Proton Therapy Is Superior to Photon Therapy (Conventional Radiotherapy) in Esophageal Cancer

Esophageal cancer is complex and difficult to treat and is often diagnosed at an advanced stage. At diagnosis, about 30-40% of patients may have locally advanced disease (stage II or III), with spread beyond the esophagus and possibly to nearby lymph nodes, but not to other organs.

“Standard treatment” for locally advanced esophageal cancer is generally multimodal, combining several approaches:

• Neoadjuvant Chemotherapy and/or Radiotherapy: Chemotherapy and/or radiotherapy is given before surgery to shrink the tumor and facilitate the operation.
• Surgical Resection: Surgery removes all or most of the tumor. A common procedure is esophagectomy, removal of part or all of the esophagus.
• Adjuvant Treatment: Chemotherapy and/or radiotherapy may be given after surgery to eliminate remaining cancer cells or prevent recurrence.

Radiotherapy nevertheless carries a risk of adverse effects. Choosing between its two main types—proton and photon therapy—is therefore critical for treatment effectiveness and side effects.

Proton and Photon Therapy: Key Differences

• Photon Therapy: X-rays deliver radiation to cancer cells. This is the method most commonly associated with conventional radiotherapy.
• Proton Therapy: High-energy proton beams are used. Protons release their energy when they reach the target tissue, reducing the risk of harming healthy tissues.

For Which Cancers Does Proton Therapy Stand Out?

Proton therapy is preferred for cancers where radiation poses a high risk to healthy tissue, including brain tumors—particularly those at the skull base—spinal cord tumors, and head and neck cancers.

For some cancers, such as certain skin cancers and lymphomas, no significant difference between proton and photon therapy has been observed.

The meta-analysis discussed here shows proton therapy to be more effective and safer than photon therapy in esophageal cancer. This may open new prospects and expand treatment options.

The Study's Main Findings

Researchers reviewed 45 studies of proton and/or photon therapy for esophageal cancer.

• Overall, photon therapy was associated with worse overall survival than proton therapy (hazard ratio [HR], 1.31; 95% CI, 1.07-1.61; I^2= 11%).
  • A hazard ratio of 1.31 indicates a 31% higher risk of death with photon therapy than with proton therapy. 
  • I^2= 11% indicates between-study heterogeneity, or variation. A low I^2 value (0-25% is generally considered low) suggests that the studies are broadly consistent. Here, they do not differ greatly in finding worse outcomes with photon therapy.
• Progression-free survival (PFS) did not differ significantly between treatment groups (HR, 1.29; 95% CI, 0.87-1.92; I^2= 40%).

Subgroup Analyses

• Among patients receiving radical treatment, those given photon therapy had worse overall survival and PFS than those given proton therapy.

• Neoadjuvant (preoperative) treatment was associated with no significant difference in overall survival between photon and proton therapy groups.

Adverse Effects

Proton therapy significantly reduced the risk of certain adverse effects, including:

• Grade 2 or higher radiation pneumonitis (lung inflammation)
• Grade 2 or higher pericardial effusion (fluid between the lung linings)
• Grade 4 or higher lymphopenia (low white blood cell count)

Conclusion

The researchers concluded that proton therapy reduces adverse effects and improves disease outcomes, but noted that the findings require “further confirmation in randomized clinical trials.”

Meta-analyses and observational studies can reveal important findings and trends, but their results generally need confirmation in randomized clinical trials (RCTs). RCTs are considered the “gold standard” for evaluating effectiveness and safety because randomization (random patient selection) minimizes bias and improves the reliability of results.