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Abstrak :
[ABSTRAK
Dosimetri CT scan dapat dilakukan dengan menggunakan konsep CTDI, Monte Carlo, atau dengan pengukuran langsung dalam fantom fisis. Pengukuran langsung menggunakan thermoluminescent dosimeter (TLD) merupakan prosedur yang rumit dan membutuhkan waktu yang lama. Saat ini sudah tersedia film radiochromic yang dapat digunakan di radiologi. Pada penelitian ini dilakukan pengukuran distribusi dosis radiasi dalam fantom Rando menggunakan film Gafchromic XR-QA2 dan TLD. Film Gafchromic XR-QA2 dan TLD dikalibrasi di CT scanner Siemens Sensation 64. Pengukuran distribusi dosis dengan film dilakukan pada faktor pitch 0.8, 1.0, dan 1.4. Film Gafchromic XR-QA2 disisipkan diantara slab 22-23 (Film A), 23-24 (Film B), dan slab 24-25 (Film C). Pengukuran distribusi dosis dengan TLD dilakukan dalam slab nomor 23 dengan faktor pitch 1.4. Film Gafchromic XR-QA2 yang telah dieksposi dipindai dengan flatbed scanner Epson Perfection V700 Photo. Dosis serap tulang belakang pada Film A, Film B, dan Film C yang dieksposi dengan faktor pitch 1.4 secara berturut-turut adalah 2.0 mGy, 1.9 mGy, dan 2.2 mGy. Berdasarkan profil dosis, rata-rata dosis serap pada film yang dieksposi dengan faktor pitch 1.0 dan 1.4 secara berturut-turut adalah 8% dan 24% lebih tinggi dibanding rata-rata dosis serap pada film yang dieksposi dengan faktor pitch 0.8. Rentang dosis hasil pengukuran dengan TLD adalah (1.9 ± 0.1) – (2.3 ± 0.2) mGy dan rentang dosis hasil pengukuran dengan film Gafchromic XR-QA2 adalah 1.8 – 2.3 mGy dengan perbedaan maksimum 10.6%. Perbedaan tersebut masih berada dalam rentang keakurasian TLD yaitu < 15%. Berdasarkan hasil tersebut, film Gafchromic XRQA2 dapat digunakan untuk pengukuran dosis CT scan selanjutnya.

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ABSTRACT
Computed tomography (CT) dosimetry can be approached by using CTDI method, Monte Carlo computer technique, and direct measurement within physical phantom. Direct measurement using thermoluminescent dosimeters (TLDs) is a laborious procedure. Radiochromic film for radiology application was available. In this study, dose distribution within adult anthropomorphic physical phantom was measured using TLD and Gafchromic XR-QA2 film. TLD and Gafchromic XR-QA2 film was calibrated on CT scanner Siemens Sensation 64. Gafchromic XR-QA2 film was sandwiched between slab Rando phantom number 22-23 (Film A), 23-24 (Film B), and 24-25 (Film C). Pitch factor 0.8, 1.0, and 1.4 were used. TLDs were placed at the holes in the slab number 23 of anthropomorphic phantom. TLDs were scanned using pitch factor 1.4. After exposure, Gafchromic XR-QA2 film was digitized using Epson Perfection V700 Photo flatbed scanner. Absorbed dose at vertebra on Film A, Film B, and Film C which exposed by using pitch 1.4 respectively were 2.0 mGy, 1.9 mGy, and 2.2 mGy. Based on dose profile, average dose of XR-QA2 film which exposed by using pitch 1.0 and 1.4 respectively were 8% and 24% higher than average dose of XR-QA2 film which exposed by pitch 0.8. TLDs dose range were (1.9 ± 0.1) – (2.3 ± 0.2) mGy and Gafchromic XR-QA2 film dose range were 1.8 – 2.3 mGy with maximum difference 10.6%. The difference is still within the range of TLD accuracy, < 15%. Based on this result, Gafchromic XR-QA2 film can be used to measure CT dose, Computed tomography (CT) dosimetry can be approached by using CTDI method, Monte Carlo computer technique, and direct measurement within physical phantom. Direct measurement using thermoluminescent dosimeters (TLDs) is a laborious procedure. Radiochromic film for radiology application was available. In this study, dose distribution within adult anthropomorphic physical phantom was measured using TLD and Gafchromic XR-QA2 film. TLD and Gafchromic XR-QA2 film was calibrated on CT scanner Siemens Sensation 64. Gafchromic XR-QA2 film was sandwiched between slab Rando phantom number 22-23 (Film A), 23-24 (Film B), and 24-25 (Film C). Pitch factor 0.8, 1.0, and 1.4 were used. TLDs were placed at the holes in the slab number 23 of anthropomorphic phantom. TLDs were scanned using pitch factor 1.4. After exposure, Gafchromic XR-QA2 film was digitized using Epson Perfection V700 Photo flatbed scanner. Absorbed dose at vertebra on Film A, Film B, and Film C which exposed by using pitch 1.4 respectively were 2.0 mGy, 1.9 mGy, and 2.2 mGy. Based on dose profile, average dose of XR-QA2 film which exposed by using pitch 1.0 and 1.4 respectively were 8% and 24% higher than average dose of XR-QA2 film which exposed by pitch 0.8. TLDs dose range were (1.9 ± 0.1) – (2.3 ± 0.2) mGy and Gafchromic XR-QA2 film dose range were 1.8 – 2.3 mGy with maximum difference 10.6%. The difference is still within the range of TLD accuracy, < 15%. Based on this result, Gafchromic XR-QA2 film can be used to measure CT dose]

Abstrak :
ABSTRAK
Potensi induksi radiasi sekunder tidak hanya bergantung pada jumlah dosis penyerapan yang diberikan, tetapi juga pada karakteristik pasien. Selama perlakuan terapi menggunakan Gamma Knife Radiosurgery (GKRS), tubuh pasien menerima iradiasi akumulasi dosis hamburan dan kebocoran. Oleh karena itu, perlu untuk mengetahui dosis radiasi organ kritis pasien yang diterima selama perawatan Gamma Knife Radiosurgery dan membandingkan dengan batasan dosis masing-masing organ. Pengukuran dilakukan dengan menggunakan dosimeter film GafChromic XR-QA2 dan thermoluminescent dosimeter (TLD) yang diletakkan pada permukaan organ kritis fantom. Pemasangan head frame di fantom antropomorfik (Alderson Rando Phantom, Laboratorium Penelitian Alderson, Inc., Stamford, Connecticut) dan scalp measurement digunakan untuk mengukur geometri kepala fantom. Magnetic Resonance Imaging (MRI) digunakan untuk memperoleh citra fantom antropomorfik dan kemudian dipindahkan ke Leksell Gamma Planning (LGP) untuk menentukan perencanaan posisi target, distribusi dosis dan dosis preskripsi maksimum pada target 36 Gy. Unit LGK Perfexion (Elekta AB, Stockholm, Swedia) digunakan untuk menyinari fantom dengan target diposisikan di tengah, dan volume target divariasi dari 5 cc, 10 cc, 15, dan 20 cc serta ukuran kolimator dari 4 mm, 8 mm, dan 16 mm. Dosimeter diletakkan di permukaan lensa, tiroid, payudara, fundus uterus, ovarium, dan testis. Kemudian dosimeter dianalisa untuk memperoleh dosis pada organ kritis. Hasil pengukuran menunjukkan bahwa dosis yang terlihat pada lensa, tiroid, dan payudara dipengaruhi oleh jarak organ dari target, volume target, dan ukuran kolimator. Diperoleh bahwa dosis radiasi pada organ kritis berkontribusi kurang dari 3%, relatif terhadap dosis target maksimum. Dosis radiasi pada organ kritis yang diambil menggunakan film GafChromic XR-QA2 lebih tinggi dibandingkan TLD dengan diskrepansi mencapai 50%. Jika dibandingkan dengan referensi, pengukuran dosis XR-QA2 tidak jauh berbeda sehingga diketahui bahwa film XR-QA2 dapat digunakan untuk mengukur radiasi hambur. Namun, perhatian khusus dan optimisasi harus dilakukan untuk perencanaan perlakuan dengan mempertimbangkan ukuran kolimator yang digunakan dan meminimalkan waktu perlakuan.

