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How many grays of ordinary X-rays you would need to match the damage from one gray of this radiation. Protons are treated as 1.1 times as damaging as X-rays; that number is a convention, and the true value is higher where the beam stops.
Relative biological effectiveness is the photon dose divided by the particle dose that produces the same biological effect. Clinical proton therapy reports dose as Gy(RBE) using a constant 1.1 (ICRU 78). Laboratory and modelling work show RBE rising above 1.1 at the distal edge, where linear energy transfer is highest, which can put extra biological dose in tissue just beyond the target. Carbon-ion therapy uses higher, model-dependent RBE (often around 2 to 3; local effect model or microdosimetric kinetic model). RBE depends on endpoint, dose per fraction, and the tissue's alpha/beta ratio: late-responding tissues with low alpha/beta are more sensitive to high-LET increments. Constant 1.1 is a reporting rule, not a measurement.
Showing the technology this term belongs to: Proton therapy.
For men with low- or intermediate-risk prostate cancer, protons and modern IMRT give the same excellent quality of life and cancer control, so the choice can rest on access, cost and convenience rather than on an expected sparing of bowel or bladder. The result removes prostate cancer from the list of adult indications where a proton advantage was assumed but untested.
A proton plan that looks safe on a 1.1 RBE map can still over-dose a late-responding organ sitting on the distal edge. Comparing protons with IMRT without an LET-weighted view asks the wrong physical question.
Two term pages on OnCo cite this paper by its DOI; this record gives the citation a page of its own so a reader can follow it without leaving OnCo. Read the abstract above alongside the citing pages listed under Related; the record was created automatically from the Europe PMC entry and its figures have not been checked by hand.
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Shares Oxygen enhancement ratio, Linear energy transfer (LET), Radiotherapy roadmap: X-rays → shaped beams → fewer fractions, particles and FLASH.
Shares Pooled coverage-with-evidence for proton therapy across all centres, Carbon-ion therapy, Proton therapy.
Shares PARTIQoL: phase 3 randomised trial of proton therapy versus IMRT for localised prostate cancer (ASTRO 2024 late-breaking abstract), Proton therapy, IMRT / IGRT (modern external beam).
Shares Pooled coverage-with-evidence for proton therapy across all centres, Radiotherapy roadmap: X-rays → shaped beams → fewer fractions, particles and FLASH, Proton therapy.
Shares Carbon-ion therapy, Radiotherapy roadmap: X-rays → shaped beams → fewer fractions, particles and FLASH, Proton therapy.