Proton Therapy Fails to Outperform Photons in Liver Cancer Trial

October 1, 2026 liver cancer, proton therapy, radiation oncology

A recent multicenter clinical trial has yielded unexpected results regarding the treatment of locally advanced hepatocellular carcinoma, the most common form of liver cancer. According to findings presented at the American Society for Radiation Oncology annual meeting in Boston, proton beam therapy failed to improve overall survival compared to traditional photon radiation therapy. Investigators on the randomized NRG-GI003 trial noted that patients treated with photon radiation therapy experienced overall survival rates more than twice as high as those assigned to the proton therapy group.

The study evaluated 115 randomized participants with advanced liver cancer, comparing the efficacy and safety of the two radiation modalities. Researchers initially hypothesized that proton therapy would extend median overall survival from 14 months to 24 months by delivering favorable dose distributions and sparing healthy nontarget liver tissue. However, the trial was stopped early for futility after an interim analysis revealed that photon-treated patients lived a median of 54.9 months, compared to 26.6 months for patients receiving proton therapy.

Despite the difference in overall survival, the two treatments showed no statistically significant discrepancies in progression-free survival or local tumor progression rates. Progression-free survival reached a median of 16.9 months in the proton arm and 13.7 months in the photon arm. Furthermore, the trial confirmed that proton therapy retained its expected dosimetric advantages. Protons significantly reduced radiation exposure to uninvolved tissue, which translated to a numerically lower rate of severe treatment-related adverse events. Grade 3 or higher adverse events occurred in 11% of the proton group compared to 24% of the photon group, though this difference did not reach statistical significance.

A detailed subgroup analysis offered further insights into the contrasting outcomes. While most cohorts showed no convincing preference for either radiation type, tumor size emerged as a significant predictive factor. Photon therapy dramatically outperformed proton therapy when treating larger tumors measuring 5 centimeters or greater, demonstrating a greater than twofold impact on overall survival. Conversely, the trial design utilized an isotoxic approach, meaning radiation doses were strictly limited by normal liver safety constraints. Only 58% of patients in the proton arm successfully received the highest planned dose level, leading experts to question whether tighter dose optimization could alter future outcomes.

Invited discussants at the meeting highlighted several potential explanations for the surprising data. Experts from Stanford Medicine suggested that the unexpectedly robust performance of the photon control arm was likely driven by rapid advancements in systemic therapies, particularly modern immune checkpoint inhibitor combinations. Additionally, researchers from the University of Washington noted that the study parameters prioritized liver preservation over maximum tumor dose escalation, suggesting that future investigations might reallocate the dosimetric benefits of protons to push clinical boundaries for high-risk patients.

Study investigators emphasize that modern liver radiation remains both safe and effective regardless of whether photons or protons are deployed, challenging historical perceptions of radiation as a last resort for advanced liver disease. However, determining the precise patient populations who benefit most from proton therapy requires additional evaluation.

Key Findings from the NRG-GI003 Trial

Photon therapy was associated with a median overall survival of 54.9 months, compared to 26.6 months for proton therapy.
Progression-free survival and local progression rates remained comparable between both treatment modalities.
Photon therapy demonstrated superior outcomes specifically in patients with larger tumors measuring 5 cm or greater.
Proton therapy successfully reduced exposure to healthy liver tissue, resulting in fewer severe adverse events.

Source: MedPage Today