Table 2.

Fitting parameters of α and p for various materials when applying the BK rule. The energies used in the fit were from 10 to 250 MeV for proton beams, 25 to 1000 MeV for helium ions, and 250 to 10 000 MeV for carbon ions and iron ions.

	Proton		Helium		Carbon		Iron
Material	α	p	α	p	α	p	α	p
Lung	8.994 × 10−3	1.735	7.420 × 10−4	1.748	1.908 × 10−4	1.545	8.421 × 10−7	1.715
HDPE	2.541 × 10−3	1.737	2.380 × 10−4	1.738	5.352 × 10−5	1.548	2.337 × 10−7	1.719
Water	2.633 × 10−3	1.735	2.367 × 10−4	1.735	5.605 × 10−5	1.545	2.443 × 10−7	1.716
Polystyrene	2.545 × 10−3	1.735	2.285 × 10−4	1.736	5.378 × 10−5	1.546	2.314 × 10−7	1.719
PMMA	2.271 × 10−3	1.735	2.039 × 10−4	1.736	4.814 × 10−5	1.545	2.161 × 10−7	1.714
Lexan	2.310 × 10−3	1.735	2.067 × 10−4	1.736	4.838 × 10−5	1.546	2.145 × 10−7	1.716
Bone substitute	1.666 × 10−3	1.730	1.502 × 10−4	1.731	3.566 × 10−5	1.540	1.543 × 10−7	1.714
Aluminum	1.364 × 10−3	1.719	1.257 × 10−4	1.719	2.897 × 10−5	1.534	1.432 × 10−7	1.694
Titanium	9.430 × 10−4	1.710	8.721 × 10−5	1.712	1.949 × 10−5	1.531	1.084 × 10−7	1.679
Stainless steel	5.659 × 10−4	1.706	5.159 × 10−5	1.707	1.173 × 10−5	1.525	6.273 × 10−8	1.678
Lead	6.505 × 10−4	1.676	6.357 × 10−5	1.676	1.438 × 10−5	1.499	7.887 × 10−8	1.656
Gold	3.705 × 10−4	1.677	3.628 × 10−5	1.677	8.053 × 10−6	1.502	5.495 × 10−8	1.633