SBRT effective, well tolerated for unresectable liver metastases

A retrospective study in Hong Kong has shown that stereotactic body radiotherapy (SBRT) is an effective and well-tolerated treatment for patients with unresectable liver metastases.

“SBRT is recommended for patients who have unresectable liver metastases with ≤3 liver tumours, each with a diameter ≤6 cm, normal liver volume >700 cm³, Child-Pugh class A liver function, adequate organ function and Eastern Cooperative Oncology Group performance status [PS] of 0 or 1,” suggested the researchers. [Hong Kong Med J 2023;29:105-111]

“Patients with unresectable liver metastases often receive local ablative intervention after systemic therapy. SBRT is a noninvasive ablative technique that can be safely used for treating small hepatic lesions with high-dose radiation,” they wrote. [Int J Radiat Oncol Biol Phys 2010;76(3 Suppl):S94-S100]

To evaluate the use of SBRT in liver metastases, the researchers retrieved data from 31 patients (median age, 66 years; male, 61.3 percent; primary colorectal cancer, 71.0 percent) with liver metastases, including those with unresectable diseases and those who declined surgical resection. These patients received 1–2 weeks of SBRT (24–48 Gy in 3–6 fractions) at Tuen Mun Hospital between January 2012 and December 2017. Before and after SBRT, systemic treatment was given to 64.5 percent and 29.0 percent of patients, respectively.

During SBRT, the gross tumour volume (GTV) was determined using either intravenous contrast CT alone or contrast CT plus PET-CT. The clinical target volume (CTV), which accounted for the tumour position during respiration, was equal to the GTV. The planning tumour volume (PTV) was defined by adding an isotropic margin of 3–5 mm from the CTV or 7–10 mm in the cranial-caudal axis and 4–6 mm in the anterior-posterior and lateral axes.

The primary endpoint was local control, defined as absence of progressive disease within the PTV. The presence of new tumours outside the PTV was considered as intrahepatic outfield failure. Secondary endpoints were overall survival (OS) and toxicity.

In the study, the mean GTV and mean PTV were 26.9 cm³ and 91.8 cm³, respectively, with a mean biological equivalent dose to GTV of 79.8 Gy. The median follow-up was 18.9 months.

Local control rates were 93.5 percent at 1 year, 54.8 percent at 2 years, and 41.9 percent at 3 years, with a median time to progression of 10.9 months. The 1-year rate of outfield recurrence was 51 percent (n=16/31) in the total study cohort, while the colorectal cancer subgroup had a 1-year infield recurrence rate of 9.1 percent (n=2/22).

In the total study cohort, median OS was 32.9 months. Multivariable analysis showed that post-SBRT chemotherapy for disease progression was a prognostic factor for improved OS (adjusted hazard ratio, 0.327; 95 percent confidence interval, 0.108–0.991; p=0.039). Similar findings were shown in the colorectal cancer subgroup.

The patients tolerated SBRT well, without experiencing grade 2–4 adverse events (AEs). The most common grade 1 AEs were fatigue (19 percent), nausea (10 percent) and skin reaction (3 percent). Child-Pugh class was unchanged after SBRT.

“Our findings were comparable to previous research. [We found that] local control could be improved with increased radiation dose. However, OS improvement may depend on other factors, such as stage migration,” the researchers commented. “While associated with better OS, post-SBRT chemotherapy may only be given to patients with better PS.”

“SBRT can be considered in selected patients with unresectable liver metastases and those who refuse surgical resection for liver metastases,” they concluded.