Impact of minimum tumor dose of high dose rate intraluminal radiation therapy for esophageal carcinoma

High dose rate intraluminal radiation therapy (ILRT) for esophageal carcinoma was started at our hospital in 1982. The standard treatment was 10 to 12Gy of ILRT following 50 to 60Gy of external beam radiation therapy (EBRT). The dose of ILRT was prescribed at a level 5mm below the surface of mucosa. The thickness of residual tumor after EBRT, however, differed in each case. From August 1991 through April 1994, the residual tumor thickness after EBRT was measured in 17 patients by endoscopic ultrasonography. Minimum tumor dose was calculated by computer. Minimum tumor dose of ILRT correlated with the thickness of the tumor. The local control rate was significantly higher in patients treated with more than 9Gy of minimum tumor dose than in the less than 9Gy group. All of the more than 9Gy group were recognized as T1 or 2 (UICC,1987). Furthermore, analysis of the relationship between balloon diameter and minimum tumor dose disclosed that minimum tumor dose of more than 9Gy could be administered in patients where the maximum tumor thickness was less than 8 to 9mm. Consequently, ILRT is only effective for early stage esophageal carcinoma. Accordingly, endscopic ultrasonography has proved to be a very useful tool to identify patients with a high risk of local failure before ILRT.