Carbon Ion Radiotherapy for Unresectable Retroperitoneal Sarcomas

Abstract

Surgery is the mainstay of treatment for retroperitoneal soft tissue sarcomas (STS), and macroscopic total resection is possible in 50–70% of patients. The 5-year local control and overall survival rates obtained by surgery with/without adjuvant radiotherapy are reported to be approximately 50% and 50%, irrespectively. Due to the high linear energy transfer (LET) and the Bragg peak, carbon ion radiotherapy have been expected to be more effective and safe in the treatment for sarcomas than low LET radiation like photons. We evaluated the effectiveness and safety of carbon ion radiotherapy in patients with unresectable retroperitoneal STS. From 1996 to 2004, 17 (male/female:10/7) patients with retroperitoneal STS, not suited for resection, received carbon ion radiotherapy. Ages ranged from 16 to 64 (median 53 years). Eight patients had primary disease and nine recurrent disease. Histologic diagnoses were as follows: MFH (Malignant fibrous histiocytoma) in 5, liposarcoma in 3, MPNST (Malignant peripheral nerve sheath tumor) in 3, and other in 6 patients. Carbon ion radiotherapy was delivered in 16 fractions over 4 weeks. Four patients were entered onto a phase I/II dose escalation study of carbon ion radiotherapy and the remaining 13 patients a phase II study with fixed doses. Total doses: 52.8 GyE (3.3 GyE/Fr) in 1, 64.0 GyE (4.0 GyE/Fr) in 2, 70.4 GyE (4.4 GyE/Fr) in 12, and.73.6 GyE (4.6 GyE/Fr) in 2 patients. Clinical target volumes ranged between 57 and 1034 cm3 (median 416 cm3). Median survival time was 30 (range: 6–74) months for all patients and all living patients were followed more than 1 year. At 3 and 5 years, actuarial overall survival rates were 73% and 63%. Four patients experienced local recurrence, with time from carbon ion radiotherapy to local recurrence ranging between 3 to 35 months. At 3 years, actuarial local control rate was 63%. No severe acute and late reactions (grade 3–5 according to the RTOG criteria) were observed. Local control and overall survival at 3 yeas in patients with retroperitoneal STS treated by carbon ion radiotherapy are similar to those in reported data on patients treated by surgical resection with/without adjuvant radiotherapy. Despite the higher doses delivered to the tumors and the locally more advanced nature of the patients in this series, no severe toxicities were seen. Carbon ion radiotherapy is suggested to be an effective and safe treatment for retroperitoneal STS, but further experience and longer follow up are needed.