Gastrointestinal stromal tumors (GISTs) are generally considered resistant to radiation, but no prospective trials addressing efficacy and tolerability of radiation therapy have been carried out. Limited clinical experience suggests that selected GIST patients may benefit from palliative radiation therapy. The purpose of this prospective, non-randomized, multicenter study is to evaluate efficacy and safety of palliative radiation therapy in GIST patients who have progressive GIST during or after tyrosine kinase inhibitor therapy.