{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"a87631e1ad60e476c66e4de8efbbc272a33d487e24209e9443565ef1b3243535","created":"2026-10-03T07:18:06Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"144e416198312dc073293efcbbc40d00cf6a9d1732e01eaa9c60463b4ab8bc0b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"med.flash.sparing-mechanism","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"Healthy tissue survives better when the dose arrives in a flash rather than slowly. The task is to find the physical or chemical process responsible.","posed_since":"2014","precise":"Identify the mechanism by which mean dose rates above roughly $4000\\ \\mathrm{rad}/\\mathrm{s}$ ($1\\ \\mathrm{rad} = 100\\ \\mathrm{erg}/\\mathrm{g}$), delivered in under $200\\ \\mathrm{ms}$, raise normal-tissue tolerance at fixed total dose (typically $1000\\ \\text{to}\\ 3000\\ \\mathrm{rad}$ single fraction) without a matching rise in tumour tolerance. Candidate classes: transient radiolytic oxygen depletion, inter-track radical-radical recombination altering peroxidation yields, differential iron and labile metal pools, immune and vascular responses. An answer is a quantitative model reproducing the measured sparing as a function of dose, dose rate, pulse structure and tissue oxygen tension.","problem_ref":null,"references":"","settled_by":"A model whose parameters are fixed by independent chemical and physiological measurements and that predicts, without refitting, the sparing measured across electron, proton and photon FLASH experiments in several tissues.","status_note":"As of 2025 oxygen depletion alone is widely judged insufficient and no consensus mechanism exists.","title":"Physical mechanism of normal-tissue sparing at ultra-high dose rate","topic_ref":"e183d5a2701f7e11dac3a5238c81e6d9a173fcc98c4f033d2937f114642a72e0"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"4dfc6486987618d7df84ce8c8da2834ce6ebdb1f7aab7c957c3e221923b3ee9f","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"a5598cbab081e1e656b5163dd0dc53313a8f3bba79970631ce4fe8786a446c60","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"QAmGz_c0mwgAcZ4m31quvJ6i7iLWjlJXeJNSbinz6LqiS-LJQtPWk7UkcH5Ea-HRoFomnlOiEKwR_E27xaJzAw"},"schema":"pubphys.envelope/1"},"record_hash":"4dfc6486987618d7df84ce8c8da2834ce6ebdb1f7aab7c957c3e221923b3ee9f","leaf_index":1682}