612 Background: The purpose of this study was to retrospectively analyze the outcomes of patients with recurrent, metastatic, or unresectable rectal adenocarcinoma treated with mixed beam photon and high LET radiotherapy. Methods: Between 1995 and 2005, the high LET database was queried to identify patients with rectal adenocarcinoma. Local control and overall survival (OS) were calculated using the Kaplan-Meier method. Acute and chronic toxicities were graded using the common terminology criteria for adverse events (CTCAE) v4.0 grading system. Biological equivalent dose (BED) was calculated for tumor and normal tissue of both the photon dose and neutron dose for 10 patients. Results: 11 patients with recurrent, metastatic, or unresectable rectal adenocarcinoma were identified as being treated with mixed photon-neutron radiation. The median age of patients in the study was 58 (range: 38-79). There were 8 male patients and 3 female patients. Median follow-up was 6 months (range: 4-76 months). Patients received a median photon dose of 40Gy (range: 26-50.4Gy) and a median neutron dose of 8nGy (range: 6-10nGy). Seven patients received radiation given concurrently with 5-FU. The median OS was 16 months (range: 4-76 months), with 1 and 2-year OS of 56% and 22%, respectively. Local control was achieved in 9 of 11 (82%) patients. Local progression occurring in two patients occurred at 5 months after completion of RT. The median tumor BED in patients achieving local control was 72.5 Gy (range: 57.1-83.5 Gy). There was a nonsignificant difference in median normal tissue BED of patients with grade 3-4 late toxicity of 104.8 Gy (range: 81.1-115.1 Gy), compared with 95.3Gy (range: 89.0-104.6 Gy) for those patients with grade 1-2 late toxicity. Conclusions: Our experience demonstrates that treatment of unresectable rectal tumors with mixed photon-neutron achieved excellent local control. With the added capabilities of intensity modulated neutron radiation therapy (IMNRT), the incidence of treatment-related morbidity may be improved while taking advantage of the superior tumor control that high-LET radiation can impart. No significant financial relationships to disclose.
Long-Term Survival and Local Control Outcomes in Oligometastatic Colorectal Cancer Treated with Liver Stereotactic Body Radiation Therapy
