A Study of the Drug I131-Omburtamab in People With Desmoplastic Small Round Cell Tumors and Other Solid Tumors in the Peritoneum

Single dose of IP RIT administered through an IP catheter with 131 I-omburtamab at 80mCi/m2

Group A participants will receive WAP-IMRT approximately 2-4 weeks after completing IP RIT. A dose of 30 Gy will be delivered in 20 fractions of 1.5 Gy given once daily, 5 days per week over the course of approximately 4 weeks