Purpose: Several drawbacks of endovascular brachytherapy for the treatment of coronary artery in-stent restenosis may be addressed by high-precision external beam radiotherapy (EBRT). The dosimetric characteristics of both treatment techniques were compared. Methods and Materials: The traversed volume of 10 coronary artery stents during the cardiac cycle was determined by electrocardiographically gated multislice spiral CT in 10 patients. By use of this traversed volume, high-precision EBRT treatment plans were generated for stents in the left circumflex (LCx), left anterior descending (LAD), and right coronary artery (RCA). The maximum dose to the nontargeted major coronary arteries was determined and compared to similar data calculated for endovascular brachytherapy. Results: High-precision EBRT targeted at LCx stents contributed a mean maximum dose ( D max ) of 83.5% (range: 71.6–95.3%) and 16.3% to the LAD and RCA, respectively. Targeted LAD stents contributed a mean D max of 39.3% (range: 14.5–94.8%) and 5.2% (range: 0–13.4%) to the LCx and RCA, respectively. Targeted RCA stents contributed a mean D max of 6.2% (range: 0–12.4%) and 5.8% (range: 0–11.5%) to the LCx and LAD, respectively. Endovascular brachytherapy targeted at LCx stents contributed a mean D max of 1.7% (range: 0.7–2.7%) and 1.0% (range: 0.6–1.4%) to the LAD and RCA, respectively. Targeted LAD stents contributed a mean D max of 5.2% (range: 0.5–11.4%) and 0.7% (range: 0.4–1.1%) to the LCx and RCA, respectively; targeted RCA stents contributed a mean D max of 0.3% (range: 0.2–0.5%) and 0.2% (range: 0.1–0.3%) to the LCx and LAD, respectively. Conclusions: Although the doses distributed throughout the heart were higher for high-precision EBRT compared to endovascular brachytherapy, they are expected to be clinically irrelevant when nontargeted major coronary arteries are not closely situated to the targeted vessel segment. These encouraging results warrant further investigation of high-precision EBRT as a potential alternative to endovascular brachytherapy for the treatment of coronary artery in-stent restenosis.
