High Dose-Rate Brachytherapy for the Treatment of Both Primary and Secondary Unresectable Liver Malignancies

Over the past three decades, the treatment of both primary and secondary liver malignancies has been improved by the development and optimization of multiple minimally invasive thermal ablative therapies. These advances have resulted in a myriad of benefits for patients including decreased morbidity, mortality, as well as increased longevity and quality of life. However, these therapies can only be performed within certain parameters. Thermal ablative techniques such as radiofrequency ablation (RFA) and microwave ablation (MVA) are recommended for small lesions under 3 cm due to decreased efficacy when attempting to treat larger lesions. Additionally, large vessels in close proximity to a target lesion may result in heat dissipation, termed the "heat sink" effect, and result in incomplete ablation of the lesion. Furthermore, thermal ablative techniques cause off-target damage when utilized near sensitive structures such as the diaphragm, stomach, or bowel, and if performed near thermosensitive bile ducts, can result in cholestasis . Noting these limitations, percutaneous high-dose-rate brachytherapy was brought into clinical practice by Ricke et al. in Europe in 2002 . This therapy utilizes an iridium-192 (192Ir) isotope to administer a cytotoxic dose of radiation to a target lesion. It is not susceptible to heat sink effects and can also deliver radiation with the precision necessary to cause tumor death without destroying the integrity of neighboring structures. Additionally, it can be used to treat larger tumors (\>3cm) as it is not associated the same size limitations as ablative techniques and can also be utilized to treat lesions that are not amenable to intra-arterial therapies (such as trans-arterial chemoembolization and yttrium-90 radioembolization). Since its inception, HDRBT has been evaluated through multiple studies investigating its use to treat lesions throughout the body including both primary and secondary liver malignancies such as hepatocellular carcinoma (HCC), cholangiocarcinoma, metastasis to the liver from colorectal cancer, pancreatic cancer , melanoma , and breast cancer . Its use in treating lymph node metastases has also been investigated . These studies have demonstrated the feasibility, safety, and clinical effectiveness of this method, establishing it as a therapeutic option when use of thermal ablation therapies is restricted. Most studies however, have been retrospective and have been performed outside the United States. Studying this therapy will add a crucial treatment option to our current armamentarium, filling a gap in currently available therapies and additionally allowing for further investigation of the use of HDRBT in a larger and more diverse population.