{"entity":{"id":"idea-bio2-let-rbe-ab-selects-protons","kind":"idea","name":"Use LET, RBE and alpha/beta to decide when protons beat IMRT","aka":[],"tldr":"Protons cost more than shaped X-ray beams. They are worth it when the extra punch where the beam stops, and the missing exit dose, widen the gap between killing the tumour and harming late-reacting tissue: an alpha/beta and RBE question, not a machine question.","summary":"Adult proton versus photon randomised trials have mixed toxicity results and scarce survival differences. Plans are still reported at a constant RBE of 1.1. The biological reason protons could win is site-specific: a low-alpha/beta tumour next to a low-alpha/beta late organ, plus high linear energy transfer at a distal edge that can be kept inside the target and off the organ. That predicted window should be written down before the trial reads out. The coverage-with-evidence idea asks payers to fund the trials; this idea asks the trials to test the radiobiology, not only the machine.","asOf":"2026-09-08","links":[{"label":"Paganetti, RBE values for proton beam therapy (IJROBP 2014)","url":"https://doi.org/10.1016/j.ijrobp.2014.07.001"},{"label":"PARTIQoL (NCT01617161)","url":"https://clinicaltrials.gov/study/NCT01617161"},{"label":"RADCOMP (NCT02603341)","url":"https://clinicaltrials.gov/study/NCT02603341"}],"tags":["radiation-wave5"],"related":["idea-fund-proton-coverage-with-evidence","proton-vs-imrt"],"cancers":["prostate","breast-hr-positive","esophageal","nsclc"],"sections":["radiation"],"technologies":["proton-therapy","imrt-igrt","carbon-ion","linear-quadratic-model","intensity-modulated-proton-therapy"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":["linear-energy-transfer","relative-biological-effectiveness","alpha-beta-ratio","bragg-peak","biologically-effective-dose"],"trials":["partiqol","radcomp"],"people":[],"bottlenecks":["b-surgery-radiation-innovation"],"keyPapers":["paper-paganetti-proton-rbe-ijrobp-2014"],"journals":[],"dependsOn":[],"notes":[],"hypothesis":"Pre-specifying tissue alpha/beta and a variable-RBE (LET-weighted) proton plan predicts which anatomies will show less late toxicity at equal tumour control in proton-versus-IMRT randomised trials. A constant 1.1 RBE plan will not.","rationale":"Constant RBE 1.1 is a reporting convention. Variable RBE rises at the distal edge and is larger for low-alpha/beta late tissues. If that physics does not show up in PARTIQoL, RADCOMP and the NRG oesophageal and lung comparisons, the adult proton case rests only on integral-dose and second-cancer arguments, not on a wider therapeutic window for the index tumour.","test":"On PARTIQoL (prostate), RADCOMP (breast), and the NRG/Lin oesophageal proton-versus-photon trials, lock an alpha/beta pair and an LET-weighted RBE model before unblinding the late-toxicity analysis, and ask whether the predicted window matches the result. A miss is as informative as a hit.","maturity":"preclinical-evidence","actor":"research","cost":"small","horizonYears":5},"route":"/ideas/idea-bio2-let-rbe-ab-selects-protons/","neighbours":{"idea":[{"id":"idea-fund-proton-coverage-with-evidence","kind":"idea","name":"Pooled coverage-with-evidence for proton therapy across all centres","route":"/ideas/idea-fund-proton-coverage-with-evidence/"}],"pairing":[{"id":"proton-vs-imrt","kind":"pairing","name":"Caution: proton therapy vs IMRT","route":"/pairings/proton-vs-imrt/"}],"cancer":[{"id":"breast-hr-positive","kind":"cancer","name":"HR-positive / HER2-negative breast cancer","route":"/cancers/breast-hr-positive/"},{"id":"nsclc","kind":"cancer","name":"Non-small-cell lung cancer","route":"/cancers/nsclc/"},{"id":"esophageal","kind":"cancer","name":"Oesophageal cancer","route":"/cancers/esophageal/"},{"id":"prostate","kind":"cancer","name":"Prostate cancer","route":"/cancers/prostate/"}],"section":[{"id":"radiation","kind":"section","name":"Radiation Therapy","route":"/fronts/radiation/"}],"technology":[{"id":"carbon-ion","kind":"technology","name":"Carbon-ion therapy","route":"/technologies/carbon-ion/"},{"id":"imrt-igrt","kind":"technology","name":"IMRT / IGRT (modern external beam)","route":"/technologies/imrt-igrt/"},{"id":"intensity-modulated-proton-therapy","kind":"technology","name":"Pencil-beam scanning and intensity-modulated proton therapy","route":"/technologies/intensity-modulated-proton-therapy/"},{"id":"proton-therapy","kind":"technology","name":"Proton therapy","route":"/technologies/proton-therapy/"},{"id":"linear-quadratic-model","kind":"technology","name":"The linear-quadratic model and fractionation","route":"/technologies/linear-quadratic-model/"}],"term":[{"id":"alpha-beta-ratio","kind":"term","name":"Alpha/beta ratio","route":"/terms/alpha-beta-ratio/"},{"id":"biologically-effective-dose","kind":"term","name":"Biologically effective dose (BED) and EQD2","route":"/terms/biologically-effective-dose/"},{"id":"bragg-peak","kind":"term","name":"Bragg peak","route":"/terms/bragg-peak/"},{"id":"linear-energy-transfer","kind":"term","name":"Linear energy transfer (LET)","route":"/terms/linear-energy-transfer/"},{"id":"relative-biological-effectiveness","kind":"term","name":"Relative biological effectiveness (RBE)","route":"/terms/relative-biological-effectiveness/"}],"trial":[{"id":"partiqol","kind":"trial","name":"PARTIQoL","route":"/trials/partiqol/"},{"id":"radcomp","kind":"trial","name":"RADCOMP","route":"/trials/radcomp/"}],"bottleneck":[{"id":"b-surgery-radiation-innovation","kind":"bottleneck","name":"Surgery and radiotherapy cure most, get least","route":"/bottlenecks/b-surgery-radiation-innovation/"}],"paper":[{"id":"paper-paganetti-proton-rbe-ijrobp-2014","kind":"paper","name":"Paganetti 2014: proton RBE is not a fixed 1.1","route":"/key-papers/paper-paganetti-proton-rbe-ijrobp-2014/"}],"roadmap":[{"id":"radiation-roadmap","kind":"roadmap","name":"Radiotherapy roadmap: X-rays → shaped beams → fewer fractions, particles and FLASH","route":"/roadmaps/radiation-roadmap/"}]}}