Radiation or drug delivery source with activity gradient to minimize edge effects

[0023]Embodiments of intravascular radiation or drug delivery sources described below have longitudinal radiation or drug concentration gradients to minimize or to prevent proliferation of cells at the ends of the radiation or drug delivery source, commonly known as edge effect or candy wrapper. Cell proliferation response is believed to be caused by a very short transition area of high radiation or drug dose, corresponding to the therapeutic radioactivity or drug concentration level necessary to treat a lesion, to low or zero radiation or drug dose at the ends of a radiation or drug delivery source. By gradually decreasing radiation dose or drug dose levels by gradually reducing the radioactivity or drug concentration near the delivery source ends, the edge effect may be minimized or prevented altogether.

[0024]In one embodiment, a radiation delivery source has an identifiable radioactive region. The radioactive region has at least two radioactivity levels. The radioactive region has r