In contrast, our preclinical SDRT studies indicate that O2 diffuses freely across the interstitial space within the encapsulated tumor volume (3); hence, the marked ASMase/ceramide-dependent acute hypoxia generated within the major portion of the tumor that receives full-dose SDRT equilibrates with the lesser pO2 reduction generated in the sculpted subdomain. Here, SMPD1 is linked to neoplasm.