FUNCTIONAL IMAGING OF TUMORS WITH TC-99(M)-SESTAMIBI PINHOLE SCINTIGRAPHY

This study presents the advantages of pinhole over parallel-hole scint igraphy in the assessment of Tc-99(m)-sestamibi-related tumour biology . Twenty-five patients with malignancies underwent Tc-99(m)-sestamibi scintigraphy (Cardiolite, Dupont) before radiotherapy, 10 of whom had repeat scintigrams after the delivery of 25 Gy and at the end of radio therapy. A total of 45 scintigrams with parallel-hole and pinhole coll imation were evaluated for tumour avidity and ability to provide image s for differential biological analysis within the tumour (areas of dif ferent uptake) or beyond the main mass (multifocality, satellite tumor al foci). The pinhole collimator was located with precision over the t umour 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. I n contrast, tumour avidity was assessed in all 25 cases (100%) using p inhole scintigraphy and all pinhole images were evaluable for assessme nt of Tc-99(m)-sestamibi biology. The tumour-to-normal tissue (T/N) co unt 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 pinho le imaging. Of 10 cases followed up with repeated scintigrams during r adiotherapy, 2 showed an increasing T/N ratio during radiotherapy, bot h of whom did not respond to treatment. In the other eight cases, the T/N ratio decreased progressively during radiation treatment and all e ight cases showed a varying degree of response on computed tomography or magnetic resonance imaging carried out 2 months after radiotherapy. It is concluded that Tc-99(m)-sestamibi tumour avidity can be success fully assessed with pinhole scintigraphy. Pinhole scintigraphy provide s tumour images suitable for the evaluation of biological features rel ated to radiolabelled pharmaceuticals. The premature observation that tumours showing increased Tc-99(m)-sestamibi uptake during radiotherap y correlated with poor therapeutic outcome requires further investigat ion.