The objective of this work is to study the influence of the patient size and geometry on CBCT Hounsfield Unit and the accuracy of calibration Hounsfield Unit to electron density (HU-ED) using patient specific HU-ED mapping method for dose calculation. Two clinical cases, namely nasopharyngeal carcinoma (NPC) case and prostate case for 4 patients with different size and geometry were enrolled to assess the impact of size and geometry on CBCT Hounsfield Unit. The accuracy of the patient specific HU-ED mapping method was validated by comparing dose distributions based on planning CT and CBCT, dose-volume based indices and the digitally reconstructed radiograph (DRR) by analyzing their line profile plots. Significant differences in Hounsfield unit and line profile plots were found for NPC and prostate cases. The doses computed based on planning CT data sets and CBCT datasets for both clinical cases agree to within 1% for planning target volumes and 3% for organs at risk. The data shows that there are high dependence of HU on patient size and geometry; thus, the use of one CBCT HU-ED calibration curve made of one size and geometry will not be accurate for use with a patient of different size and geometry.
Kejituan persediaan rawatan dengan teknik yang kesamabentukannya tinggi seperti terapi isi padu arka termodulat (VMAT) berupaya mengurangkan dedahan dos sinaran yang berlebihan di bahagian mukosa oral. Oleh itu, satu kajian telah dijalankan untuk meningkatkan kejituan persediaan rawatan antara-pecahan rawatan dengan mengenal pasti penggunaan peranti cegah gerak yang sesuai. Seramai dua belas pesakit kanser mulut terlibat dalam kajian ini. Mereka dikategorikan kepada tiga kumpulan yang menggunakan peranti cegah gerak yang berbeza; HFW: headFIX ® mouthpiece dibentuk dengan lilin, SYR: 10 cc / ml picagari dan TDW: lilin dibentuk pada kayu penekan lidah. Sebelum rawatan diberikan, pesakit menjalani radioterapi berpandukan imej (IGRT) bagi pengukuran ralat persediaan rawatan posisi. Sejumlah 292 set imej tomografi berkomputer bim-kon (CBCT) diperolehi. Perbezaan pada translasi (lateral, longitudinal, vertikal) dan rotasi (pic, guling, rewang) dalam setiap imej CBCT ditentukan. Ralat posisi pesakit dianalisis untuk aliran masa sepanjang radioterapi. Pengiraan ralat sistematik (Σ) dan rawak (σ) dilakukan dan margin CTV-PTV ditentukan. Min ± SD bagi ralat persediaan rawatan mutlak untuk HFW adalah paling rendah (p < 0.001) untuk semua ralat translasi
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