{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"f326c7771aa53b064d9404ad69b42a4d769bb29457ed5395a3cb05cfe10e2e4e","created":"2026-10-03T07:18:07Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"fe3007df885646ec848f3163aac36eed42681f522b192addf8c4fe8b5c737241","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"med.spatial-fractionation.dose-volume-effect","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"Tissue survives a huge dose when it is delivered in stripes tens of micrometres wide, but not when the same dose covers a broad area. What makes width matter is unclear.","posed_since":"1959","precise":"Explain the dose-volume effect in which normal tissue tolerates peak doses of several times $10^{4}\\,\\mathrm{rad}$ in beams of $25\\ \\text{to}\\ 100\\,\\mathrm{micron}$ width with spacing of $200\\ \\text{to}\\ 400\\,\\mathrm{micron}$, while tolerating only a few thousand rad in broad fields. Candidate mechanisms: preferential survival and migration of cells from unirradiated valleys, differential microvascular response, bystander signalling range, and immune recruitment. An answer is a mechanism predicting tolerance as a function of beam width, spacing and valley dose.","problem_ref":null,"references":"","settled_by":"Experiments varying beam width and spacing independently at fixed peak and valley dose, with direct observation of cell and vessel survival in valleys and peaks.","status_note":"Microbeam sparing has been reproduced repeatedly since the 1990s, with no consensus mechanism as of 2025.","title":"Why narrow beams spare tissue that wide beams destroy","topic_ref":"309568a913eeab83fa370b104ac678cba3936514b3451a97889575e821f58ffd"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"9710883231808fb035901e87eb783229c6e80a0cb54ce00f9d69cf59cd3f1b97","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"7cc3ccf91915be18393bcfe98707e849bf0c45a592a5179055d1a41f1ff1d86e","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"ZrsC76imhViUAoR6N-6f44ElBX3gNiVNXGOh2OZ0C2mFnZm7liDUF_B03I0QPGXSttlod_WNUp14Muh0R-y2Aw"},"schema":"pubphys.envelope/1"},"record_hash":"9710883231808fb035901e87eb783229c6e80a0cb54ce00f9d69cf59cd3f1b97","leaf_index":1726}