PURPOSE:Intraoperative radiation therapy is reportedly effective for local control and pain relief in colorectal cancer. However, this treatment requires a large number of medical personnel, which hinders expanded use of this method. A mobile electron linear accelerator for intraoperative radiation therapy has been developed and is now commercially available. This report analyzes the applicability of this accelerator to colorectal cancer. The applicability of the mobile accelerator is analyzed based on its specifications by simulating the intraoperative radiation therapy delivered to these patients with a conventional intraoperative radiation therapy unit.METHODS:From 1987 to 1999, 49 colorectal cancer patients underwent 54 surgical resections and received intraoperative radiation therapy to 75 sites.RESULTS:The mean intraoperative radiation therapy dose for colorectal cancer with the conventional unit was 22 (range, 10‐30) Gy. The mean electron energy level was 10 (range, 3‐30) MEV. Applicator size ranged from 4 to 10 cm in diameter. The mobile accelerator can achieve a dose rate of 10 Gy/min and an applicator unit size range of 3 to 10 cm in diameter, facilitating intraoperative radiation therapy for colorectal cancer. The electron energy limitation (12 MEV at maximum) suggests that the indications for this machine are limited. In our experience, 30 percent of patients received intraoperative radiation therapy with electron energy levels exceeding 12 MEV. Of these cases, 81 percent had macroscopic residual tumor and 69 percent had pain.CONCLUSION:An intraoperative radiation therapy mobile accelerator can cover 72 percent of the irradiation sites covered using our conventional unit. This accelerator is useful for intraoperative radiation therapy with curative intent for patients with no or slight residual tumor. Patients with gross residual tumor and pain may not be suitable.