CT Simulation Phantom - Nuclear Associates Model 76-417

Radiation Therapy

CT Simulation Phantom

Nuclear Associates Model 76-417

Introduction

A CT simulator consists of a dedicated, fast

CT scanner (often a spiral scanner), a virtual

simulator (a set of computer software), and

a laser marking device to mark the center of

target volume. Therefore, methods of

designing and implementing quality control

procedures must include quality control on

each segment of the process. Accuracy of

table movements and lasers should also be

checked to be within 1 millimeter accuracy.

Quality control of a virtual simulator is a very

complex issue and difficult to verify, due to

the nature of software quality. Since

geometrical planning is the core of CT

simulation, periodic quality control is

essential for maintaining optimum image

quality and patient care. Hence, the quality

control of a virtual simulator consists of

testing every segment of the software for possible flaws. A detailed description of such a process

can be found in “A Practical Guide to CT Simulation.” 1,2 The basic features which must be

checked are reconstruction registration error (RRE), and geometrical accuracy in gantry, collimator

and table simulations. The test should also include imaging parameters such as low contrast

resolution and high contrast detectability of a DRR.

The CT Simulation Phantom tests all quality control

parameters that can affect patient treatment, including

RRE, magnification, image quality, and more

• For quality control of CT simulators

and treatment planning systems

capable of generating digitally

reconstructed radiographs

• Designed for use with spiral CT

scanners and may be used with

conventional scanners

• Simplifies quality control for the

radiology physicist and radiation

oncology physicist

• Verifies the accuracy of the digitally

reconstructed radiograph (DRR)

reconstruction for 3-D treatment

planning systems

Applications

Digitally reconstructed radiographs produced

from a commercial CT simulator have been

evaluated using this phantom which consists

of a 15 cm high-density polystyrene cubic

block. Polystyrene was chosen due to the

similarities in electron and physical densities

between it and water, while it’s dimensions

were chosen as a compromise between the

need to design a compact and portable

phantom and the desire to represent a typical

anatomical scan volume. In this instance, the

anatomical volume most representative of the

phantom can be considered as the head, the

neck and the brain.

The phantom contains four test patterns

engraved into three of its six faces. The four

patterns are designed to measure low and high

contrast resolution, modulation transfer

function, ray line divergence accuracy, and

spatial linearity of the digitally reconstructed

radiograph.

Various 3-D treatment planning systems can

also generate DRR. Hence, the quality control

of DRR generation needs to be addressed. This

versatile phantom provides essential quality

control tools for geometrical 3-D treatment

planning systems and imaging tools for CT-

simulation as well, which are capable of

generating DRR for portal design.

Specifications

Material Acrylic

Dimensions 5.906 x 5.906 in (15 x 15 cm)

Weight 9.24 lb (4.19 kg)

Available model(s)

76-417 CT Simulation Phantom

References

1. K.P., McGee, I.J. Das, “Commissioning Acceptance

Testing and Quality Assurance of a CT Simulator,” in

A Practical Guide to CT Simulation ,” L.R. Coia, T.E.

Schultheiss, and G.E. Hanks, eds. (Madison, WI.:

Advanced Medical Publishing, 1995), 39-50.

2. K.P., McGee, I.J. Das, C. Sims, “Evaluation of

Digitally Reconstructed Radiographs (DRRs) Used for

Clinical Radiotherapy: A Phantom Study,” Medical

Physics , 22 (1995),1815-1827. Request Reprint No.

638B.

Schematic representation of the phantom developed to

evaluate DRRs: (a) Top face of the DRR phantom showing

the contrast-detail, MTF, ray line divergence (RLD), and

spatial linearity (SL) test patterns. (b) Side face of the

phantom showing the MTF and SL test pattern. (c) shows

the third face of the phantom containing the RLD pattern.

The two lines represent the rods embedded at distances of

5.38 and 6.25 cm from the central axis of the phantom