Revision 1

Superseded · first revision · record

Title: Beam-quality factors and $W_{\mathrm{air}}$ for ion dosimetry
Plain: Converting a detector reading into dose in a particle beam needs the average energy spent to make one ion pair in air. Its uncertainty, especially for carbon ions, dominates the dose error.
Precise: Reduce the uncertainty in the mean energy per ion pair in air $W_{\mathrm{air}}$ and in the beam-quality correction factor $k_Q$ for carbon and other ions to the level needed for a total dosimetric uncertainty below $1.5\,\mathrm{percent}$. ICRU 90 values are $W_{\mathrm{air}}$ of about $34.44\,\mathrm{eV}$ for protons (about $0.4\,\mathrm{percent}$ standard uncertainty) and $34.71\,\mathrm{eV}$ for carbon ions (about $1.5\,\mathrm{percent}$). An answer is a measured value set with reduced uncertainty.
Settled by: Calorimetric determination of $W_{\mathrm{air}}$ and $k_{Q}$ in clinical ion beams.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: partially-resolved
Status note: IAEA TRS-398 Rev. 1 (2024) adopted the ICRU 90 data; for carbon ions the $W_{\mathrm{air}}$ and $k_{Q}$ terms still keep the total uncertainty near 3 percent.
Posed since: 1990