Myxofibrosarcoma is one of the most prevalent histological types of primary malignant soft tissue tumors of the extremity. Radiation therapy is frequently employed as a post-operative treatment. In this case report, we present a 78-year-old male with a large tumor on his forearm. He refused surgical treatment. Over a period of seven years, recurrence and bleeding were repeatedly observed. Kochi oxydol radiation therapy for unresectable carcinomas (KORTUC) is a treatment modality that uses a hydrogen peroxide solution that adheres to the tumor surface (KORUTC I), while the solution is also injected into the tumor (KORTUC II). We treated the tumor with KORTUC I and II. A good response was observed. This case report highlights the effectiveness of KORTUC I and II. Reports on KORTUC for sarcomas are limited, underscoring the necessity for future examination of cases not indicated for surgical intervention.