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"ABSTRAKFilm EBT3 merupakan model film radiochromic yang didisain khusus untuk keperluan radioterapi eksternal (external beam therapy, EBT) respon film terhadap radiasi pengion mengakibatkan perubahan pada spektrum serapan dan sifat optiknya membuat film radiochromic menjadi pilihan yang banyak digunakan dalam bidang oncologi. Responfilm terhadap radiasi biasanya diukur dalam hal perubahan kerapatan optik (netOD) yang nilainya bergantung dari banyaknya berkas yang melewati film dan juga panjang gelombang cahaya dari alat pembaca (densitometer optik). Penelitian ini bertujuan menyelidiki pengaruh penggunaan densitometer optik yang berbeda, yakni scanner, densitometer dan spektrofotometer dalam mengukur respon dosimeter film terhadap radiasi pengion. Penyelidikan respon film dilakukan dengan mengirradiasi film menggunakan pesawat Linac Varian Trilogy dengan energi 6 MV. netOD yang terbaca pada film dilakukan dengan mengekstrak mean pixel value dari kanal merah ketika menggunakan scanner. Ketika menggunakan densitometer netOD dihasilkan dariperubahan nilai OD yang terbaca secara langsung. Sedangkan nilai netOD didapat dengan melihat perubahan spektrum serapan film sesudah dan sebelum irradiasi menggunakan spektrofotometer. Evaluasi penggunaan metode dosimetri dilakukan menggunakanfantom homogen untuk evaluasi dosis uji dan juga untuk evaluasi pada variasi lapangan penyinaran, dan fantom non-homogen (rando) untuk implementasi metode pada perlakuan klinis radioterapi. Untuk mendapatkan hasil pengukuran yang optimum juga dilakukan penyelidikan karakteristik spektrum serapan pada variasi level dosis dan variasi waktu pengukuran pasca irradiasi. Hasil pengukuran respon film menunjukkan tidak terjadi perubahan pita serapan film terhadap perubahan level dosis ataupun terhadap perubahan waktu pasca irradiasi, yakni berada pada pusat pada panjang gelombang 635nm untuk pita serapan maksimum, dan pita serapan ke-dua berpusat pada 583 nm. Penyelidikan sensitivitas ketiga metode menghasilkan tren kurva sensitivitas yang mirip namum memiliki besar yang berbeda dimana sensitivitas tertinggi didapat ketika menggunakan spektrofotometer. Sementara ketidakpastian (1σ) netOD untuk ketigametode menghasilkan nilai ketidakpastian yang cukup besar untuk dosis dibawah 100 cGy dan nilai ketidakpastian mulai membaik ketika level dosis meningkat. Pada aplikasi klinis ketiga metode dosimeteri dievaluasi dengan melihat besar diskrepansi yang dihasilkan pada adaerah target kepala, paru-paru dan prostat. Penggunaan scanner danspektrofotometer menghasilkan rata-rata diskrepansi dibawah 2% untuk semua target pengukuran, sedangkan densitometer menghasilkan rata-rata diskrepansi sampai 3%.

