# Hepatocellular Carcinoma: SBRT and Liver-Directed Radiation
## Overview
Hepatocellular carcinoma (HCC) is the most common primary malignancy of the liver and typically develops in the setting of chronic liver disease, such as cirrhosis caused by hepatitis B or C infection, alcohol use, or nonalcoholic fatty liver disease/nonalcoholic steatohepatitis (NAFLD/NASH). Treatment decisions for HCC depend on tumor stage, liver function as assessed by the Child-Pugh classification, and the patient's performance status, commonly integrated within the Barcelona Clinic Liver Cancer (BCLC) staging system. Stereotactic body radiation therapy (SBRT) has emerged as an effective liver-directed treatment option for patients whose tumors are not suitable for transplant, surgical resection, or ablation. Historically, radiation therapy was considered unsafe for liver tumors due to the risk of radiation-induced liver disease (RILD). However, advances in SBRT techniques now allow delivery of ablative radiation doses with acceptable toxicity profiles. Current research is actively exploring how SBRT can be integrated with transplant eligibility criteria, transarterial chemoembolization (TACE), and systemic therapies such as immunotherapy.
## BCLC Staging and Treatment Algorithm
### Very Early/Early Stage (BCLC 0-A)
Patients classified as BCLC 0 have a single tumor measuring 2 cm or less, while BCLC A includes patients with either a single tumor or up to three tumors each measuring 3 cm or less. The standard treatments for these stages include surgical resection, liver transplantation following Milan criteria, or radiofrequency ablation (RFA). SBRT serves as an alternative to RFA particularly when tumors are not amenable to ablation due to factors such as central tumor location, proximity to major blood vessels, or prior failure of ablation.
### Intermediate Stage (BCLC B)
This stage is characterized by multinodular disease with preserved liver function. The standard of care is TACE. SBRT can be employed for tumors that do not respond to TACE, as a bridging therapy to transplantation, or in combination with TACE to enhance local control.
### Advanced Stage (BCLC C)
Advanced disease includes patients with portal vein invasion, extrahepatic spread, or an Eastern Cooperative Oncology Group (ECOG) performance status of 1 to 2. Systemic therapy, particularly with atezolizumab and bevacizumab as first-line treatment, is standard. SBRT has a role in achieving local control of portal vein tumor thrombus (PVTT) and managing oligometastatic disease.
## Clinical Evidence for Liver SBRT
### Phase II Trials
In a phase II trial by Bujold et al. (2013), 102 patients with locally advanced HCC were treated with SBRT doses ranging from 24 to 54 Gy delivered in six fractions. The study demonstrated a one-year local control rate of 87% and a median overall survival (OS) of 17 months. Radiation-induced liver disease was rare when patients were carefully selected.
### NRG-GI003 (Dawson et al., 2023)
The NRG-GI003 phase III trial compared SBRT to sorafenib in patients with HCC exhibiting macrovascular invasion or those unsuitable for standard locoregional therapies. The SBRT arm showed improved overall survival (15.8 months) compared to sorafenib (12.3 months). This trial provided the first randomized evidence directly comparing SBRT with systemic therapy for locally advanced HCC.
### Transplant Bridge
SBRT is frequently used as a bridging therapy to control tumor growth during the waitlist period for liver transplantation. Retrospective comparisons suggest that SBRT is comparable or superior to TACE in this role. Pathologic examination of explanted livers after SBRT often reveals high rates of tumor necrosis, indicating effective local tumor control.
### Versus RFA
Retrospective studies indicate that SBRT and RFA provide equivalent local control for tumors measuring 3 cm or less. SBRT may be preferred for tumors adjacent to major blood vessels where the heat sink effect limits RFA efficacy or for tumors located centrally within the liver. Randomized trials comparing SBRT and RFA are currently underway.
## Dose-Fractionation and Liver Function
### Dose Based on Child-Pugh Class
For patients with Child-Pugh A liver function, indicating good hepatic reserve, SBRT doses typically range from 40 to 50 Gy delivered in five fractions, corresponding to a biologically effective dose (BED10) of 72 to 100 Gy. Smaller tumors may be treated with 48 to 60 Gy over three to six fractions, and selected cases may receive single-fraction doses of 24 to 34 Gy. In patients with mild hepatic decompensation (Child-Pugh B7), dose reductions to 30 to 40 Gy in five fractions are recommended to minimize toxicity. For patients with more advanced liver dysfunction (Child-Pugh B8-9 or C), SBRT is generally not advised due to the high risk of hepatic decompensation. If SBRT is pursued in these cases, very conservative doses of 25 to 30 Gy in five fractions are used with close hepatology monitoring.
