Can different doses and fractionation schemes be used for each brain metastasis (metastatic lesion) in Stereotactic Radiosurgery (SRS) treatment?

From the Guidelines

Yes, you can give different doses and fractionation schedules to each brain metastasis during stereotactic radiosurgery (SRS). This approach, known as individualized dosing, allows for optimizing treatment based on the specific characteristics of each lesion. For example, a larger metastasis near critical structures might receive 24 Gy in 3 fractions (8 Gy per fraction), while a smaller lesion in a less eloquent area could receive 18-20 Gy in a single fraction. The dose selection should consider factors such as lesion size, location relative to critical structures (brainstem, optic apparatus, etc.), prior radiation history, and histology of the primary tumor.

Key Considerations

• Modern treatment planning systems and delivery platforms fully support this approach, allowing for simultaneous treatment of multiple lesions with different dose prescriptions in the same session 1.
• This individualized approach helps maximize tumor control while minimizing toxicity to surrounding normal brain tissue, potentially improving both efficacy and safety of the treatment.
• The biological effective dose can be maintained across different fractionation schemes by adjusting the total dose appropriately.

Evidence-Based Guidelines

• According to the EANO-ESMO clinical practice guidelines, SRS given in two to five fractions is preferred in patients with larger lesions or lesions in proximity of structures at risk 1.
• The NCCN guidelines recommend maximum marginal doses of 24,18, or 15 Gy according to tumor volume, based on the RTOG 9005 protocol 1.

Clinical Implications

• The use of individualized dosing in SRS for brain metastases has been supported by recent studies, including a prospective multicentre study that showed similar survival outcomes in patients with 2-4 versus 5-10 brain metastases 1.
• The approach allows for personalized treatment planning, taking into account the unique characteristics of each patient and their brain metastases.

From the Research

SRS Brain Mets: Dose and Fractionation

• The decision to give different doses and fractionation to each metastasis in SRS brain mets is complex and depends on various factors, including tumor size, location, and patient performance status 2, 3.
• Studies have shown that SRS can be safely used to treat multiple brain metastases, with a low risk of radiation-induced toxicity 3, 4.
• The use of single-fraction SRS or fractionated SRS (fSRS) can be considered, with the choice of dose and fractionation depending on the individual patient's needs 3, 5.
• For single-fraction SRS, tissue volumes receiving 12 Gy (V12) of 5 cm3, 10 cm3, or >15 cm3 were associated with risks of symptomatic radionecrosis of approximately 10%, 15%, and 20%, respectively 3.
• For fSRS, brain plus target volume V20 (3-fractions) or V24 (5-fractions) <20 cm3 was associated with <10% risk of any necrosis or edema, and <4% risk of radionecrosis requiring resection 3.

Considerations for Dose and Fractionation

• The dose and fractionation scheme should be individualized based on the patient's tumor characteristics, performance status, and other factors 5, 4.
• The use of SRS concurrent with systemic therapy (chemotherapy, targeted therapy, and/or immunotherapy) appears to be safe, with no increased risk of toxicity or radiation necrosis 6.
• The choice of dose and fractionation should also take into account the potential for radiation-induced toxicity, including radionecrosis and edema 3, 5.
• Further studies are needed to refine the dosimetric and toxicity reporting, and to develop predictive models of brain toxicity risks 3, 4.