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ABSTRACTEBT3 film is a radiochromic film model specially designed for external radiotherapy (EBT). The response of the film to ionizing radiation results in changes in the absorption spectrum and its optical properties making radiochromic films a widely used choice in oncology. The response of the film to radiation is usually measured in terms of the change in optical density (netOD) whose value depends on the number of beams passing through the film and also the wavelength of light from the reader (optical densitometer). This study aims to investigate the effect of using different optical densitometers, namely scanners, densitometers and spectrophotometers in measuring the response of film dosimeters to ionizing radiation. The investigation of the film response was carried out by irradiating the film using a Linac Varian Trilogy with an energy of 6 MV. The netOD read on the film was done by extracting the mean pixel value from the red channel when using a scanner. When using a densitometer the netOD results from changes in OD values that are read directly. While the netOD value was obtained by measuring changes in the absorption spectrum of the film after and before irradiation using a spectrophotometer. Evaluate the use of the dosimetric methods was carried out using homogeneous phantomfor the evaluation of test doses and also for evaluation of variations in the radiation field, and non-homogeneous phantom (rando) for the implementation of the method in clinical radiotherapy treatment. To obtain the optimum measurement results, an investigation of the characteristics of the absorption spectrum was also carried out at variations in dose levels and variations in measurement time after irradiation. The results of the measurement of the response of the film showed that there was no change in the absorption band of the film due to changes in dose levels or to changes in time after; irradiation, which was at the center at a wavelength of 635 nm for the maximumabsorption band, and the second absorption band was centered at 583 nm. The sensitivityinvestigation of the three methods resulted in a trend of similar sensitivity curves but different magnitudes with the highest sensitivity obtained when using a spectrophotometer. Meanwhile, the uncertainty (1σ) netOD for the three methods resultedin a fairly large uncertainty value for doses below 100 cGy and the uncertainty value began to decrease as the dose level increased. In clinical application, the three dosimetric methods were evaluated by measuring the resulting discrepancy in the target areas of thehead, lungs and prostate. The use of a scanner and a spectrophotometer resulted in an average discrepancy of below 2% for all measurement targets, while the use of a densitometer resulted in an average discrepancy of up to 3%."

"[ABSTRAKFilm gafchromic EBT2 dan EBT3 cocok digunakan untuk jaminan kualitas (QA) pada treatment planning systems (TPS) dan linear accelerator (LINAC) serta verifikasi radioterapi teknik IMRT dan VMAT. Namun generasi selanjutnya dari film gafchromic EBT yaitu EBT2 dan EBT3 ketika dilakukan scanning (pemindaian) menggunakan scanner flatbed masih terdapat artefak geometris yang dahulunya juga ditemukan pada film EBT sehingga memerlukan penanggulangan dan koreksi yang sesuai. Pada penelitian ini menggunakan scanner flatbed Epson expression 10000XL, Epson perfection V700 dan Mikrotek 1000XL plus yang dapat menangkap warna dengan rinci dan presisi. Perangkat lunak yang digunakan dalam koreksi ini adalah FilmQA Pro 2015. Hasil yang diperoleh yaitu Koefisien A dan B diterapkan untuk variasi posisi lateral terhadap nilai tanggapan di lokasi yang bersamaan, sehingga pengkoreksian tanggapan artifak lateral dapat dilakukan. Pada dosis maksimum nilai koreksinya <0,5% dan pada kasus <0.2%. Pada pengukuran ulang untuk setiap film, standar deviasi yang diperoleh untuk setiap film sekitar 0.19%. Pengujian dosimetri channel tunggal (merah) sebelum dan sesudah koreksi pada kasus IMRT didapatkan hampir 91% dari piksel memenuhi 3% / 3mm kriteria gamma keseluruhan dengan ambang batas dosis > 10%. Untuk pengujian kasus VMAT, film di scan dengan posisi di pusat scanner dan posisi ektrim tepi scanner, maka pengukuran di channel warna merah 4% lebih tinggi dibandingkan channel warna hijau dan biru. Rata-rata konsistensi pengukuran dosis selama daerah terkena dosis > 100 cGy adalah sekitar 21,8 cGy dan di daerah yang paling dekat dengan tepi scan window sekitar 10 mm dengan perbedaan dosis 35 cGy. Setelah dilakukan koreksi, rata-rata konsistensi dosis pada tiga channel di sekitar daerah terpapar sekitar 5,1 cGy. Perbedaan dosis antar channel sekitar 9 cGy. Hasil ini menunjukkan koreksi respon artefak lateral memang perlu dilakukan. Respon yang diukur tergantung pada posisi film pada pemindai dan dosis yang diberikan. Pengukuran pada channel warna merah menunjukkan sensitivitas yang lebih besar pada dosis rendah, sedangkan respon pada channel hijau atau biru memberikan perpanjangan jangkauan dinamis dari film ke dosis tinggi. Metode triple-channel dosimetri telah terbukti memiliki keuntungan signifikan atas single channel dosimetry dengan akurasi dosimetri yang baik.

