A fast dual wavelength laser beam fluid-less optical CT scanner for radiotherapy 3D gel dosimetry I: design and development

Abstract

Three dimensional dosimetry by optical CT readout of radiosensitive gels or solids has previously been indicated as a solution for measurement of radiotherapy 3D dose distributions. The clinical uptake of these dosimetry methods has been limited, partly due to impracticalities of the optical readout such as the expertise and labour required for refractive index fluid matching. In this work a fast laser beam optical CT scanner is described, featuring fluid-less and dual wavelength operation. A second laser with a different wavelength is used to provide an alternative reference scan to the commonly used pre-irradiation scan. Transmission data for both wavelengths is effectively acquired simultaneously, giving a single scan process. Together with the elimination of refractive index fluid matching issues, scanning practicality is substantially improved. Image quality and quantitative accuracy were assessed for both dual and single wavelength methods. The dual wavelength scan technique gave improvements in uniformity of reconstructed optical attenuation coefficients in the sample 3D volume. This was due to a reduction of artefacts caused by scan to scan changes. Optical attenuation measurement accuracy was similar for both dual and single wavelength modes of operation. These results established the basis for further work on dosimetric performance.

Validation of complex radiotherapy techniques using polymer gel dosimetry

“…A substantial inconvenience to the configurations shown in figure 3(d) is the need for refractively matched fluid bath. Several studies have explored ways to eliminate (or greatly reduce) this inconvenience (Ramm et al 2012, Bache et al 2016, Ramm 2018). In addition several groups have developed useful optical simulation softwares to explore scanning configurations and artifact formation and reduction (Oldham 2010, Adamson et al 2014, Chisholm et al 2015.…”

A fast dual wavelength laser beam fluid-less optical CT scanner for radiotherapy 3D gel dosimetry II: dosimetric performance

“…Measurement accuracy would be ideally at least comparable to accepted measurement methods such as film dosimetry. Advances towards a clinical true 3D dosimetry system with a fluid-less dual wavelength optical CT (FDOCT) were made in the companion paper for this work (Ramm 2018), hereafter referred to as Part I. The FDOCT scanner features a plastic cylinder containing a gel dosimeter that is placed on the scanner without the complications of immersing the dosimeter in refractive index (RI) matching fluid like other scanners (Doran 2013).…”