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ABSTRACT
The potential for secondary radiation induction depends not only on the amount of absorption dose received, but also on patient characteristics, such as age (in general, younger patients will be more vulnerable). During treatment using Gamma Knife Radiosurgery (GKRS), patient's body receives an dose accumulation from scattering and leakage. Therefore, it is necessary to know the dose of patient's organs at risk (OAR) received during Gamma Knife Radiosurgery treatment and compare it with the dose limit of each organs. Measurements obtained using a GafChromic XR-QA2 dosimeter and thermoluminescent dosimeter (TLD) placed on the surface of phantom critical organs. Installation of head frame in anthropomorphic phantom (Alderson Rando Phantom, Alderson Research Laboratory, Inc., Stamford, Connecticut) and scalp measurement used to measure phantom head geometry. Magnetic Resonance Imaging (MRI) used to obtain anthropomorphic phantom image and then transferred to the Leksell Gamma Planning (LGP) to determine the planning treatment planning such as target position, dose distribution and target maximum prescription dose at 36 Gy. The LGK Perfexion unit (Elekta AB, Stockholm, Sweden) used to illuminate the phantom with the target positioned in the middle, and the target volume varies from 5 cc, 10 cc, 15 and 20 cc and collimator sizes from 4 mm, 8 mm and 16 mm. The dosimeters placed on the surface of the lens, thyroid, breast, uterine fundus, ovaries and testes. Then the dosimeters analyzed to obtain the dose in OAR. The measurement results shows that the dose at lens, thyroid, and breast depend on the distance from the target, target volume, and collimator size. The radiation dose in OAR contributed less than 3%, relative to the maximum target dose. The radiation dose in critical organs taken using GafChromic XR-QA2 film is higher than TLD with a 50% discrepancy. When compared with the reference, the measurement of XR-QA2 dose is not much different so it is known that XR-QA2 film can be used to measure scattering radiation. However, special attention and optimization must be done for treatment planning by considering the size of the collimator used and minimizing the treatment time.

Abstrak :
Computed Tomography (CT) merupakan modalitas sinar-X untuk membuat citra organ dalam tiga dimensi. Akuisisi citra dilakukan dengan perputaran tabung sinar-X yang disertai gerakan meja, sehingga tabung mengelilingi pasien dalam bentuk spiral. Gerakan meja pasien persatu rotasi gantry dibagi lebar kolimator pada isocenter dikenal dengan pitch, yang berpengaruh pada kualitas citra maupun dosis radiasi pada pasien. Telah diobservasi profil ditribusi dosis sepanjang sumbu-Z fantom simulasi toraks in house berbentuk silinder elips dengan ukuran 28 cm × 21 cm dan panjang 22 cm. Fantom terbuat dari bahan PMMA dengan Hounsfield Unit (123,10 ± 3,96 HU) dilengkapi dengan objek simulasi paru dari gabus patah (-790,60 ± 15,55 HU), dan tulang belakang dari material teflon dengan (918,60 ± 7,35) balok dan silinder untuk tempat film gafchromic ukuran 1 cm x 25 cm. Posisi film ditandai dengan 1-9 dengan koordinat berturut turut (0, 0), (5, 0), (10, 0), (-5, 0), (-10, 0), (0, 4), (0, 8), (0,-4), (0,-8). Citra fantom diakuisisi dengan kondisi eksposi 120 kV,100 mAs dan pitch 0,8, 1,0, dan 1,5. Dosis minimum terjadi pada awal dan akhir scan untuk seluruh profil dan nilai pitch, dosis rata-rata material paru (2, 3, 4, dan 5) dalam rentang (2,49-2,90) mGy untuk pitch 0,8 dan (2,36-2,88) mGy untuk pitch 1,0, serta (2,33-2,74) mGy untuk pitch 1,5, relatif lebih rendah disbanding dengan pada jaringan lunak dan tulang. Dosis maksimum selalu terjadi di pertengahan sumbu-Z. Dapat disimpulkan bahwa penggunaan pitch 0,8 dan 1,0 tidak memberikan perbedaan dosis yang signifikan dan menurunkan dosis rata-rata pada pitch 1,5. Selain itu dosis maksimum tidak selalu terjadi di pertengahan sumb-z dikarenakan oleh material isotropis.

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Computed Tomography (CT) is an X-ray modality for scanning organ in three dimensional images. Image acquisition is performed by rotating X-ray tube that match with table movements, there by the tube can cover patient body in a spiral scan. Patient table movements by gantry rotation divided by the width of the collimator on the isocenter is known as a pitch, which affects the image quality and radiation dose in the patient. A dose distribution profile has been observed along the z-axis of the in-house thorax phantom simulation in an elliptical cylinder form with the size of 28 cm x 21 cm and 22 cm length. Phantom is made from PMMA with Hounsfield Unit (123.10 ± 3.96 HU) was equipped with a lungs simulation object using a cork (-790.60 ± 15.55 HU), a spine using Teflon material (918.6 ± 7.35 HU), and 9 bar and a cylinder to place 1 cm x 25 cm gafchromic films. The position of the film was marked with point position 1-9 for the series of coordinates (0,0), (5, 0), (10, 0), (-5, 0), (-10, 0), (0, 4), (0, 8), (0,-4), (0, -8) cm. The phantom images was performed with an exposure condition by 120 kV, 100 mAs and pitch variations (0.8, 1.0 and 1.5). The minimum dose occured at the beginning and end of the scan for all profiles and pitch values. The average dose of lung material (2, 3, 4, and 5) in the range (2.49-2.90) mGy for pitch 0.8, (2.36-2.88) mGy for pitch 1.0 and (2.33-2.74) mGy for pitch 1.5. The dose in lung was relatively lower compared to the dose in soft tissue and bone. The maximum dose always occur in the middle of the z-axis. It can be concluded that the use of pitch 0.8 and 1.0 did not provide a significant dose difference and reduced the average dose on pitch 1.5. Moreover, the maximum dose does not always occur in the middle of the z-axis due to an isotropic material.