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ABSTRACT

The film of gafchromic EBT2 and EBT3 are appropriate for quality assurance (QA) to the radiotherapy technics verification of IMRT and VMAT. In the next generations of EBT which are EBT2 and EBT3, are still attained the geometrical artifacts once scanning by flatbed scanner which is used to be found on EBT film in order to need an overcome ways and an appropriate correction. This research used a flatbed scanner EPSON expression 10000XL, EPSON perfection V700 and Microtech 1000XL plus and FilmQA Pro 2015 as a software for correcting it. The result shows that coefficient A and B were applied for lateral correction artifacts responses can be made. On the maximum dose, it has correction value as much as <0,5% and in case was <0.2%. The deviation standard was approximately 0,19% on re-measure for each film. Prior to the dosimetry measurement of single channel (red) and subsequent to the correction IMRT has got almost 91% of pixel which met with gamma criteria, 3% / 3mm, with dose threshold 10% TH. In the measurement of VMAT‟s case, film scanned on the center of scanner and the extreme position of the scanner edge. Thus, measurement in the red channel was 4% higher than green and blue channel. The average of dose measurement consistency during area exposed to doses > 100 cGy is approximately 21,8 cGy and the closest area with the edge of scan window is around 10 mm at difference doses 35 cGy. After correction, the average of doses consistency was 5,1 cGy on the three channel where exposed. The distinction of doses was approximately 9 cGy among channels. This result stated that the correction of artifacts lateral response is needed to carry on. The method of triple-channel dosimetry has the significant advantage on single-channel dosimetry with a good consistency. Through escalation dose and variation of lateral position, the distinct response would be increased on single-channel which is red channel. The measurement on red channel reveals the highest sensitivity on the slight dose. Whereas, a green or blue channel response provides a dynamic range extension of film to a high dose. Thus, the method of dosimetry triple-channel has the significant contribution of single-channel evidently with a good dosimetric accuracy., The film of gafchromic EBT2 and EBT3 are appropriate for quality assurance (QA) to the radiotherapy technics verification of IMRT and VMAT. In the next generations of EBT which are EBT2 and EBT3, are still attained the geometrical artifacts once scanning by flatbed scanner which is used to be found on EBT film in order to need an overcome ways and an appropriate correction. This research used a flatbed scanner EPSON expression 10000XL, EPSON perfection V700 and Microtech 1000XL plus and FilmQA Pro 2015 as a software for correcting it. The result shows that coefficient A and B were applied for lateral correction artifacts responses can be made. On the maximum dose, it has correction value as much as <0,5% and in case was <0.2%. The deviation standard was approximately 0,19% on re-measure for each film. Prior to the dosimetry measurement of single channel (red) and subsequent to the correction IMRT has got almost 91% of pixel which met with gamma criteria, 3% / 3mm, with dose threshold 10% TH. In the measurement of VMAT‟s case, film scanned on the center of scanner and the extreme position of the scanner edge. Thus, measurement in the red channel was 4% higher than green and blue channel. The average of dose measurement consistency during area exposed to doses > 100 cGy is approximately 21,8 cGy and the closest area with the edge of scan window is around 10 mm at difference doses 35 cGy. After correction, the average of doses consistency was 5,1 cGy on the three channel where exposed. The distinction of doses was approximately 9 cGy among channels. This result stated that the correction of artifacts lateral response is needed to carry on. The method of triple-channel dosimetry has the significant advantage on single-channel dosimetry with a good consistency. Through escalation dose and variation of lateral position, the distinct response would be increased on single-channel which is red channel. The measurement on red channel reveals the highest sensitivity on the slight dose. Whereas, a green or blue channel response provides a dynamic range extension of film to a high dose. Thus, the method of dosimetry triple-channel has the significant contribution of single-channel evidently with a good dosimetric accuracy.]"