Photo Credit: Ekaterina Dorozhkina

Driven by technological advances, MRI-guided radiotherapy has become increasingly important in treating liver cancer.

Advances in technology have increased the importance of radiotherapy in treating liver cancer. As these advances, namely MRI-guided radiation therapy, become more common, experts outlined a literature summary and clinical guidance for these new techniques in Seminars In Radiation Oncology.

“When MR-linacs first became available, they quickly found use in organ sites that required excellent soft-tissue contrast and that moved due to breathing, such as in the abdomen,” Sabrina Prime, MD, and colleagues wrote. “This discernment was more important for stereotactic body radiation therapy (SBRT) treatments, which to this day continue to increase in importance for both primary and secondary liver tumors, particularly for those ineligible for surgical resection.”

MR-Guided Radiotherapy in Hepatocellular Carcinoma

In hepatocellular carcinoma, the researchers write, surgical options like liver transplant or partial hepatectomy are still the only curative measures available. Yet, they added, only 10% of patients who are newly diagnosed are ideal surgical candidates. Results from the recently published RTOG 1112 study showed that adding CBCT-guided SBRT to sorafenib improved median overall survival from 12.3 months to 15.8 months in surgery-ineligible patients with advanced hepatocellular carcinoma, Prime and colleagues wrote. This also came with improvements in progression-free survival without raising toxicity rates and further validated earlier studies in which SBRT showed “impressive local control” and strong survival in this indication.

Although patients with cholangiocarcinoma are good candidates for resection at similar rates to those with hepatocellular carcinoma, these patients have a dismal survival rate of about 5% to 10% over 5 years, the researchers noted. SBRT has yielded some success in this indication. A small retrospective study from researchers at UCLA found that MRI-guided adaptive radiation therapy produced a 1-year local control rate of 85.6% and a 1-year overall survival rate of 76% in patients with cholangiocarcinoma and tumors both inside and outside of the liver.

SBRT is well-studied in liver metastases, and a 2011 retrospective pooled analysis found that radiotherapy yielded a 1-year OS rate of 72%, with a 1-year local control rate of 67%. The researchers added that local control improved with increased dosage in that analysis, a finding that has been further backed up by more recent research. Prime and colleagues also mentioned that a phase 2 noninferiority study is underway to evaluate adaptive, breathing-gated SBRT MRI-guided radiotherapy against conventional ITV-based linac SBRT.

Implementation of Advancing Technology

Prime and colleagues also offered detailed guidance on workflow for the two main MR-guided radiotherapy systems, 0.35T and 1.5T. In addition to their detailed summaries, they made note of certain technical considerations for clinicians to consider in practice. In particular, Prime and colleagues pointed out that liver vascular stands out “quite nicely” in both the 0.35T and 1.5T systems and that “the luminal GI tract presentation can vary on MR imaging due to the varying presence of bowel gas, but in general the tract tends to be hyper-intense compared to liver parenchyma and is typically easily discernible from liver parenchyma when being utilized for online adaptive planning.” They also said that gadoxetate can safely and minimally invasively enhance the visualization of metastatic tumors.

“Through improved on-board imaging and innovations such as online adaptive re-planning and real-time MR-cine gating, MR-guided delivery of radiotherapy has improved the dosimetric therapeutic ratio of liver-directed radiotherapy, with early data demonstrating that this may translate to a clinical benefit for these patient populations,” Prime and colleagues concluded. “While there are significant workflow and technical considerations when implementing a MR-guided liver radiotherapy program that must be considered, it is clear that such a program can have significant benefits for patients with primary and secondary liver cancers.”