Analisis Pengaruh Pergeseran Isocenter terhadap Dosimetri dan Radiobiologi pada Kanker Nasofaring Menggunakan Teknik Volumetric Modulated Arc Therapy (VMAT)

Zahara, Yessa Gresianatasa (2026) Analisis Pengaruh Pergeseran Isocenter terhadap Dosimetri dan Radiobiologi pada Kanker Nasofaring Menggunakan Teknik Volumetric Modulated Arc Therapy (VMAT). Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Kanker nasofaring merupakan salah satu kanker yang umumnya ditangani dengan radioterapi, khususnya teknik Volumetric Modulated Arc Therapy (VMAT) yang mampu memberikan distribusi dosis presisi. Namun, deviasi isocenter akibat ketidakpastian posisi pasien dapat mempengaruhi akurasi dosis dan respon radiobiologi. Penelitian ini bertujuan menganalisis pengaruh pergeseran pasien pada isocenter terhadap parameter dosimetri dan radiobiologi. Penelitian ini menggunakan simulasi planning pada TPS dengan data sekunder dari 10 pasien dianalisis dengan simulasi pergeseran sebesar ±1, ±2, dan ±3 mm pada sumbu-X (lateral) dan sumbu-Y (longitudinal), menghasilkan 130 data. Parameter yang dievaluasi meliputi distribusi dosis pada PTV dan OAR serta HI, CI, TCP, dan NTCP. Hasil menunjukkan D2% tidak menghasilkan hotspot pada seluruh kondisi pergeseran (p > 0,05), sedangkan D98% menurun signifikan (p = 0,005) menyebabkan underdose di bawah 95% dosis preskripsi terutama pada pergeseran ±3 mm. Nilai HI meningkat hingga 0,18 dan CI menurun hingga 0,85 dengan degradasi terbesar pada pergeseran sumbu-Y. TCP menurun proporsional terhadap penurunan EUD dengan hubungan linear kuat (R² > 0,99). NTCP tertinggi ditemukan pada lensa mata (78,77%), parotis (73,81%), dan koklea (59,04%) dengan koklea melampaui ambang klinis pada pergeseran maksimum. Pergeseran sumbu-Y memberikan dampak lebih besar dibandingkan sumbu-X pada seluruh parameter, sehingga verifikasi posisi pasien yang ketat terutama pada arah longitudinal sangat diperlukan dalam radioterapi kanker nasofaring.
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Nasopharyngeal cancer is one of the most commonly treated cancers using radiotherapy, particularly with the volumetric-modulated arc therapy (VMAT) technique, which provides precise dose distribution. However, isocenter shifts due to patient positioning uncertainties may affect dose accuracy and radiobiological response. This study aimed to analyze the effect of patient positioning shifts at the isocenter on dosimetric and radiobiological parameters in VMAT-based nasopharyngeal cancer radiotherapy. This study employed a simulation-based approach using the treatment planning system (TPS) with secondary data from 10 patients, simulating isocenter shifts of ±1, ±2, and ±3 mm along the X-axis (lateral) and Y-axis (longitudinal), generating 130 datasets. The evaluated parameters included the dose distribution on the PTV and OAR, as well as the HI, CI, TCP, and NTCP. The results showed that D2% did not produce hotspots under any shift condition (p > 0.05), whereas D98% decreased significantly (p = 0.005), causing underdose below 95% of the prescribed dose, particularly at ±3 mm shifts. The HI increased up to 0.18 and the CI decreased to 0.85, with the greatest degradation observed along the Y-axis. The TCP decreased proportionally with the EUD reduction, showing a strong linear relationship (R² > 0.99). The highest NTCP values were found in the lens (78.77%), parotid (73.81%), and cochlea (59.04%), with the cochlea exceeding the clinical threshold at maximum shift. Y-axis shifts demonstrated a greater impact than X-axis shifts across all parameters, emphasizing the critical importance of strict patient positioning verification, particularly in the longitudinal direction, in nasopharyngeal cancer radiotherapy.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	Isocenter, Kanker nasofaring, Kesalahan posisi pasien, Radiobiologi, Radioterapi, Isocenter, Nasopharyngeal cancer, Patient set-up error, Radiobiology, Radiotherapy
Subjects:	Q Science > QC Physics > QC795.5 Radioactivity and radioactive Instruments and apparatus (General)
Divisions:	Faculty of Science and Data Analytics (SCIENTICS) > Physics > 45201-(S1) Undergraduate Thesis
Depositing User:	Yessa Gresianatasa Zahara
Date Deposited:	28 Jul 2026 02:06
Last Modified:	28 Jul 2026 02:06
URI:	http://repository.its.ac.id/id/eprint/138293

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