Genişletilmiş Bilgisayarlı Tomografi Skalası Ve Metal Artefakt Azalımı Yöntemlerinin İmplantlı Hastalarda Doz Dağılımına Etkisinin Bireyselleştirilmiş Fantomlar Kullanılarak Analiz Edilmesi

Abstract

Analysis of The Effects of Extended Computed Tomography Scale and Metal Artefact Reduction Methods on Dose Distribution of Patient with Implant by Using Individualized Fantoms. Hacettepe University Graduated School of Health Science, Msc. Thesis in Radiotheraphy Physics Program, Ankara, 2019. Today, the use of metal implants such as teeth, mandible, hip, and spine has become widespread in the human body. However, these implants cause artifacts in Computed Tomography (CT) imaging because of their high atomic number different from human tissue. Because radiotherapy (RT) treatment planning is done via CT images, these artifacts lead to uncertainties in RT dose calculations. The aim of this study was to investigate the effects of metal implants on the dose distribution in RT using three-dimensional (3D) individualized phantoms by placing Titanium (Ti) alloy implants and using their extended CT Scale (ECTS) and SEMAR (Single energy metal artefact reduction, Toshiba Medical Systems, Otowara, Japan) algorithms. First of all, implants are mounted on human bone shaped structures called sawbone and then placed in phantoms produced by 3D printing technology. In total, three phantoms and three implants were implanted. One of them is the mandible and the other two are cervical vertebra (C1-C3 and C4-C7) implants. After combining the phantoms, CT scans were performed on the Toshiba Aquilion LB BT (Toshiba Medical Systems, Otowara, Japan) and the GBTS and SEMAR methods were applied. For dosimetric measurements, EBT3 Gaphchromic films were placed on the appropriate sections of phantoms and irradiated in Varian Clinac DHX High Performance linear accelerator device. 2D dose maps obtained by film dosimetry were compared with 3DCRT and IMRT planning results from TPS. While evaluating the results of gamma analysis of the treatment plans, the four sets of criteria were used: 3% Dose Difference (DD) and 3 mm Distance to Agreement (DTA), 3% DD and 5 mm DTA, 5% DD and 3mm DTA, 5% DD and 5% DTA criteria were used. No significant differences were found in the measurements obtained from the mandible implant phantom. The reason for this is that it does not create enough artifacts due to its very thin and small structure. Gamma analysis results of GBTS method were better than standard CT scales (1-16%). There was no significant difference in the gamma analysis results of SEMAR method. As a result, it is recommended to use GBTS in the treatment of RT when implants create large metal artefacts. The SEMAR algorithm did not have a dosimetric effect in RT for defined conditions.