Purpose: To evaluate magnetic resonance (MR) imaging results after administration of gadolinium texaphyrin, a tumor-selective radiation sensitizer that is detectable at MR imaging, and to determine an appropriate intravenous dose of gadolinium texaphyrin for repeated injections during radiation therapy, the dose-limiting toxicity of reiterated doses of gadolinium texaphyrin, the maximal tolerated dose, the biolocalization of gadolinium texaphyrin (as assessed at MR examinations), and the response to treatment.
Materials and methods: Ten daily intravenous injections of gadolinium texaphyrin, each followed by whole-brain radiation therapy (total of 10 fractions, 30 Gy), were administered to patients with brain metastases in a multicenter study. At the study institution, 11 patients underwent MR imaging before and after the first injection, after the 10th injection, and 8 weeks after entry into the study.
Results: MR imaging revealed selective drug uptake in metastases, without enhancement of normal brain tissue. In 10 patients, tumor uptake was higher after the 10th injection than after the first injection, which indicated accumulation of gadolinium texaphyrin in metastases. One lesion was visible only after the 10th injection and not at the pretherapeutic MR examination with injection of conventional gadolinium-based contrast material. Response to treatment was defined as a reduction in the size of the metastases between the preinjection MR study and the last MR study; seven patients achieved partial remission with tumor regression exceeding 50% of the initial size, and four achieved a minor response with less than 50% tumor regression.
Conclusion: These preliminary results indicate that gadolinium texaphyrin is tumor selective and that brain metastases can be depicted at MR imaging long after the administration of gadolinium texaphyrin.