Stereotactic body radiation therapy for liver metastases

Although resection is the standard of care for liver metastasis, 80-90% of patients are not resectable at diagnosis. Advances in combination chemotherapy, particularly with targeted agents, have increased tumour response and survival in patients with unresectable metastatic colorectal cancer, but these techniques have limitations and may be associated with high recurrence rates. Some autopsy series have shown that as many as 40% of patients with metastatic colorectal cancer have disease confined to the liver; aggressive local therapy may improve overall survival in such patients. Local control of liver metastases can also ease hepatic capsular pain to improve quality of life. Stereotactic body radiation therapy (SBRT) offers an alternative, non-invasive approach to the treatment of liver metastasis through precisely targeted delivery of radiation to the tumours while minimising normal tissue toxicity. Early applications of SBRT to liver metastases have been promising with the reports of 2-year local control rates of 71-86% and other studies reporting 18-month local control rates of 71-93%. While these data establish the safety of SBRT for liver metastases, more rigorous phase II clinical studies are needed to fully evaluate long-term efficacy and toxicity results. In the interim, this review stresses that SBRT of liver must be performed cautiously given the challenges of organ motion and the low toxicity tolerance of the surrounding hepatic parenchyma.