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Conversion of CT numbers into tissue parameters for Monte Carlo dose calculations: a multi-centre study

2007; IOP Publishing; Volume: 52; Issue: 3 Linguagem: Inglês

10.1088/0031-9155/52/3/001

1361-6560

Barbara Vanderstraeten, M. Chin, Michael K. Fix, Antonio Leal, G. Mora, N. Reynaert, Joao Seco, Martin Soukup, Emiliano Spezi, Wilfried De Neve, Hubert Thierens,

Radiation Dose and Imaging

The conversion of computed tomography (CT) numbers into material composition and mass density data influences the accuracy of patient dose calculations in Monte Carlo treatment planning (MCTP). The aim of our work was to develop a CT conversion scheme by performing a stoichiometric CT calibration. Fourteen dosimetrically equivalent tissue subsets (bins), of which ten bone bins, were created. After validating the proposed CT conversion scheme on phantoms, it was compared to a conventional five bin scheme with only one bone bin. This resulted in dose distributions D 14 and D 5 for nine clinical patient cases in a European multi-centre study. The observed local relative differences in dose to medium were mostly smaller than 5%. The dose–volume histograms of both targets and organs at risk were comparable, although within bony structures D 14 was found to be slightly but systematically higher than D 5 . Converting dose to medium to dose to water (D 14 to D 14wat and D 5 to D 5wat ) resulted in larger local differences as D 5wat became up to 10% higher than D 14wat . In conclusion, multiple bone bins need to be introduced when Monte Carlo (MC) calculations of patient dose distributions are converted to dose to water.