### BED Considerations
A BED10 of 100 Gy or greater is associated with the highest rates of local tumor control, exceeding 90%. For patients with good liver function and small tumors, achieving an ablative BED is the goal. In patients with compromised liver function, lower BEDs are accepted to maintain safety and reduce the risk of toxicity.
| Child-Pugh Class | Typical SBRT Dose | Fractions | BED10 | Notes |
|---|---|---|---|---|
| A (good function) | 40–50 Gy | 5 fx | 72–100 Gy | Ablative intent; goal BED10 ≥ 100 Gy |
| A (small tumors) | 48–60 Gy | 3–6 fx | 100–180 Gy | Highest local control |
| B7 (mild decompensation) | 30–40 Gy | 5 fx | 48–72 Gy | Dose reduction required |
| B8–9 / C | Generally not recommended | — | — | Very high risk of hepatic decompensation |
| Bridge to transplant | 30–50 Gy | 5 fx | Variable | Goal: tumor control during waitlist |
## Treatment Planning
### Simulation
Treatment planning begins with four-dimensional computed tomography (4D-CT) using intravenous contrast in the arterial phase to visualize the hypervascular HCC lesions. When tumors are better delineated on magnetic resonance imaging (MRI), MRI-CT fusion is employed. Fiducial markers, typically gold seeds, are placed percutaneously or endoscopically to facilitate tumor tracking during treatment. Abdominal compression is used to reduce respiratory motion, aiming for less than 5 mm residual movement. Breath-hold techniques, such as deep inspiration breath hold (DIBH) or expiratory breath hold, may be utilized for further motion control.
### Target Volumes
The gross tumor volume (GTV) is defined as the visible tumor on contrast-enhanced imaging, typically the arterial phase CT or MRI. The internal target volume (ITV) encompasses the GTV across all respiratory phases captured on 4D-CT. The planning target volume (PTV) is generated by adding a 3 to 5 mm margin to the ITV, supported by robust image-guided radiation therapy (IGRT). No clinical target volume (CTV) expansion is applied, similar to lung SBRT, as the high ablative dose compensates for microscopic disease. In cases of portal vein tumor thrombus (PVTT), the thrombus is contoured as a separate GTV.
### Organs at Risk Constraints (5-Fraction)
Dose constraints are critical to minimize toxicity. For the normal liver (defined as liver minus GTV), the mean dose should be kept below 15 to 18 Gy, ensuring that at least 700 cc of uninvolved liver receives less than 15 Gy, a concept known as the "critical volume" constraint. The stomach and duodenum should not receive maximum doses exceeding 30 to 35 Gy, with volumes receiving 25 Gy (V25) limited to less than 5 cc. The small bowel maximum dose should also remain below 30 to 35 Gy. For the kidneys, less than 35% of bilateral volume should receive 15 Gy or more. The spinal cord maximum dose should be under 25 Gy. Chest wall and ribs should have less than 30 cc receiving 30 Gy or more. For left lobe tumors, the heart maximum dose should be below 38 Gy, and the large bowel maximum dose should also remain under 38 Gy.
### Liver-Specific Planning Considerations
The "700 cc rule" is fundamental in liver SBRT planning, requiring that at least 700 cc of uninvolved liver receive less than 15 Gy in a five-fraction regimen to avoid RILD. For patients with Child-Pugh B liver function, this threshold is increased to 800 to 1000 cc to provide additional hepatic reserve. Beam arrangements often involve non-coplanar beams or volumetric modulated arc therapy (VMAT) arcs to maximize dose conformality and spare uninvolved liver tissue. The use of MR-linac technology allows real-time visualization of the tumor during treatment, enabling smaller margins and potentially higher doses while better preserving liver function.
## Radiation-Induced Liver Disease (RILD)
### Classic RILD
Classic RILD typically occurs between two weeks and four months after radiation therapy. It presents with anicteric hepatomegaly, ascites, and elevated alkaline phosphatase levels disproportionate to transaminase elevations. Pathologically, it corresponds to veno-occlusive disease (VOD). With modern SBRT and adherence to liver dose constraints, classic RILD is very rare. Risk factors include large irradiated liver volumes, pre-existing liver dysfunction, and concurrent use of hepatotoxic drugs.
