Evaluating the role of stereotactic radiosurgery in craniopharyngioma management

Craniopharyngiomas account for 2–5% of all primary brain tumors and 5–10% of pediatric brain tumors. Despite their benign histology, their location near the hypothalamus, pituitary gland, and optic pathways complicates management. Gross total resection, while effective, carries high risks of visual, endocrine, and hypothalamic dysfunction. Adjuvant radiotherapy after subtotal resection offers comparable control with fewer complications, but conventional fractionated radiotherapy is associated with long-term risks such as cognitive decline, secondary malignancies, and vascular injury. SRS delivers highly conformal, high-dose radiation with rapid dose fall-off, making it especially suitable for CPs adjacent to critical structures. Platforms include Gamma Knife, CyberKnife, and linear accelerator (LINAC)-based systems, with fractionated SRT (FSRT) used for larger or less favorably located tumors.

SRS vs. conventional radiotherapy

While conventional radiotherapy (54–60 Gy over 5–6 weeks) remains a standard adjuvant treatment, it exposes surrounding tissues to significant radiation, increasing risks of stroke, secondary tumors, and neurocognitive deficits-particularly in pediatric patients. SRS, by contrast, minimizes radiation to healthy tissues. Meta-analyses show no significant difference in long-term progression-free survival or endocrine outcomes between SRS and conventional radiotherapy, but SRS is associated with a lower incidence of hypothalamic obesity and other long-term sequelae.

Treatment outcomes by modality

Gamma Knife radiosurgery

Gamma Knife is the most extensively studied SRS modality for CP. Tumor control rates range from 36% to 100%, with higher rates (79.6–91.4%) achieved when marginal doses ≥12 Gy are used. Key factors influencing outcomes include:

• Dose-response: Doses below 10 Gy are associated with inferior control. A threshold of ≥12 Gy to ≥85% of the tumor volume optimizes local control.

• Tumor volume: Smaller tumors (<5 cm³ or diameter <19 mm) show better response and longer progression-free survival.

• Tumor composition: Solid tumors respond better than cystic or mixed lesions, which may require adjunctive therapies such intracavitary brachytherapy.

Long-term follow-up data indicate that control rates remain stable over time, with repeat SRS or combined approaches effective for recurrences.

CyberKnife and LINAC-based SRS

CyberKnife offers frameless, fractionated treatment, making it suitable for tumors near the optic apparatus or those with significant cystic components. Preliminary studies report control rates of 69.8–93.75%, with the flexibility to adapt treatment to cyst dynamics. LINAC-based systems also support both single-fraction and fractionated regimens, particularly for larger or irregularly shaped tumors.

Safety and complications

SRS demonstrates a favorable safety profile:

• Visual complications: Occur in ~4% of cases, primarily when the optic apparatus receives >10 Gy or is already compromised.

• Endocrine dysfunction: New deficits occur in ~6% of patients, often in those with pre-existing pituitary insufficiency.

• Other risks: Radiation necrosis and cognitive effects are rare. Maximum point doses >35 Gy may increase delayed neurological risks.

Dose constraints are critical, especially for the optic chiasm (tolerance: 8–10 Gy per fraction) and hypothalamus. In pediatric patients, stricter limits help preserve long-term quality of life.

Future directions

Several areas warrant further investigation:

• Dose and fractionation optimization: Refined protocols are needed for cystic, large, or recurrent tumors.

• Molecular targeting: BRAF mutations in papillary CPs open avenues for neoadjuvant targeted therapy (e.g., BRAF/MEK inhibitors) to shrink tumors before SRS.

• Prospective multicenter trials: Standardized outcome measures and longer follow-up are essential to validate SRS efficacy and safety.

• Quality of life metrics: Future studies should incorporate neurocognitive, endocrine, and psychosocial outcomes to fully assess the benefits of SRS.

Conclusion

Stereotactic radiosurgery is a cornerstone in the multidisciplinary management of craniopharyngioma, particularly for residual or recurrent disease. It offers high rates of tumor control with a favorable toxicity profile compared to conventional radiotherapy. Ongoing technical refinements, combined with molecular insights and personalized treatment planning, promise to further improve outcomes and quality of life for patients with this challenging tumor.