Revision 1

Superseded · first revision · record

Title: Which ion species is optimal for therapy
Plain: Beyond protons, beams of helium, carbon, oxygen and neon are possible, each with a different balance of sharpness, biological effect and unwanted fragments. Which one is best for which tumour is unsettled.
Precise: Rank ion species by atomic number Z from 1 to 10 against the combined criteria of lateral and distal penumbra, dose-averaged LET in target versus normal tissue, fragmentation tail dose beyond the Bragg peak, and oxygen enhancement ratio in hypoxic targets. An answer is a classification of tumour and site classes to the preferred ion, with the physics criteria that decide each case.
Settled by: Comparative planning plus measured fragmentation yields and in vivo effectiveness for each species on a common endpoint set.
Kind: well-posed
Answer type: classification
References: (empty)
Literature status: open
Status note: Helium returned to clinical use at HIT Heidelberg in 2021, after the Berkeley helium programme of 1957 to 1992; oxygen and multi-ion schemes were under study in 2025 without a settled ranking.
Posed since: 1975