Simulation of spatial diffusion of platinum from carboplatin-impregnated calcium sulfate hemihydrate beads by use of an agarose gelatin tissue phantom.

OBJECTIVE To characterize spatial release of platinum from carboplatin-impregnated calcium sulfate hemihydrate (CI-CSH) beads by use of an agarose tissue phantom. SAMPLE 3-mm-diameter beads (n = 60) containing 4.6 mg of carboplatin (2.4 mg of platinum)/bead. PROCEDURES 18 L of 1% agarose was prepared and poured into 36 containers (10 × 10 × 10 cm), each of which was filled half full (0.5 L/container). After the agarose solidified, 1, 3, 6, or 10 CI-CSH beads were placed on the agar in defined patterns. An additional 36 blocks of agar (0.5 L/block) were placed atop the beads, positioning the beads in the center of 1 L of agar. The experiment was replicated 3 times for each bead pattern for 24, 48, and 72 hours. At these times, representative agarose blocks were sectioned in the x-, y-, and z-planes and labeled in accordance with their positions in shells radiating 1, 2, 3, 4, and 5 cm from the center of the blocks. Agarose from each shell was homogenized, and a sample was submitted for platinum analysis by use of inductively coupled plasma-mass spectroscopy. RESULTS Platinum diffused from CI-CSH beads at predicted anticancer cytotoxic concentrations for 2 to 5 cm. CONCLUSIONS AND CLINICAL RELEVANCE Results provided information regarding the spatial distribution of platinum expected to occur in vivo. Agarose may be used as a diffusion model, mimicking the characteristics of subcutaneous tissues. Measured platinum concentrations might be used to guide patterns for implantation of CI-CSH beads in animals with susceptible neoplasms.