Clinical Outcomes of Carbon Ion Radiation Therapy for Malignant Peripheral Nerve Sheath Tumors

<h3>Purpose</h3> To investigate the outcome and toxicity of patients affected by malignant peripheral nerve sheath tumors (MPNSTs) treated with high-dose carbon ion radiation therapy (CIRT). <h3>Methods and Materials</h3> We retrospectively analyzed the outcome of 23 patients with MPNSTs treated between July 2013 and December 2020. Out of these, 13 patients (56.5%) had incompletely resected tumors, 8 patients (34.7%) experienced recurrence after surgery, and 2 patients (8.7%) had unresectable tumors. Before CIRT treatment, 4 patients underwent a second surgery after the first local recurrence (LR), and 1 patient underwent a third surgery for the second local relapse of the disease. Six (26%) patients received neoadjuvant chemotherapy. The most frequent tumor site was the brachial plexus (n = 9; 39.1%). In 5 patients (21.7%), neurofibromatosis type 1 disorder was found, while 4 patients (17, 4%) had radiation-induced MPNSTs. The median CIRT prescribed total dose was 69.8 Gy (relative biological effectiveness; range, 54-76.8) delivered in a median of 16 fractions (range, 15-22). Eleven patients (47.82%) were treated according to a sequential boost protocol with a median prescribed dose to clinical target volume LR of 45 Gy (relative biological effectiveness; range, 41.4-54). <h3>Results</h3> After a median follow-up time of 23 months (range, 3-100 months), the overall survival rates at 1 and 2 years were 82.38% and 61.51%, respectively. The 1-year and 2-year local relapse-free survival rates were 65.07% and 48.80%, respectively, and the 1-year and 2-year progression-free survival rates were 56.37% and 40.99%, respectively. No patients showed acute or late grade 4 toxicity or any treatment-related deaths. Ten patients (43.48%) reported acute toxicities of grade ≥ 2, which included dermatitis in 6 patients, mucositis in 2 patients, and peripheral neuropathy in 4 patients. Eight patients (34.78%) reported late toxicities of grade ≥ 2, mainly due to loco-regional neuropathy. <h3>Conclusions</h3> High-dose CIRT shows favorable local effects with acceptable toxicities in patients with gross residual and LR after surgery or unresectable malignant peripheral nerve sheath tumors. Advanced treatment modalities such as particle therapy should be considered for MPNSTs.