Reassessment of stopping power ratio uncertainties caused by mean excitation energies using a water‐based formalism

• DOI: 10.1002/mp.12949
• Publication Date: 2018-05-05T01:17:13Z
• Authors: Valérie De Smet; Rudi Labarbe; François Vander S...; Benoît Macq; Edmond Sterpin
• Keywords: Additive function; Stopping power; Mass fraction

In proton therapy planning, the accuracy of Stopping Power Ratios (SPR) calculated in stoichiometric CT calibration is affected by, among others, uncertainties on mean excitation energies (I-values) human tissues and water. Traditionally, contribution these SPR has been conservatively estimated order 1% or more for a reference tissue known composition. This study provides methodology that enables finer estimation this uncertainty, eventually showing traditional estimates uncertainty are too conservative.Since contain water, correlation exists between I-values As ratio stopping power to decreases SPR. Our formalism considers by expressing I-value as function water weight fraction while applying Bragg's additivity rule only nonaqueous mixture tissue. For 22 compositions, was randomly sampling Gaussian distributions, based ICRU data, mixture, well fraction.The relative standard deviation SPR, at 150 MeV, range 0.1%-0.3% soft with an average percentage least 60%. low content (e.g., adipose bones), 0.5%-0.7%.Uncertainties appear have significantly lower impact than traditionally expected. future, may provide rationale using smaller distal proximal margins target volume, provided all other components correctly too.