A dosimetric comparison of conventional vs conformal external beam irradiation of a stented coronary artery utilizing a new fluoroscopic imaging detector system

Purpose. To determine whether conformal external photon beam irradiation may prevent or reduce the rate of restenosis of a stented coronary artery following percutaneous transluminal coronary angioplasty (PTCA). Optimal conformal external beam irradiation with limited cardiac dose requires adequate visualization of the stented vascular segment. With existing image intensifiers, identification of a coronary stent is poorly localized. We propose using an amorphous silicon panel detector to observe the movement of the stent during the cardiac cycle.

Long-term radiation-induced coronary complications can be minimized by: (a) reducing the radiation field sizes, (b) fractionating the total dose over several days, and (c) applying multiple treatment beams. Localization of the movement of the stent during the cardiac cycle may allow for the design of radiation fields that conform to the stented vessel segment. This scheme may permit gating the radiation beam on or off relative to movement of the stent within or outside the radiation fields, respectively.

Using a new solid-state amorphous silicon planar detector, with a dynamic range of 12 bits, fluoroscopic images of a Palmaz-Schatz coronary stent were obtained. The stent was centered in a polystyrene phantom 20 cm thick and imaged using a 90-kVp, 3.5-ma, source-detector and source stent distances of 114 and 100 cm, respectively. With the solid-state silicon detector, the stent was identified in a single video frame (1/30 s). This fast image acquisition should allow for mapping the motion of the stent during the cardiac cycle. The stent movement during the cardiac cycle may then be correlated with the QRS complex in the electrocardiogram.

The localization of a coronary stent during the cardiac cycle under fluoroscopy permits delivery of small conformal external radiation fields to treat stented coronary arteries, while minimizing radiation dose to surrounding normal cardiac tissue and vasculature. The best selection of treatment beam angles will be provided by high resolution fluoroscopic images of the stented region obtained from different beam directions. The three-dimensional movement of the stent, indexed in time with the QRS complex, will provide an important measure for gating radiation beams for conformal treatment delivery.