Development of a 9L rat brain tumor cell multicellular spheroid system and its response to 1,3-bis(2-chloroethyl)-1-nitrosourea and radiation - Deen,D.F.; Hoshino,T.; Williams,M.E.; Muraoka,I.; Knebel,K.D.; Barker,M. (J Natl Cancer Inst, 1980)