{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"bc15d1c49b260d48c0cea74813635b41997955f4d7db265dd98e6502d5b77785","created":"2026-10-03T07:18:06Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["36b43a26a16b409cc0ec313f6a0af679c86f033453de7a4eda2e714c6e175783","5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"45db6bbf52f37fdb018611409ea6e8a7eea5df6765d265aed397f24824c50aba","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"med.ion-therapy.distal-edge","kind":"well-posed","literature_status":"partially-resolved","n":"1","parents":[{"note":"","parent_revision":"36b43a26a16b409cc0ec313f6a0af679c86f033453de7a4eda2e714c6e175783","relation":"special_case"}],"plain":"The last few millimetres of a proton beam are the most damaging per unit dose, which effectively pushes the treated region deeper than planned. By how much is not agreed.","posed_since":"2000","precise":"Quantify the shift in the biologically effective range at the distal edge of a spread-out Bragg peak, where $\\mathrm{LET}_d$ exceeds about $5\\,\\mathrm{keV}/\\mathrm{micron}$, for normal tissues of $\\alpha/\\beta$ near $200\\,\\mathrm{rad}$. Express it as a range extension in mm of water-equivalent thickness as a function of beam energy and modulation width. An answer is a number with uncertainty, per endpoint.","problem_ref":null,"references":"","settled_by":"Serial imaging or functional measurement of tissue change just beyond the planned range in patients, correlated with computed $\\mathrm{LET}_d$ and dose.","status_note":"Estimates of roughly 1 to 3 mm come from imaging studies, but the value remains endpoint dependent and unvalidated for most sites.","title":"Effective range extension at the distal falloff","topic_ref":"783c95cea555c72f61498fd08fa3ced7be4a4b07d67abcd2e5bc27204e6bdab5"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"248752810cfbf6979972c1093758c32c37b86fb6e9b1fde18d8d05bf55e21723","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"ec6e24379f5a9321e75023a5f626e0e97559179fec3c1e598495462718f76ccf","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"QjmT02q8sYrWwQ0KAEoVUIRGI0zNsDotwItgn5wwNh2-_CkvrVlPAcgNUysatmyLsEBf-S3gwLcf2AbUvyyIAQ"},"schema":"pubphys.envelope/1"},"record_hash":"248752810cfbf6979972c1093758c32c37b86fb6e9b1fde18d8d05bf55e21723","leaf_index":1693}