What field and dose would you prescribe for a an extra-renal rhabdoid tumor of the pelvis?

The more recent NWTS trials do not include these tumors, since rhabdoid are recognized to not be similar to Wilms, and the AREN0321 does not provide specific guidelines. Does anyone have experience with a significant number of these cases to provide insight into their management? Specifically, this is a 13 year-old who has an extra-renal rhabdoid tumor of the pelvis, resected with tumor spillage/rupture, no metastatic disease, no gross residual tumor and undergoing chemotherapy and autologous stem cell transplant as well.