamma detector measurements could be used to determine ¹⁷⁷Lu activity concentration in vivo.

RESULTS

Measurements were made using different sources containing ¹⁷⁷Lu. Response linearity, sensitivity, spatial resolution and its depth dependence, organ thickness dependence of the measured count rate and tumour detectability were assessed for two intraoperative gamma detectors. The two detectors (a scintillation and a semiconductor detector) showed differences in technical performance. For example, the sensitivity was higher for the scintillation detector, while the spatial resolution was better for the semiconductor detector. Regarding organ thickness dependence and tumour detectability, similar results were obtained for both detectors, and even relatively small simulated tumours of low tumour-to-background activity concentration ratios could be detected.

CONCLUSIONS

Acceptable results were obtained for both detectors, although the semiconductor detector proved more advantageous for our purpose. The measurements demonstrated factors that must be corrected for, such as organ thickness or dead-time effects. Altogether, intraoperative gamma detector measurements could be used to determine ¹⁷⁷Lu activity concentration in vivo.

Scintigraphic techniques in primary hyperparathyroidism: from pre-operative localisation to intra-operative imaging

INTRODUCTION

Primary hyperparathyroidism (PHPT) is an increasingly diagnosed disease worldwide. In most cases, PHPT is related to the presence of a solitary parathyroid adenoma (PA). Fifty percent or more of newly diagnosed PHPT patients are asymptomatic, and there is debate among endocrinologists and endocrine surgeons about whether or not such patients should be treated.

LOCALIZATION

Usually, in a PHPT patient with a solitary PA that is well localised pre-operatively, a parathyroidectomy with limited or minimally invasive neck exploration is offered. The diffusion of minimally invasive neck exploration procedures is a consequence of the significant improvement in the accuracy of pre-operative imaging (mainly scintigraphic) techniques; these techniques have changed the surgical strategy to PHPT, from the wide traditional bilateral neck exploration to limited neck exploration.

REVIEW

The present review considers developments during the past 10-15 years with regard to both the accuracy of pre-operative localising imaging techniques and intra-operative minimally invasive procedures in order to provide endocrinologists and endocrine surgeons with further information about the newly available diagnostic and therapeutic tools for use in PHPT patients with a solitary PA.

Technetium-99m sestamibi scintigraphy and helical CT together in patients with primary hyperparathyroidism: a prospective clinical study

44 consecutive patients with confirmed primary hyperparathyroidism (HPT) undergoing surgery were prospectively enrolled in the study. There were 13 (29.5%) men and 31 (70.5%) women with an overall median age of 59 years (range 23-78 years). Prior to successful parathyroidectomy both (99)Tc(m)-sestamibi/(99)Tc(m)-pertechnetate subtraction scintigraphy (SS) and helical CT were performed, and the results of imaging studies were compared against intraoperative findings. Final histopathology showed 40 (90.9%) solitary parathyroid (PT) adenomata (median size 18 mm, range 8-40 mm), that were in an ectopic location in 13 (32.5%) patients. Moreover, 3 (6.8%) patients had multiglandular disease (one patient with two PT adenomata, two patients with PT hyperplasia), while one (2.3%) patient had a PT carcinoma. The sensitivity and positive predictive value were 86.0% and 97.4% for SS, 88.1% and 94.9% for CT, and 100% and 97.4% for the combination of SS and CT, respectively. Calcium and parathyroid hormone (PTH) serum levels, and the mean size of the removed PT glands of patients with false negative results were lower than that of those with true positive results, but the difference was not significant. Among patients with solitary PT tumours (N=41) the sensitivity was 88.1% and 90.3% for SS and CT-scan, respectively. In conclusion, our study confirms the usefulness of SS, which should be the initial test for patients undergoing parathyroidectomy. However, the strategy of performing two tests in each patient with primary HPT could be of limited utility when the initial SS is positive.

Parathyroid cancer: biology and management

A review of all reports in the literature of parathyroid carcinoma (PTC) was undertaken to define an optimal management strategy for this rare condition. PTC is uncommon and its etiology of PTC is largely unknown although patients with familial hyperparathyroidism, multiple endocrine neoplasia type 1 and irradiation to the head and neck are at increased risk for developing the disease. PTC occurs with equal frequency in both sexes and is usually diagnosed in the fifth decade. En bloc resection of the carcinoma and the adjacent structures in the neck is the surgical treatment and is associated with an 8% local recurrence rate and a long term overall survival rate of 89% (mean follow up 69 months). In contrast simple parathyroidectomy results in a 51% local recurrence rate and 53% long-term survival rate (mean follow up 62 months). Adverse prognostic factors for survival were initial management with simple parathyroidectomy alone, the presence of nodal or distant metastatic disease at presentation and non-functioning PTC.