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. Author manuscript; available in PMC: 2007 Apr 26.
Published in final edited form as: J Phys Conf Ser. 2006 Dec 1;56(1):191–194. doi: 10.1088/1742-6596/56/1/025

Quality assurance in 3D dosimetry by optical-CT

Pengyi Guo 1, John Adamovics 2, Mark Oldham 3
PMCID: PMC1857335  NIHMSID: NIHMS19832  PMID: 17464369

1. Introduction

A promising new system for 3D dosimetry combines a radiochromic plastic dosimeter, PRESAGE [1–3], with an optical-computed-tomography system (optical-CT) capable of reading the dose recorded in the dosimeter [4,5]. Optical-CT is also the method of choice for reading out the dose recorded in the more established polymer gel dosimetry system, for many applications [6–9]. Achieving accurate dosimetry depends critically on the performance characteristics of the optical-CT imaging system. Several systems have been developed [6,10–12], and two are commercially available at the present time (MGS Research Inc, and Modus Medical Devices Inc). Common issues of quality assurance (QA) become significant for all these systems to ensure correct initial commissioning of optical-CT 3D dosimetry and correct continued functioning. Here we present a QA phantom and procedure designed for efficient evaluation of the basic imaging performance of any optical-CT scanning system. Example results are presented from two optical-CT systems, an in-house CCD based system and the OCTOPUS™ system from MGS Research.

2. Methods

The optical-CT QA phantom consists of a ‘layer cake’ model (figure 1) where each layer contains special features designed to test different aspects of the imaging system. The phantom is constructed out of polyurethane and contains a range of inserts. It is also constructed to be optically stable in time, so that repetitious scanning yields information on the temporal stability of the scanning system.

Figure 1.

Figure 1

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a) Schematic of the optical-CT QA phantom, and photographs of the optical-CT QA phantom b) top view and c) side view

3. Results

Sample images of select layers of the optical-CT QA phantom and derived imaging performance obtained with the OCTOPUS™ scanner are shown in figure 2 to 4. Good geometrical accuracy (within 0.5 mm) and linearity of reconstructed attenuation coefficients (r2 = 0.9917 in figure 4a) were observed.

Figure 2.

Figure 2

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Contrast-Detail layer

Figure 4.

Figure 4

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a) linearity of attenuation coefficients, b) point-spread-function (uncorrected for wire diameter).

4. Conclusions

The optical-CT QA phantom presented here represents an important development for ensuring correct implementation and ongoing performance of an optical-CT scanning system. Our initial results with the OCTOPUS scanning system from MGS Inc are encouraging. Repeat scanning has revealed excellent consistency of performance over many months.

Figure 3.

Figure 3

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Geometrical accuracy layer

Contributor Information

Pengyi Guo, Dept of Radiation Oncology, Duke University Medical Center, Durham, NC, USA.

John Adamovics, Dept of Chemistry and Biology, Rider University, Lawrenceville, NJ, USA.

Mark Oldham, Dept of Radiation Oncology, Duke University Medical Center, Durham, NC, USA.

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