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KMID : 1164220190310010025
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Journal of Korean Society for Radiotherapeutic Technology
2019 Volume.31 No. 1 p.25 ~ p.32
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Evaluation of Metal Volume and Proton Dose Distribution Using MVCT for Head and Neck Proton Treatment Plan
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Seo Sung-Gook
Kwon Dong-Yeol
Park Sey-Joon
Park Yong-Cheol
Choi Byeong-Ki
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Abstract
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Purpose : The size, shape, and volume of prosthetic appliance depend on the metal artifacts resulting from dental implant during head and neck treatment with radiation. This reduced the accuracy of contouring targets and surrounding normal tissues in radiation treatment plan. Therefore, the purpose of this study is to obtain the images of metal representing the size of tooth through MVCT, SMART-MAR CT and KVCT, evaluate the volumes, apply them into the proton therapy plan, and analyze the difference of dose distribution.
Materials and Methods : Metal A (0.5×0.5×0.5 cm), Metal B (1×1×1 cm), and Metal C (1×2×1 cm) similar in size to inlay, crown, and bridge taking the treatments used at the dentist’s into account were made with Cerrobend (9.64 g/cm3). Metal was placed into the In House Head & Neck Phantom and by using CT Simulator (Discovery CT 590RT, GE, USA) the images of KVCT and SMART-MAR were obtained with slice thickness 1.25 mm. The images of MVCT were obtained in the same way with RADIXACT® Series (Accuracy Precision®, USA). The images of metal obtained through MVCT, SMART-MAR CT, and KVCT were compared in both size of axis X, Y, and Z and volume based on the Autocontour Thresholds Raw Values from the computerized treatment planning equipment Pinnacle (Ver 9.10, Philips, Palo Alto, USA). The proton treatment plan (Ray station 5.1, RaySearch, USA) was set by fusing the contour of metal B (1×1×1 cm) obtained from the above experiment by each CT into KVCT in order to compare the difference of dose distribution.
Result : Referencing the actual sizes, it was appeared: Metal A (MVCT: 1.0 times, SMART-MAR CT: 1.84 times, and KVCT: 1.92 times), Metal B (MVCT: 1.02 times, SMART-MAR CT: 1.47 times, and KVCT: 1.82 times), and Metal C (MVCT: 1.0 times, SMART-MAR CT: 1.46 times, and KVCT: 1.66 times). MVCT was measured most similarly to the actual metal volume. As a result of measurement by applying the volume of metal B into proton treatment plan, the dose of D 99 % volume was measured as: MVCT: 3094 CcGE, SMART-MAR CT: 2902 CcGE, and KVCT: 2880 CcGE, against the reference 3082 CcGE.
Conclusion : Overall volume and axes X and Z were most identical to the actual sizes in MVCT and axis Y, which is in the superior-Inferior direction, was regular in length without differences in CT. The best dose distribution
was shown in MVCT having similar size, shape, and volume of metal when treating head and neck protons. Thus it is thought that it would be very useful if the contour of prosthetic appliance using MVCT is applied into KVCT for proton treatment plan.
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KEYWORD
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Dental Implant, Metal Artifact, SMART-MAR, MVCT, Proton
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