Study of improving IMRT dose accuracy in patients with metal implants by density filling and artifact reduction / 中华放射肿瘤学杂志

ABSTRACT

Objective:To explore the method of improving the accuracy of dose calculation of treatment plan in radiotherapy for patients with metal implants.Methods:A CT simulator with metal artifact reduction technique (MAR) was utilized to scan the CIRS intensity-modulated phantom with metal rods and 8 patients with steel nails implanted in the centrum for radiotherapy. Radiotherapy plans were designed using conventional CT images, MAR images and density-filled images. The dose calculation errors between single field and intensity-modulated radiotherapy (IMRT) plan were compared. The effect of mental implants and their artifacts on the irradiation dose of IMRT plan was evaluated.Results:In the conventional CT images of the phantom, when the incident path of the field failed to pass through the metal region, the dose calculation error for a single field was 3.85%, and the range of dose error for the field was 4.46%-74.11% when passing through the metal region. IMRT planning errors might exceed the clinically acceptable range when the incident path of the field passed through the metal region, and the errors tended to increase with the increase of dose weight of this field. After processing the images with density filling and artifact reduction techniques, the errors of the single field were 1.23% and 0.89%-4.73%, respectively, and the dose error of IMRT was 1.84%. The error of IMRT plan was 1.88% if density filling technique alone was employed to process the metal region. Due to the influence of metal implants and their artifacts, the minimum dose, average dose and prescription dose coverage actually received in the tumor target area were lower than IMRT plan results based on conventional CT images. The dosimetric difference of organs at risk was not statistically significant.Conclusions:In the radiotherapy plan based on conventional CT images, there may be a large dose calculation error when the incident path of field passes through the metal region. If the metal material is known, density filling of the metal region in the planning system can effectively improve the accuracy of dose calculation. Metal artifact reduction technique can significantly improve the image quality and further reduce dose calculation error, which should be a routine technique for CT machines equipped with this function to perform simulated localization of patients with metal implants.