What is the role of adjuvant radiation therapy (RT) in the treatment of retroperitoneal sarcoma?

Role of Adjuvant Radiation Therapy in Retroperitoneal Sarcoma

Adjuvant radiation therapy for retroperitoneal sarcoma is generally discouraged except for highly selected cases where local recurrence would cause undue morbidity, as it has not been validated in randomized trials and carries significant toxicity risks. 1

Current Recommendations Based on Guidelines

The 2022 NCCN Clinical Practice Guidelines in Oncology provide clear direction regarding radiation therapy (RT) for retroperitoneal sarcoma:

• Neoadjuvant RT is preferred over adjuvant RT when radiation is being considered 1
• Adjuvant RT is discouraged for retroperitoneal/intra-abdominal soft tissue sarcoma (STS) except in highly selected cases 1
• RT is not a substitute for definitive surgical resection with oncologically appropriate margins 1

When Adjuvant RT May Be Considered

Adjuvant RT may be considered only in the following scenarios:

• When reresection is not feasible 1
• To control microscopic residual disease 1
• In patients who have not received neoadjuvant RT 1
• When local recurrence would cause significant morbidity 1

Technical Considerations for Adjuvant RT

When adjuvant RT is deemed necessary, several technical aspects must be addressed:

• Dose recommendations:

  • 50 Gy external-beam RT for positive margins 1
  • Additional boost of 16-18 Gy for microscopically positive margins 1
  • 20-26 Gy boost for gross residual disease 1

• Tissue protection strategies:

  • A coordinated effort between surgeon and radiation oncologist is essential 1
  • Displacement of bowel from the tumor bed with omentum or other tissue displacers is recommended to reduce RT-related bowel toxicity 1

• Advanced RT techniques:

  • Intensity-modulated RT (IMRT), image-guided RT, and/or proton therapy can improve therapeutic effect 1
  • These techniques allow for better tumor target coverage while sparing adjacent normal tissues 1

Evidence on Efficacy

The evidence regarding adjuvant RT for retroperitoneal sarcoma shows mixed results:

• A 2008 study demonstrated that compared to surgery alone, adjuvant RT offered patients with retroperitoneal sarcoma improved local control and overall survival 2
• However, a 2016 study on retroperitoneal liposarcoma showed no statistical significance of adding adjuvant RT in local control (p=0.312), though there was a trend toward decreased local recurrence rate (38% vs 49%) 3

Margin Status Impact

Margin status is a critical factor in determining outcomes:

• A 2005 study found that margin status was predictive for both local control (p=0.0065) and survival (p=0.0012) 4
• 5-year survival was only 12% with positive margins versus 69% with negative margins 4

Neoadjuvant vs. Adjuvant RT

Current evidence favors neoadjuvant over adjuvant RT for several reasons:

• Neoadjuvant RT provides a defined tumor target 1
• It allows displacement of adjacent bowel 1
• It may reduce the risk of tumor seeding during surgery 1
• It may render tumors more amenable to resection 1
• A systematic review found neoadjuvant RT to be safe for retroperitoneal sarcoma 5

Potential Complications and Risks

Adjuvant RT carries significant risks that must be considered:

• Bowel toxicity is a major concern due to the tendency of normal bowel to occupy the void left by resection 1
• Significant complications including infection, hemorrhage, and bowel obstruction have been reported with postoperative RT 4
• The risk of complications appears higher with postoperative RT compared to preoperative RT 4

Practical Algorithm for Decision-Making

1. First decision point: Is the patient a candidate for neoadjuvant RT?

   • If yes, prefer neoadjuvant RT over adjuvant RT
   • If no (e.g., incidental finding during surgery), proceed to next step

2. Second decision point: Was complete resection with negative margins achieved?

   • If yes, adjuvant RT is generally not recommended
   • If no, consider adjuvant RT based on next criteria

3. Third decision point: Would local recurrence cause significant morbidity?

   • If yes, consider adjuvant RT
   • If no, close surveillance may be preferred

4. Fourth decision point: Can normal tissues be adequately protected?

   • If yes, proceed with adjuvant RT using tissue displacement techniques
   • If no, risks may outweigh benefits

Conclusion

While surgical resection remains the cornerstone of treatment for retroperitoneal sarcoma, the role of adjuvant RT is limited to highly selected cases. When considering adjuvant RT, clinicians must carefully weigh potential benefits against risks, particularly bowel toxicity. Advanced RT techniques and proper tissue displacement strategies are essential to minimize complications when adjuvant RT is deemed necessary.