What is Stereotactic Body Radiation Therapy (SBRT) in relation to non-small cell lung cancer treatment?

Stereotactic Body Radiation Therapy (SBRT) in Lung Cancer Treatment

SBRT is a highly effective radiation therapy technique for early-stage non-small cell lung cancer (NSCLC) that delivers precise, high-dose radiation in fewer treatments than conventional radiotherapy, and is the preferred treatment for medically inoperable patients with stage I NSCLC. 1

Definition and Technical Aspects

SBRT (also called Stereotactic Ablative Radiotherapy or SABR) is characterized by:

• Delivery of very high radiation doses with extreme precision
• Treatment completed in 1-5 fractions (sessions)
• Use of 4-dimensional CT planning to account for respiratory motion
• Multiple radiation beams or arcs to minimize normal tissue exposure
• Biological equivalent dose (BED10) of at least 100 Gy for optimal outcomes 1

Clinical Indications for SBRT in Lung Cancer

Primary Indications:

• Medically inoperable patients with stage T1-2N0M0 NSCLC 1
• Operable patients who refuse surgery 1

Contraindications and Cautions:

• Patients with interstitial lung fibrosis (high risk of fatal toxicity) 1
• Tumors adjacent to major pulmonary vessels or hilar structures
• Patients with extremely limited life expectancy due to comorbidities 1

Efficacy Compared to Other Treatments

Compared to Standard External Beam Radiation:

• SBRT achieves superior local control rates of approximately 90% at 5 years 1
• SBRT should be preferred over standard EBRT for eligible patients (Grade B recommendation) 1

Compared to Surgery:

• Surgery (lobectomy) remains the standard of care for operable patients with early-stage NSCLC 1
• For medically inoperable patients, SBRT provides excellent local control and cancer-specific survival 1
• A pooled analysis of two randomized trials (STARS and ROSEL) showed comparable recurrence-free survival at 3 years between SBRT and surgery 1

Treatment Protocol Considerations

Dosing Recommendations:

• Biological equivalent dose (BED10) should be at least 100 Gy 1
• Evidence suggests doses higher than 150 Gy could be detrimental 1

Risk Adaptation:

• For central tumors, large-volume tumors, or patients with severe pulmonary comorbidity:
  • Dose reduction or increase in number of fractions is recommended
  • Risk-adapted schedule should be implemented (Grade B recommendation) 1

Safety and Toxicity Profile

• Acute treatment-related toxicity is uncommon 1
• Late toxicities may include rib fractures, dyspnea, and ventricular tachycardia 1
• Fatal toxicity risk is high in patients with pre-existing interstitial lung fibrosis 1
• Overall, SBRT has a favorable toxicity profile compared to surgery, especially in high-risk patients 2

Clinical Decision Making

For patients with early-stage NSCLC, the treatment algorithm should be:

1. Operable patients with stage T1-2N0M0 NSCLC:

   • Surgery (lobectomy) remains the standard treatment 1
   • SBRT should only be offered if patient refuses surgery 1

2. Medically inoperable patients with stage T1-2N0M0 NSCLC:

   • SBRT is the preferred treatment option 1
   • For peripheral stage I tumors, SBRT achieves local control rates of 90% at 5 years 1

3. Patients with borderline operability:

   • Multidisciplinary tumor board evaluation is essential 1
   • Recent evidence suggests comparable survival outcomes between SBRT and surgery in patients with impaired pulmonary function 2

Common Pitfalls to Avoid

• Failing to achieve adequate BED10 (should be at least 100 Gy)
• Not using risk-adapted protocols for central or large tumors
• Offering SBRT to patients with interstitial lung fibrosis without careful risk assessment
• Treating patients with extremely limited life expectancy due to comorbidities
• Not involving a multidisciplinary tumor board in complex cases

SBRT has revolutionized the treatment of early-stage NSCLC in medically inoperable patients, providing a highly effective, non-invasive alternative with excellent local control rates and acceptable toxicity.