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SU‐E‐T‐603: Dosimetric Impact of Low‐Z vs. High‐Z Metal Implants on IMRT Treatments
Author(s) -
Spadea M,
Verburg J,
Baroni G,
Seco J
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612565
Subject(s) - imaging phantom , nuclear medicine , radiation treatment planning , artifact (error) , medicine , radiation therapy , biomedical engineering , radiology , computer science , computer vision
Purpose: To evaluate the dosimetric impact of low‐Z and high‐Z metallic implants on dose calculation for IMRT treatment.Methods: A phantom and three patients with various metallic implants were studied. Two of the patients had titanium (ρ=4.54 g/cm3) spinal hardware and dental fillings. The third patient received vascular embolization with platinum coiling (ρ=21.45 g/cm3) in the brain. The phantom was filled with two low density (titanium) and two high‐density inserts (Cerrobend, ρ=9.76 g/cm3, to mimic high‐Z implants used in patients). IMRT plans were designed and optimized on the original images. A sinogram‐ based metal artifact reduction (MAR) algorithm was applied to correct the simulation CT images. Dose calculations were then performed on both the original and corrected images using XiO (Elekta) and an in‐house Monte Carlo platform. To assess the dosimetric impact of the artifacts, the DVHs of the clinical target volumes were analyzed.Results: The evaluation of DVHs indicates that high‐density materials compromise IMRT dose calculations when metal streak artifacts are present in the beam path. In the phantom study with high‐density implants, dose errors of 6% were observed at 95% isodose of the target DVH. In case of titanium, the error was 0.4%. In the patient plans, errors of 3–6% occurred due to platinum coiling, while titanium hardware resulted in a limited error of 0.2% Conclusions: Better metal artifact reduction methods are becoming available and allow for improved CT image quality for radiotherapy planning and dose calculation. Besides the evident improvement for volume of interest visualization and contouring, the physical characteristics of metal material mainly influence the dose error computation in streaked regions of the CT image. Our conclusion is that dose calculation is not always jeopardizes by metal presence. However, in case of high‐density materials MAR correction is necessary to improve the accuracy of treatment planning. This work was partly supported by The Fulbright Program, sponsored by the U.S. Department of Stateˈs Bureau of Education and Cultural Affairs