What is the risk of secondary malignancy and/or conversion to MPNST for patients with NF-1 who undergo radiation?  

Broadly speaking, this is certainly a possibility and this has been a reason why the community has triaged the application of radiotherapy to more high-risk cases (Williams et al., PMID 19117870). Just playing out the numbers independent of the application of radiotherapy, 100% of NF1 patients will ...