Improvement of dose calculation in radiation therapy due to metal artifact correction using the augmented likelihood image reconstruction

Abstract

BackgroundMetal artifacts caused by high‐density implants lead to incorrectly reconstructed Hounsfield units in computed tomography images. This can result in a loss of accuracy in dose calculation in radiation therapy. This study investigates the potential of the metal artifact reduction algorithms, Augmented Likelihood Image Reconstruction and linear interpolation, in improving dose calculation in the presence of metal artifacts.Materials and MethodsIn order to simulate a pelvis with a double‐sided total endoprosthesis, a polymethylmethacrylate phantom was equipped with two steel bars. Artifacts were reduced by applying the Augmented Likelihood Image Reconstruction, a linear interpolation, and a manual correction approach. Using the treatment planning system Eclipse™, identical planning target volumes for an idealized prostate as well as structures for bladder and rectum were defined in corrected and noncorrected images. Volumetric modulated arc therapy plans have been created with double arc rotations with and without avoidance sectors that mask out the prosthesis. The irradiation plans were analyzed for variations in the dose distribution and their homogeneity. Dosimetric measurements were performed using isocentric positioned ionization chambers.ResultsIrradiation plans based on images containing artifacts lead to a dose error in the isocenter of up to 8.4%. Corrections with the Augmented Likelihood Image Reconstruction reduce this dose error to 2.7%, corrections with linear interpolation to 3.2%, and manual artifact correction to 4.1%. When applying artifact correction, the dose homogeneity was slightly improved for all investigated methods. Furthermore, the calculated mean doses are higher for rectum and bladder if avoidance sectors are applied.ConclusionStreaking artifacts cause an imprecise dose calculation within irradiation plans. Using a metal artifact correction algorithm, the planning accuracy can be significantly improved. Best results were accomplished using the Augmented Likelihood Image Reconstruction algorithm.

The application of metal artifact reduction methods on computed tomography scans for radiotherapy applications: A literature review

“…ALIR was studied by Ziemann et al 92 To simulate a pelvis with bilateral hip prostheses, a polymethylmethacrylate phantom with two SS rods was CT scanned. Then, ALIR, linear interpolation (LI), and density correction MAR methods were applied to create corresponding CT cor .…”

“…On clinical CT scans of a brain and H&N, the application of this proposed method improved the absolute ΔWET from 2.4 cm in brain and 1.7 cm in H&N to less than 2 mm for both cases. In a study by Nielsen et al, 84 ALIR was studied by Ziemann et al 92 To simulate a pelvis with bilateral hip prostheses, a polymethylmethacrylate phantom with two SS rods was CT scanned. Then, ALIR, linear interpolation (LI), and density correction MAR methods were applied to create corresponding CT cor .…”

MR‐based CT metal artifact reduction for head‐and‐neck photon, electron, and proton radiotherapy

“…This approximation is then expected to improve over the iterations Manual override techniques address the metal artifacts by visually replacing artifact‐corrupted regions with a bulk CT value. Since the oral cavity is largely water equivalent, a plausible CT value is 0 Hounsfield Units (HU), leading to a water override.…”

“…5,6 To potentially reduce dose calculation uncertainties, metal artifacts may be manually replaced with bulk CT values (typically water) by an experienced dosimetrist or similar, but this is time-consuming and subject to systematic bias and human error. 7,8 Alternatively, automatic metal artifact reduction (MAR) algorithms may be employed, typically supplied by the vendor of the CT scanner as a commercial add-on. Such vendor solutions must be scrutinized before clinical use to gauge their efficacy and possible limitations.…”

A New Phantom for Individual Verification of the Dose Distribution in Precision Radiotherapy for Head-and-Neck Cancer

“…Due to the fast development of rapid prototyping, it recently has become possible to produce phantoms that can take into account specific requirements for individual patients and can be produced at reasonable costs. The present study aimed to develop a new phantom specifically for head-and-neck cancer patients, which considers the impact of metal artifacts caused by dental fillings on the distribution of the radiation dose in these patients (9)(10)(11).…”