Simultaneous Intraluminal Thermobrachytherapy: An in vitro Study

A multi‐institutional study on simultaneous intraluminal thermobrachytherapy (SITB) for advanced esophageal cancer was conducted in Japan. In this study, brachytherapy was administered by a small radioactive source stepping through a catheter in the esophagus, and hyperthermia was also applied by an endoesophageal coil. However, experimental or clinical findings on the spatial distribution of its antitumor effects around the esophagus are not available. Therefore, we developed an in vitro model of SITB using a high‐dose‐rate iridium‐192 stepping source and two human cancer cell lines (WiDr and A549), and determined the spatial distribution of the antitumor effects. According to this model, the antitumor effects steeply decreased as the source‐cell distance increased when cells of both cell lines were irradiated with 5 Gy without heat. When WiDr cells, a more resistant cell line to radiation and heat, were simultaneously irradiated and heated for 30 min at 44°C, the effects decreased much less steeply as the distance increased. For A549 cells, a more sensitive cell line, irradiation with hyperthermia even at 42°C made the decrease in the effects smaller. The largest antitumor effects can be expected at 5‐10 mm beneath the esophageal mucosa, where the endoesophageal coil can heat tissues most effectively. SITE can induce larger antitumor effects than brachytherapy alone, especially in submucosal disease, which would favor treatment of advanced cancer.