Background: Liver cancer is the third most common cause of cancer related death worldwide, and hepatocellular carcinoma (HCC) accounts for 90% of all primary liver cancers, with pre-existing cirrhosis being a very strong risk factor for HCC development. Liver transplantation (LTx) is the best treatment for patients with HCC and advanced cirrhosis as both conditions can be very effectively treated at once. As LTx wait-lists can be many months, liver-directed therapies (LDT), including stereotactic body radiation therapy (SBRT) to one or few lesions are essential as oncologic temporizing measures to bridge patients to LTx and prevent progression outside of LTx criteria. However, due to the fear of further hepatic decompensation, many patients with advanced cirrhosis are excluded from receiving LDT. Rather, recent studies suggest that SBRT be of safe and practical use in this fragile patient population with advanced cirrhosis and HCC, and thereby reduce the rate of transplantation drop-out. This pilot prospective study will assess the feasibility, safety and efficacy of bridge-to-transplantation SBRT for patients with advanced cirrhosis and HCC. Methods: Patients with non-metastatic and unresectable HCC and Child-Pugh (CP)-B8 or worse cirrhosis who are within Milan criteria (one tumor ≤ 5 cm in diameter or no more than 3 tumors each ≤ 3 cm in diameter) and have been listed or recommended to be listed for liver transplantation will be eligible for participation. Eligible participants will undergo SBRT consisting of 40 Gy to be given in 5 fractions every other day to the only or largest lesion, provided that criteria for normal organ constraints are met. In cases where normal organ constraints are not met, the dose will be iteratively de-escalated to two dose levels (35 Gy in 5 fractions, then 30 Gy in 5 fractions). If normal organ constraints are unable to be met at 30 Gy in 5 fractions, the participant will be considered ineligible for SBRT and considered a screen failure. The primary endpoint is the proportion of participants who are transplanted or with localized disease control that meets Milan criteria within a year of SBRT. Secondary endpoints will include localized control rate (mRECIST), incidence of intra- or extra-hepatic progressive disease (mRECIST), overall survival, incidence of liver toxicity per CTCAE v5.0, incidence of non-classical radiation-induced liver disease (defined as CTCAE grade 4 AST/ALT elevation or an increase in CP score of ≥ 2 within 3 months of SBRT) and quality of life scores per QLQ-C30 and FACT-Hep questionnaires. The study is open, aiming to enroll 15 patients with 8 patients enrolled at time of submission. Clinical trial information: NCT03812289.