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The spot where a proton or carbon-ion beam dumps most of its energy and then stops, so tissue behind the tumour gets almost no dose.
A charged particle slows as it travels through tissue and deposits most of its energy in a narrow peak just before it stops. That Bragg peak is why protons and carbon ions have no exit dose compared with X-rays. The spread-out Bragg peak stacks several energies to cover a tumour's depth. Linear energy transfer, and therefore relative biological effectiveness, is highest at the distal edge of the peak, which is why a constant proton RBE of 1.1 can understate dose just beyond the target. Range uncertainty of a few millimetres is the planning counterpart of that edge.
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.
Shares PARTIQoL: phase 3 randomised trial of proton therapy versus IMRT for localised prostate cancer (ASTRO 2024 late-breaking abstract), RADCOMP, PARTIQoL, Caution: proton therapy vs IMRT.
Shares Paganetti 2014: proton RBE is not a fixed 1.1, PARTIQoL, Caution: proton therapy vs IMRT, Relative biological effectiveness (RBE).
Shares Caution: proton therapy vs IMRT, Relative biological effectiveness (RBE), Linear energy transfer (LET), Use LET, RBE and alpha/beta to decide when protons beat IMRT.
Shares Relative biological effectiveness (RBE), Linear energy transfer (LET), Carbon-ion therapy.
Shares Relative biological effectiveness (RBE), Linear energy transfer (LET).
Shares Relative biological effectiveness (RBE), Use LET, RBE and alpha/beta to decide when protons beat IMRT, Proton therapy.
Shares PARTIQoL: phase 3 randomised trial of proton therapy versus IMRT for localised prostate cancer (ASTRO 2024 late-breaking abstract), Proton therapy.
Shares Proton arc therapy, Proton therapy.