Stereotactic Fractionated Radiotherapy (SFRT) in Osteosarcoma
SFRT should be considered as an alternative local treatment option for unresectable primary osteosarcomas, recurrent disease in patients unfit for surgery, and for small lung or bone metastases, though surgery remains the primary determinant of survival when feasible. 1
Primary Unresectable Osteosarcoma
For unresectable primary tumors, radiotherapy including advanced techniques (proton, carbon ion beam, or stereotactic approaches) should be considered, particularly when complete surgical resection is not feasible. 1
- Heavy particle RT and IMRT can be considered specifically for unresectable primary tumors 1
- For high-grade craniofacial osteosarcoma, RT can be proposed when complete surgery is not feasible or in patients with positive surgical margins 1
- The combination of surgery, radiotherapy, and chemotherapy can be curative in select cases, though the consistent use of full-dose chemotherapy is critical for radiotherapy response 2
Recurrent and Metastatic Disease
Stereotactic RT serves as a potential alternative local treatment option in patients unfit for surgery and for small lung or bone metastases, though surgical resection remains the primary treatment when feasible. 1
- For recurrent osteosarcoma with isolated lung metastases, treatment is primarily surgical, but stereotactic RT, radiofrequency ablation, or cryotherapy may be used as alternatives in patients unfit for surgery 1
- Radiofrequency ablation and stereotactic RT are potential alternative local treatment options for primary lung or bone metastases 1
- Surgery remains the primary determinant of survival in localized recurrent disease, and complete surgical resection with negative margins is mandatory for any chance of long-term survival 3
Clinical Outcomes and Evidence
Recent real-world data demonstrates favorable outcomes with stereotactic approaches:
- One-year local control rates of 81-82% have been achieved with SFRT in sarcomas, with symptom relief documented in 60% of treatment courses 4, 5
- SFRT for lung metastases is predictive of better local control (HR = 0.12, p = 0.007) and overall survival (HR = 0.55, p = 0.046) 6
- However, bone sarcomas demonstrate worse outcomes compared to soft tissue sarcomas, with bone sarcoma being predictive of worse local control (HR = 3.18, p = 0.043) and overall survival (HR = 2.05, p = 0.029) 6
Dosing and Technical Considerations
- The median total curative/definitive SBRT dose is 40 Gy in 5 fractions (range 30-60 Gy in 3-10 fractions) 7
- For SFRT techniques, 20 Gy in 1 fraction is most commonly used, typically followed by consolidative external beam radiotherapy to a median EQD2 dose of 32.5 Gy 4, 5
- Dose escalation moderately enhances local control, with SFRT dosimetric parameters (D10%, D90%, mean dose) being highly predictive of local control 6, 5
- Doses over 60 Gy showed no significant effect on local control in conventional fractionation 2
Critical Toxicity Considerations
Significant toxicity can occur, particularly in settings of concurrent chemotherapy and reirradiation, requiring careful patient selection and monitoring. 7
- Grade 3-4 acute and subacute toxicities occur in approximately 8% of cases 4
- Documented toxicities include myonecrosis, avascular necrosis with pathologic fracture, and sacral plexopathy 7
- Grade 3 toxicity has been observed particularly in patients receiving follow-up whole tumor radiation, with some attributable to unexpected rapid tumor regression 5
Prognostic Factors
Local control rates with RT plus surgery are significantly better than RT alone (48% vs. 22%, p=0.002), emphasizing the importance of combined modality treatment when feasible. 2
- Indication for RT and tumor location are prognostic factors for both survival and local control 2
- Patients with oligometastatic disease benefit most from stereotactic approaches 6
- Overall survival at 5 years for patients receiving RT for primary tumors is 55%, compared to 15% for local recurrence and 0% for metastases 2