Abstrak :
Teknik akuisisi scan spiral memperkenalkan istilah Pitch. Pitch yang besar mempengaruhi proses rekonstruksi karena interpolasi data menjadi lebih lebar sehingga dapat menurunkan resolusi citra. Penelitian ini dilakukan dengan menggunakan fantom toraks in house yang dibuat dan didesain berdasarkan pengukuran data citra CT Toraks 100 pasien laki-laki. Parameter eksposi yang digunakan 130 kVp, rotasi tabung 0,6 detik, perubahan arus tabung 70 mAs dan 100 mAs serta variasi pitch mulai dari 0.5, 0.8, 1, 1.5, 1.8 dan 2. Fantom terbagi menjadi 4 bagian. Fantom bagian A untuk evaluasi akurasi posisi dan kualitas citra pada selang berisi media kontras, bagian B untuk evaluasi kualitas citra lubang udara hole , bagian C untuk evaluasi mikrokalsifikasi dengan variasi ukuran mesh pada serbuk tulang dan hidroxyapatite, dan bagian D untuk evaluasi MTF. Scanning fantom A untuk evaluasi akurasi posisi selang antara ukuran di fantom dengan monitor menunjukkan deviasi < 4 berjumlah 408 data 84 di sisi kanan dan 417 data 86 di sisi kiri dari total 486 data. Evalusi kualitas citra pada fantom A, terdapat perbedaan ?SNR pada tiap slice dengan hubungan yang linier terhadap perubahan pitch, semakin besar pitch yang digunakan ?SNR akan semakin lebar. ?SNR paling lebar terdapat pada slice ke-1 dan ke-2, selanjutnya pada slice ke-3 sampai ke-9 ?SNR stabil dan cenderung menurun. Evaluasi fantom B menunjukkan hole titik I dan J yang berdiameter 0.9 mm dan 0.625 mm tidak dapat tervisualisasi pada seluruh slice. SNR yang didapat paling tinggi pada hole tengah titik H dengan diameter 2 mm. Sensitivitas Pesawat CT dapat mendeteksi serbuk tulang ukuran mesh 10 dan 30 tetapi tidak dapat memperlihatkan serbuk tulang ukuran mesh 50 yang tersebar merata di permukaan fantom, ditunjukkan dengan nilai SNR tertinggi pada pitch 0.8 sebesar 2.659 SNR. ......Acquisition technique in spiral scan introduce the term of Pitch. The big pitch could be influence for reconstruction process because interpolation will be wider, be affecting the spatial resolution. This study was performed by using in house thoracic phantom that made and designed based on image data measurement of CT Thorax of 100 men patient. Exposure Parameter which used was 130 kVp, tube rotation 0.6 second, tube current 70 mAs and 100 mAs, with pitch variation start from 0.5, 0.8, 1, 1.5, 1.8 and 2. Phantom was divided into 4 parts. Part A was used for evaluating the accuracy of position and image quality on a pipe that consist of contrast media, part B was used for evaluating image quality on hole, part C was used for evaluating micro calcification with various mesh size on bone material and hidroxyapatite, while part D was used for evaluating MTF. Phantom A scanning was performed for evaluating the accuracy of position between pipe in phantom and monitor showed deviation 4 with 408 number of data 84 on the right side and 417 data 86 on the left side from 486 all data. The result obtained for image evaluation, showed the different between delta SNR in every slice in phantom A with the pitch changing, used higher pitch becoming SNR wider. The widest SNR were occurred in the 1st and 2nd slice, furthermore in the 3rd until 9th slice SNR were stable and tend to decreased. Evaluation of phantom B showed that hole in point I and J which have diameter 0.9 mm and 0.625 mm could not visualized. The highest SNR was occurred in the middle hole point H with diameter 2 mm. The sensitivity of CT scanner is good enough to detect bone with the mesh size of 10 and 30 but not with the mesh size of 50 that spread in the phantom surface, this is shown with the highest SNR in the pitch 0.8 as 2.659 SNR.