Relationship between CT number and electron density, scatter angle and nuclear reaction for hadron-therapy treatment planning

Abstract

The precise conversion of CT numbers to their electron densities is essential in treatment planning for hadron therapy. Although some conversion methods have already been proposed, it is hard to check the conversion accuracy during practical therapy. We have estimated the CT numbers of real tissues by a calculational method established by Mustafa and Jackson. The relationship between the CT numbers and the electron densities was investigated for various body tissues as well as some tissue-equivalent materials used for a conversion to check the accuracy of the current conversion methods. The result indicates a slight disagreement at the high-CT-number region. A precise estimation of the multiple scattering, nuclear reaction and range straggling of incident particles has been considered as being important to realize higher-level conformal therapy in the future. The relationship between these parameters and the CT numbers was also investigated for tissues and water. The result shows that it is sufficiently practical to replace these parameters for real tissues with those for water by adjusting the density.

A CT calibration method based on the polybinary tissue model for radiotherapy treatment planning

“…However, those artificial materials might not sufficiently be equivalent to the real tissues for charged particle radiotherapy, where very accurate depth control is required. Schneider et al (1996) and Matsufuji et al (1998) estimated the inaccuracy with the tissue-substitute calibration to a few percent in effective density. Rietzel et al (2000) used real animal tissues to resolve the problem, though measurements of various raw tissues with CT and therapeutic beams in the identical condition may be technically difficult in practice.…”

Scanned Ion Beam Therapy of Moving Targets with Beam Tracking

“…Accuracy and its speed of the range shift depend on the specified range shift (approximately 1 mm WE deviation for 5 mm WE range shift in 10 ms), and it shows better accuracy for a slower scan speed (Saito, Bert, Chaudhri, Gemmel, Schardt, & Rietzel 2009b). The accuracy of the range adaptation is comparable to the uncertainties of CT data conversion to ion ranges (Jäkel et al 2001;Matsufuji et al 1998;Rietzel et al 2007). A photo of the current implementation of the range shifter is shown in figure 4 together with motion detection device and a motion phantom with a robotic arm.…”

MRI based radiotherapy planning and pulse sequence optimization

“…Conversion from arbitrary Hounseld units to electron density can be done using semi-empirical formulas [20,37] or via a tissue look up table [33,34]. Proton and ion beams interact with tissue in a variety of ways, each with a dierent relationship to the material characteristics obtained from CT [47]. This implies that for protons and ions, the ability to precisely dene tissues based on CT scans has a signicant impact on the accuracy of dose calculations [36,58].…”