Alifiani, Rustika (2026) Evaluasi Pengaruh Deviasi Isocenter Terhadap Akurasi Dosis pada Mata Menggunakan Fantom Antropomorfik 3D dalam Perencanaan IMRT untuk Kanker Nasofaring. Masters thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Kanker nasofaring merupakan salah satu kanker kepala-leher dengan angka kejadian tinggi di Asia Tenggara, termasuk Indonesia, dengan radioterapi menjadi modalitas utama terapinya. Teknik Intensity-Modulated Radiation Therapy (IMRT) memungkinkan distribusi dosis konformal pada target, namun akurasinya bergantung pada ketepatan posisi isocenter sebagai titik acuan utama seluruh sistem penyinaran menggunakan linear accelerator (Linac). Deviasi isocenter akibat kesalahan mekanik, sistem laser, atau posisi pasien berpotensi mengubah distribusi dosis sehingga menurunkan cakupan dosis pada Planning Target Volume (PTV) dan meningkatkan dosis pada organ sensitif, seperti mata. Penelitian ini bertujuan mengevaluasi pengaruh deviasi isocenter terhadap akurasi dosis pada mata. Penelitian dilakukan menggunakan tiga fantom kepala-leher spesifik berbahan polylactic acid (PLA) berbasis data Computed Tomography (CT) pasien. Perencanaan penyinaran IMRT menggunakan Treatment Planning System (TPS) Monaco dengan sumber foton 6 MV, serta penyinaran menggunakan pesawat Linac Elekta. Deviasi isocenter dilakukan pada sumbu Z dengan rentang 1–5 mm. Analisis dilakukan menggunakan parameter Dose Volume Histogram (DVH), gamma passing rate (GPR) dengan kriteria 3%/3 mm, 3%/2 mm, dan 2%/2 mm, serta verifikasi dosis pada lensa, bola mata, dan saraf optik menggunakan film Gafchromic EBT4. Hasil penelitian menunjukkan bahwa peningkatan deviasi isocenter menyebabkan penurunan cakupan dosis pada PTV dan peningkatan dosis pada organ mata. Nilai GPR menurun seiring bertambahnya deviasi isocenter, khususnya pada kriteria gamma yang lebih ketat. Rencana dengan kompleksitas dosis tinggi menunjukkan sensitivitas yang lebih besar terhadap deviasi isocenter. Verifikasi dosis menggunakan film Gafchromic EBT4 menunjukkan kesesuaian yang baik dengan TPS pada kondisi deviasi kecil, namun perbedaan dosis meningkat pada deviasi yang lebih besar. Dengan demikian, deviasi isocenter berpengaruh signifikan terhadap akurasi distribusi dosis IMRT, sehingga ketelitian penentuan isocenter menjadi faktor penting dalam menjaga kualitas dan keamanan terapi. Oleh karena itu, toleransi deviasi isocenter ≤ 1 mm direkomendasikan untuk menjaga akurasi dosis pada PTV dan meminimalkan peningkatan dosis pada organ mata, sesuai dengan rekomendasi American Association of Physicists in Medicine (AAPM) TG-142.
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Nasopharyngeal cancer is one of the most common head and neck cancers in Southeast Asia, including Indonesia, with radiotherapy being the main treatment modality. Intensity-Modulated Radiation Therapy (IMRT) allows for conformal dose distribution to the target, but its accuracy depends on the precision of the isocenter position as the main reference point for the entire irradiation system using a linear accelerator (Linac). Isocenter deviation due to mechanical errors, laser system errors, or patient positioning has the potential to alter dose distribution, thereby reducing dose coverage in the Planning Target Volume (PTV) and increasing the dose to sensitive organs, such as the eyes. This study aims to evaluate the effect of isocenter deviation on dose accuracy in the eyes. The study was conducted using three specific head-and-neck phantoms made of polylactic acid (PLA) based on patient Computed Tomography (CT) data. IMRT radiation planning was performed using the Monaco Treatment Planning System (TPS) with a 6 MV photon source, and radiation was delivered using an Elekta Linac. Isocenter deviation was performed on the Z-axis with a range of 1–5 mm. Analysis was performed using the Dose Volume Histogram (DVH) parameter, gamma passing rate (GPR) with criteria of 3%/3 mm, 3%/2 mm, and 2%/2 mm, as well as dose verification on the lens, eyeball, and optic nerve using Gafchromic EBT4 film. The results showed that an increase in isocenter deviation caused a decrease in dose coverage in the PTV and an increase in dose to the eye. The GPR value decreased as isocenter deviation increased, particularly for stricter gamma criteria. Plans with high dose complexity showed greater sensitivity to isocenter deviation. Dose verification using Gafchromic EBT4 film showed good agreement with the TPS under small deviation conditions, but dose differences increased with larger deviations. Thus, isocenter deviation significantly affects the accuracy of IMRT dose distribution, making the precision of isocenter determination an important factor in maintaining the quality and safety of therapy. Therefore, an isocenter deviation tolerance of ≤ 1 mm is recommended to maintain dose accuracy in the PTV and minimize dose increases in the eye, in accordance with the recommendations of the American Association of Physicists in Medicine (AAPM) TG-142.
| Item Type: | Thesis (Masters) |
|---|---|
| Uncontrolled Keywords: | Deviasi Isocenter, DVH, Gafchromic EBT4, Gamma Index, IMRT, Radioterapi DVH, Gafchromic EBT4, Gamma Index, IMRT, Isocenter Deviation, Radioterapi |
| Subjects: | Q Science > QC Physics > QC795.5 Radioactivity and radioactive Instruments and apparatus (General) |
| Divisions: | Faculty of Science and Data Analytics (SCIENTICS) > Physics > 45101-(S2) Master Thesis |
| Depositing User: | Rustika Alifiani |
| Date Deposited: | 04 Feb 2026 06:17 |
| Last Modified: | 04 Feb 2026 06:17 |
| URI: | http://repository.its.ac.id/id/eprint/132003 |
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