Slow growing sarcomas are more sensitive to Proton and Neutron radiation but they are not yet able to treat deeply located lung tumors, it is mostly used for the superficially located sarcomas - unresectable primaries, tumors of face and skull etc. There are a few proton centers that do sarcomas and slow growing sarcomas are more sensitive to them, the one that is in Chicago area
http://www.neutrontherapy.niu.edu/neutrontherapy/ is a referral center for sarcomas but it is not good for the lungs applications as to do lungs (generally deep located small moving object close to vital structures) one needs to use some robotic unit like CyberKnife or Novalis, it is not possible yet to use with these radiation emitters - they are very large, only with the linear accelerators. I have seen that there are developments in the stereotactic neutron radiosurgery units but they are not there yet.
Radiation would have been my last choice after surgery and ablation. If the quote to treat that met is from Dr.Suh I second that 'F' said that he is one of the people in the field that knows this stuff, has been doing it for years now and is safe/reliable doctor to go with, although Dr.Littrup would be the better choice just because he does it a lot, every day and more then anyone everywhere and you should really go for the most experience in the technology based treatments, generally it takes 10 years and no less then 100 cases (300 is better) for the person to became an expert in the complicated field like that. But if there are any insurance/tactical considerations, I would go with Dr.Suh no problem. The thing is every ASPS patient would need to establish the good relationship with some good level ablation doctor (interventional therapy radiologist) to be able to evaluate any worrisome mets and deal with them in a time efficient manner. One month you can ablate them, the next month they can grow into something and the window of opportunity is closed.