Fast, high‐resolution 3D dosimetry utilizing a novel optical‐CT scanner incorporating tertiary telecentric collimation

Abstract

This study introduces a charge coupled device (CCD) area detector based optical-computed tomography (optical-CT) scanner for comprehensive verification of radiation dose distributions recorded in nonscattering radiochromic dosimeters. Defining characteristics include: (i) a very fast scanning time of ~5 min to acquire a complete three-dimensional (3D) dataset, (ii) improved image formation through the use of custom telecentric optics, which ensures accurate projection images and minimizes artifacts from scattered and stray-light sources, and (iii) high resolution (potentially 50 μm) isotropic 3D dose readout. The performance of the CCD scanner for 3D dose readout was evaluated by comparison with independent 3D readout from the single laser beam OCTOPUS™-scanner for the same PRESAGE™ dosimeters. The OCTOPUS™ scanner was considered the "gold standard" technique in light of prior studies demonstrating its accuracy. Additional comparisons were made against calculated dose distributions from the ECLIPSE treatment-planning system. Dose readout for the following treatments were investigated: (i) a single rectangular beam irradiation to investigate small field and very steep dose gradient dosimetry away from edge effects, (ii) a 2-field open beam parallel-opposed irradiation to investigate dosimetry along steep dose gradients, and (iii) a 7-field intensity modulated radiation therapy (IMRT) irradiation to investigate dosimetry for complex treatment delivery involving modulation of fluence and for dosimetry along moderate dose gradients. Dose profiles, dose-difference plots, and gamma maps were employed to evaluate quantitative estimates of agreement between independently measured and calculated dose distributions. Results indicated that dose readout from the CCD scanner was in agreement with independent gold-standard readout from the OCTOPUS™-scanner as well as the calculated ECLIPSE dose distribution for all treatments, except in regions within a few millimeters of the edge of the dosimeter, where edge artifact is predominant. Agreement of line profiles was observed, even along steep dose gradients. Dose difference plots indicated that the CCD scanner dose readout differed from the OCTOPUS™ scanner readout and ECLIPSE calculations by ~10% along steep dose gradients and by ~5% along moderate dose gradients. Gamma maps (3% dose-difference and 3 mm distance-toagreement acceptance criteria) revealed agreement, except for regions within 5 mm of the edge of the dosimeter where the edge artifact occurs. In summary, the data demonstrate feasibility of using the fast, high-resolution CCD scanner for comprehensive 3D dosimetry in all applications, except where dose readout is required close to the edges of the dosimeter. Further work is ongoing to reduce this artifact.

Application of Optical CT Scanning in Three-Dimensional Radiation Dosimetry

“…In theory, artifacts caused by the scattered light in optical CT scanners using a single laser source can be eliminated by reducing the detector apertures. In CCD-based optical CT scanners, telecentric lens can be used to select parallel beams from the scanned dosimeters (Krstajic and Doran, 2006;Sakhalkar and Oldham, 2008), thus minimizing the collection of the scattered light in the camera apertures.…”

“…The idea of optical CT was first introduced to gel dosimetry in 1996 together with a new tissue equivalent polymer gel dosimeter . Since then, optical CT scanners in a variety of forms have been built for imaging gel phantoms irradiated with photon, electron, proton beams as well as brachytherapy radiation sources (Islam et al, 2003;Wuu et al, 2003;Oldham and Kim, 2004;Xu et al, 2004;Doran et al, 2006;DeJean et al, 2006;Krstajic and Doran, 2006;Sakhalkar and Oldham, 2008;Olding et al, 2010). Currently, the advantage of the optical CT approach over other dose readout methods for gel dosimetry is commonly acknowledged (Oldham et al, 2001;Lopatiuk-Tirpak et al, 2008).…”

Large area, label-free imaging of extracellular matrix using telecentricity

“…We note that there were a few successful attempts to use telecentric lenses for optical computed and emission tomography. [7][8][9] However, the advantage of telecentric lenses for imaging highly anisotropic scattering medium, specifically biological tissue had not yet been explored systemically. Recently, we have proven the advantages of using telecentric lens for imaging through highly scattering media such as biological tissue.…”

Dosimetric comparison among different head and neck radiotherapy techniques using PRESAGE® dosimeter

“…Some studies presented that PRESAGE ® /Optical CT system had excellent precision, accuracy, reproducibility and robustness 3D dosimetry. [13][14] Recently, it is reported that ferrous xylenol-orange gel/optical-CT dosimetry system were used to demonstrate the feasibility of three dimensional dosimetry in RPC head and neck phantom. 15 Previous work has focused on the fundamental dosimetric characteristics of PRESAGE ® and investigation of the feasibility of the PRESAGE ® /optical CT system for 3D dosimetry.…”