Alveolar soft part sarcoma (ASPS) has the highest incidence of brain metastasis amongst sarcomas. There is a paucity of literature published focusing on radiation therapy for this condition. This is a single centre retrospective review of the treatment of three patients with 12 ASPS brain metastasis using single dose stereotactic radiosurgery (SRS). Five lesions were treated with low (<25 Gy) and seven with high (≥25 Gy) dose. Four lesions had a volume of >1.5 cm3 and were defined as large, while seven had a volume of ≤0.5 cm3 and were defined as small. The local tumor control as well as the clinical complication rates were studied. There was a statistically significant relation between treatment dose and tumor control rate. All large tumors treated with low dose recurred and required surgical removal within two months following SRS, while the large lesion treated with high dose recurred after 11 months. Five of the six small tumors treated with high doses were controlled, while the sixth required retreatment and was stable thereafter. No patient suffered from undue symptomatic radiation effects. The success rate following SRS for small ASPS metastases treated with high doses seems to be sufficient to justify the treatment. The short time for large tumor to recur, significant increase in tumor size requiring surgical removal of the tumors, makes low dose SRS unattractive. Based on this limited patient population, it seems that high dose SRS should be used for all ASPS brain metastases except for large tumors deemed surgically accessible.

BACKGROUND: Malignant peripheral nerve sheath tumors (MPNSTs) are rare, aggressive soft tissue sarcomas. MPNST intracranial metastasis is exceedingly rare with only 22 documented cases in the literature and, to our knowledge, only 1 case with intraparenchymal brain metastasis. Most have been managed surgically; however, 2 documented cases were treated with Gamma Knife radiosurgery. Excluding this case report, there are no other documented cases of linear accelerator-based stereotactic radiosurgery (SRS) to treat MPNST brain metastasis.
METHODS: A 41-year-old man with MPNST of the lung initially underwent tumor resection. He developed multiple systemic metastases that were managed with directed radiation therapy. A parietal brain metastasis was treated with linear accelerator-based SRS. Following SRS therapy, the patient was treated with a tropomyosin receptor kinase inhibitor. Complete resolution of brain metastasis was seen on brain magnetic resonance imaging 5 months after treatment with SRS. At 11 months after SRS, there was no evidence of recurrence or progression of the intraparenchymal disease. The patient continued to have stable extracranial disease on his ninth cycle of systemic treatment.
CONCLUSIONS: This report provides important insights into efficacy of linear accelerator-based SRS to treat MPNST brain metastases.