### Non-Classic RILD
Non-classic RILD is more common in patients with underlying liver disease such as cirrhosis or hepatitis. It manifests as elevated transaminases exceeding five times the upper limit of normal or a decline in Child-Pugh score by two or more points within three months of radiation therapy. Clinically, it may present as hepatic decompensation with worsening ascites, jaundice, or encephalopathy. Monitoring liver function every one to two weeks during and after SBRT is essential, and co-management with hepatology specialists is recommended for cirrhotic patients.
A schematic of the BCLC staging system for HCC with standard treatment recommendations at each stage. SBRT is highlighted as an emerging option at multiple stages: alternative to RFA for very early/early stage, alternative to TACE or bridge to transplant for intermediate stage, and for portal vein tumor thrombus control in advanced stage. The figure shows where SBRT fits alongside the established treatment modalities at each BCLC level.
An axial contrast-enhanced CT image showing a 4 cm HCC in the right hepatic lobe (segment VII) with the SBRT dose distribution overlaid. The GTV (red) is well-defined on the arterial phase. The PTV (green) includes ITV + 5 mm margin. Isodose lines show the 100% prescription dose (40 Gy in 5 fractions, orange), 50% isodose (yellow), and 20% isodose (cyan). The uninvolved liver volume receiving <15 Gy is annotated as 850 cc (exceeding the 700 cc threshold). The stomach and duodenum are labeled with their respective max dose values.
A dose-fractionation nomogram for liver SBRT in HCC, with the x-axis showing tumor size (1-10 cm) and the y-axis showing recommended total dose in 5 fractions. Three curves represent Child-Pugh A (highest dose, 40-50 Gy), Child-Pugh B7 (intermediate, 30-40 Gy), and Child-Pugh B8 (lowest, 25-30 Gy). Annotations indicate the mean liver dose constraint and critical volume constraint for each Child-Pugh class. A warning zone marks Child-Pugh C as generally contraindicated for SBRT.
## Key Clinical Pearls
The Child-Pugh classification is the most critical factor in determining eligibility for SBRT and appropriate dosing. Patients with Child-Pugh A liver function can tolerate ablative doses ranging from 40 to 50 Gy in five fractions. Those with Child-Pugh B7 require dose reductions, while patients with Child-Pugh B8-9 or C are generally not candidates for SBRT due to the high risk of hepatic decompensation. The "700 cc rule," or an equivalent mean liver dose constraint, is the cornerstone of safe liver SBRT planning, as preserving adequate functional liver volume is essential to prevent RILD and hepatic failure. The NRG-GI003 trial provided the first phase III evidence demonstrating that SBRT improves overall survival compared to sorafenib in locally advanced HCC, supporting SBRT as a primary treatment option rather than solely a bridging therapy. For tumors adjacent to major blood vessels where RFA efficacy is limited by the heat sink effect, SBRT offers a non-invasive alternative with excellent local control. Non-classic RILD, manifesting as hepatic decompensation, remains the primary toxicity concern in cirrhotic patients; therefore, close hepatology co-management and serial liver function monitoring after SBRT are essential.
## References
- Bujold A et al. "Sequential phase I and II trials of stereotactic body radiotherapy for locally advanced hepatocellular carcinoma." *J Clin Oncol*. 2013;31(13):1631-1639.
- Dawson LA et al. "Stereotactic body radiotherapy (SBRT) vs sorafenib in patients with advanced hepatocellular carcinoma (HCC): results of the NRG-GI003 randomized phase III trial." *J Clin Oncol*. 2023;41(suppl 4):LBA490.
- Méndez Romero A et al. "Stereotactic body radiation therapy for primary and metastatic liver tumors: a single institution phase I-II study." *Acta Oncol*. 2006;45(7):831-837.
- Pan CC et al. "Radiation-associated liver injury." *Int J Radiat Oncol Biol Phys*. 2010;76(3 Suppl):S94-S100.
- Sapisochin G et al. "Stereotactic body radiotherapy vs. TACE or RFA as a bridge to transplant in patients with hepatocellular carcinoma. An intention-to-treat analysis." *J Hepatol*. 2017;67(1):92-99.