Non-invasive monitoring of photodynamic therapy with 99technetium HMPAO scintigraphy.

The effect of photodynamic therapy (PDT) on tumour perfusion in both anaplastic (R3327-AT) and well differentiated (R3327-H) Dunning prostatic tumours was studied using the radiopharmaceutical 99Technetium hexamethylpropyleneamine oxime (99mTc-HMPAO). Tumours in the left flanks of rats (Copenhage x Fischer, F1 hybrids) were treated with interstitial PDT when their volumes reached 2-3 cm3. Qualitative and quantitative data from pre- and post-PDT scintigraphy revealed a light-dose-dependent shut-down of tumour perfusion which was also time-dependent. Maximal shut-down, following a 1,600 J light-dose, occurred about 8 h post-PDT. Light exposure 2 h after the intravenous administration of the photosensitiser (Photofrin II) produced a greater vascular shut-down than did light exposure 24 h after the administration of the drug. Regional differences in perfusion within treated and non-treated tumours were measured by tomographic procedures. Light-dose-dependent volumes of perfusion shut-down were demonstrated in addition to the naturally occurring regional differences in tumour perfusion. This radiopharmaceutical may have future utility for monitoring the clinical treatment of solid tumours with PDT.