Stereotactic Body Radiation Therapy for Gastrointestinal Cancers

The advent of stereotactic body radiation therapy (SBRT) has defined new roles for radiation therapy in the treatment of liver and pancreatic cancer. By minimizing the dose to the surrounding tissues and maximizing the dose to the tumor target, SBRT has the potential to considerably improve the therapeutic ratio in the treatment of these malignancies compared to conventional radiation therapy (RT). Given that many patients die of intrahepatic progression and subsequent liver failure, balancing optimal local control with risk of liver injury becomes a critical issue when treating patients with liver cancer, the most common one being hepatocellular carcinoma (HCC), with any intervention. SBRT has emerged as a treatment modality with excellent local control outcomes and acceptable side effects, similar or less than those of other local therapies such as radiofrequency ablation or transarterial chemoembolization, in appropriately selected patients. The implementation of SBRT requires a large multidisciplinary team (including radiation physicists and radiation therapists, in addition to surgical, medical, and interventional oncologists, as well as hepatologists) who can address challenges on many fronts including liver motion, incorporating multiple imaging modalities such as multi-phasic computed tomography (CT) and magnetic resonance imaging (MRI) for treatment planning, and image guidance at the time of SBRT. As only a small percentage of patients with liver metastases can undergo surgical resection, SBRT has now arisen as a treatment modality that achieves promising results regarding local control, and sustained local control has been associated with an increase in overall survival (OS) in patients with limited metastatic disease. Although these results are promising, up to this date there are no phase III clinical trials published on its use in a liver confined metastases cohort. Although most patients with pancreas cancer ultimately develop metastases, uncontrolled local disease is a large source of morbidity for up to a third of patients with locally advanced pancreatic cancer who die with locally destructive disease. Thus, there is motivation for developing efficacious and low morbidity radiation therapy treatments that may increase the chance for sustained local control in unresectable disease. SBRT brings unique challenges in this clinical scenario, given its proximity to the duodenum and other organs at risk, along with its considerable motion due to breathing and surrounding organ expansion. Freedom from local progression following SBRT has been reported as high as 78% at 1 year, and dose escalation has consistently been associated with an increased local control, but needs to be balanced against the potential increased risk for duodenal toxicity and bleeding.