ASTRO Releases Its First Clinical Guideline on Radiation Therapy for Gastric Cancer

The American Society for Radiation Oncology (ASTRO) has released its inaugural, evidence-based clinical guideline addressing the use of radiation therapy (RT) across the full spectrum of gastric cancer management. This document represents a defining moment for the field, offering a consolidated framework that integrates two decades of clinical trial data, evolving systemic therapies, and modern radiation technologies. The guideline, published in Practical Radiation Oncology, is the first of its kind to standardize RT recommendations for resectable, unresectable, locoregionally advanced, oligometastatic, and metastatic gastric cancer.

Gastric cancer remains a major global health challenge. It is currently the fifth most common cancer worldwide, and in the United States alone, more than 30,000 new cases are projected for 2025. Despite declining incidence over the last half-century, emerging epidemiologic evidence suggests a concerning rise among middle-aged adults, underscoring the need for continued refinement in both screening and therapeutic approaches. In the US, late-stage presentation remains common, necessitating careful coordination among surgical, medical, and radiation oncology specialists.

Why the Guideline Was Needed

Recent multicenter trials in both Western and Asian populations have reshaped the therapeutic landscape of localized gastric cancer. According to guideline chair ChristopherWillett, MD (Duke University) and vice chair Christopher Anker, MD (University of Vermont Cancer Center), “several major clinical trials have explored new treatment paradigms for potentially resectable and locally unresectable disease.” These trials concluded that treatment strategies centered primarily on perioperative systemic chemotherapy are frequently superior or noninferior to earlier approaches involving chemoradiation.

This shift created a critical need for an updated, evidence-based framework specifying where RT remains essential, where it remains optional, and where it should no longer be routinely used. The guideline is grounded in a systematic review of literature from 2001 to mid-2025, developed collaboratively with ASCO, ESTRO, and the Society of Surgical Oncology, and endorsed by ESTRO, SSO, the Royal Australian and New Zealand College of Radiologists, and the American Radium Society.

Key Recommendations

• Resectable Disease: Perioperative Chemotherapy as the Preferred Standard

For resectable gastric cancer, ASTRO confirms that perioperative chemotherapy, typically a fluorouracil, oxaliplatin, and docetaxel regimen administered before and after surgery remains standard-of-care.

Radiation is not routinely added when patients are eligible for and receive full perioperative chemotherapy.

• Role of Presurgical Chemoradiation in Select Patients

For patients unable to receive perioperative chemotherapy, the guideline recommends presurgical chemoradiation.

The goal is to improve the likelihood of achieving negative margins (R0 resection) and reduce early recurrence risk, especially in anatomically or biologically high-risk tumors.

Presurgical chemoradiation may also be considered for borderline resectable disease in patients already receiving perioperative chemotherapy, when the aim is to improve the chance of complete resection.

• Chemoradiation After Surgery

Postoperative chemoradiation remains an option for selected patients, particularly when high-risk features persist after surgery or when the quality of lymph node dissection is suboptimal.

• Immunotherapy in the First-Line Landscape

The guideline acknowledges the growing role of immune checkpoint inhibitors as first-line therapy in advanced or molecularly selected tumors. It integrates immunotherapy into multimodal planning where appropriate, marking radiation’s evolving interaction with systemic biologic agents.

• Definitive Chemoradiation for Non-Surgical Candidates

For patients with nonmetastatic disease who decline surgery or are not candidates for surgery, ASTRO recommends definitive chemoradiation.

This strategy can offer durable long-term control, both at initial diagnosis and at recurrence in radiation-naïve patients.

A detailed treatment algorithm accompanies the guideline to support decision-making for locally advanced disease.

• Palliative Radiation for Advanced or Metastatic Disease

For patients ineligible for curative therapy, palliative radiation is endorsed as an effective intervention for controlling bleeding, pain, obstruction, and other distressing symptoms.

Selected patients may be considered for re-irradiation when symptoms recur.

• Local Treatment of Oligometastatic Disease

For patients with limited metastases, the guideline conditionally supports using radiation or surgery for all visible metastatic sites in combination with systemic therapy. This reflects expanding evidence for aggressive local therapy in oligometastatic states.

Technical Specifications for Radiation Delivery

The guideline provides rigorous recommendations regarding target delineation, dose selection, and technology utilization:

Dose and Fractionation

• Standard dosing: 45–50.4 Gy, delivered in 1.8–2.0 Gy fractions

• Dose adaptation based on tumor burden and treatment intent

Target Volumes

• Gross disease (in unresected tumors)

• Postoperative tumor bed and anastomosis

• Regional lymph node stations according to tumor location

Advanced Technologies

The guideline prioritizes:

• Intensity-modulated radiation therapy (IMRT)

• Volumetric-modulated arc therapy (VMAT)

• Image-guided radiation therapy (IGRT)

• Respiratory motion management (4D-CT, breath-hold)

• Consideration of proton therapy where appropriate

These tools minimize radiation dose to the kidneys, liver, spinal cord, and heart, organs historically vulnerable in upper abdominal RT.

Shared Decision-Making as a Core Principle

A defining theme of the guideline is the prioritization of shared decision-making. Willett and Anker emphasize that treatment planning must involve comprehensive multidisciplinary discussion and active patient participation. Given the complexity and potential morbidity of therapy, transparent conversations about goals, risks, and expected outcomes are essential.

Conclusion

ASTRO’s first clinical guideline for the use of radiation therapy in gastric cancer represents a significant advancement in standardizing care for this heterogeneous and clinically challenging disease. By synthesizing two decades of research and aligning recommendations with contemporary systemic therapy and surgical standards, the guideline positions radiation therapy as a selective, precise, and context-dependent modality.

Its publication offers clinicians a rigorous, evidence-anchored roadmap that supports high-quality, individualized patient care across all disease stages.