Functional imaging of tumours with 99Tcm-sestamibi pinhole scintigraphy

This study presents the advantages of pinhole over parallel-hole scintigraphy in the assessment of 99Tcm-sestamibi-related tumour biology. Twenty-five patients with malignancies underwent 99Tcm-sestamibi scintigraphy (Cardiolite, Dupont) before radiotherapy, 10 of whom had repeat scintigrams after the delivery of 25 Gy and at the end of radiotherapy. A total of 45 scintigrams with parallel-hole and pinhole collimation were evaluated for tumour avidity and ability to provide images for differential biological analysis within the tumour (areas of different uptake) or beyond the main mass (multifocality, satellite tumoral foci). The pinhole collimator was located with precision over the tumour area using a radiotherapy simulator. In 19 of 45 (42%) parallel-hole scintigrams the tumours were non-avid, whereas in 13 of 45 (29%) the tumours could be identified but the image quality was very poor. In contrast, tumour avidity was assessed in all 25 cases (100%) using pinhole scintigraphy and all pinhole images were evaluable for assessment of 99Tcm-sestamibi biology. The tumour-to-normal tissue (T/N) count ratio for the tumoral centre ranged from 1.71 to 4.36 (median 3.07) vs 1.54 to 3.20 (median 2.18) at the periphery, as assessed by pinhole imaging. Of 10 cases followed up with repeated scintigrams during radiotherapy, 2 showed an increasing T/N ratio during radiotherapy, both of whom did not respond to treatment. In the other eight cases, the T/N ratio decreased progressively during radiation treatment and all eight cases showed a varying degree of response on computed tomography or magnetic resonance imaging carried out 2 months after radiotherapy. It is concluded that 99Tcm-sestamibi tumour avidity can be successfully assessed with pinhole scintigraphy. Pinhole scintigraphy provides tumour images suitable for the evaluation of biological features related to radiolabelled pharmaceuticals. The premature observation that tumours showing increased 99Tcm-sestamibi uptake during radiotherapy correlated with poor therapeutic outcome requires further investigation.