No abstract

A concept of radiation beam matching of some medical linear accelerators (LINACs) that have identical characteristics of the models, radiation quality, and multileaf collimator features may be implemented as long as the manufacturer provides complete specifications so that a Treatment Planning System (TPS) can be used for many beam-matched LINACs. This paper describes a preliminary study on the implementation of the beam matching concept for five units Elekta Precise Treatment System LINACs that have recently been installed in Indonesia. The beam matching criteria were based on the percentage depth dose (PDD) and beam profile for photon and electron beams. Dosimetry measurements were carried out by using an SNC 125 ionization chamber of 0.125 cm 3 in volume, PTW Pinpoint 3D of 0.016 cm 3 in volume, and PTW Farmer Chamber of 0.6 cm 3 in volume. The results indicated that the PDD 10 of 6 and 10 MV photon beams among installed five units LINACs have excellent compatibility each others with a maximum deviation of less than 0.4 %, while the maximum deviation for dose depth of 80 % (R 80 ) for the electron beams with nominal energies of 4, 6, 8, 10, 15 and 18 MeV is 1 mm. The measurement results for the flatness profile were less than 6 %, and symmetry profiles were less than 3 %. It also outlines the determination of the absorbed dose to water under reference conditions. The results of the calibration of output doses show that the absorbed dose in the water was 1 cGy ≈ 1 MU. The data obtained from measurements for each LINAC conform with the requirements of the beam matching process set by the manufacturer.

Gamma Knife Stereotactic Radiosurgery (GKSRS) treatment requires the high accuracy of delivering single high dose without negative impact on the surrounding tissue. During radiosurgery treatments using GKSRS, the surrounding tissue will receive high scatter radiation because the single dose treatment will employed long irradiation time. Therefore, radiation doses in critical organs of patients during GKSRS treatment is important to be evaluated. In this study, we investigated the radiation dose to the lens, thyroid, breast, uterine fundus, ovaries and testes during treatment using Leksell Gamma Knife Perfexion (LGK; Elekta AB, Stockholm, Sweden). The dose was simulated using the variation of tumour target from 5 to 20 cc. The measurement were performed using variation of collimator size of 4 mm, 8 mm, 16 mm and employed thermoluminescent dosimeters (TLDs) to be placed at the surface of Rando anthropomorphic phantom. TLDs reader Harshaw model 3500 were employed to evaluate the measurement result. The result of this study explains that the dose of organs at risk decrease linearly depend on the distance of the target, target volume and the size of collimator.

ANALISIS PENENTUAN PDD BERKAS FOTON 6 DAN 10 MV FREE FLATTENING FILTER (FFF) PADA LAPANGAN KECIL MENGGUNAKAN TIGA DETEKTOR YANG BERBEDA. Analisis penentuan persentase dosis kedalaman untuk berkas foton 6 dan 10 MV flattening filter free (FFF) pada lapangan kecil menggunakan variasi detektor. Makalah ini menguraikan penentuan persentase dosis kedalaman dari berkas foton 6 dan 10 MV FFF yang dipancarkan pesawat pemercepat linier medik Versa HD. Pengukuran dilakukan menggunakan 3 jenis detektor yaitu IBA Razor dioda, PTW PinPoint 3D dan IBA CC13 yang dihubungkan dengan elektrometer IBA Dose 1.  Pengukuran  dilakukan di dalam fantom air Blue Fantom IBA yang dilengkapi dengan perangkat lunak MyQA Accept pada jarak sumber radiasi ke permukaan 100 cm dengan variasi lapangan radiasi 1 x 1 cm2, 2 x 2 cm2, 3 x 3 cm2 dan 4 x 4 cm2. Berdasarkan data yang didapatkan deviasi pengukuran antara detektor IBA Razor terhadap detektor PinPoint 3D didapatkan rentang deviasi 1.8% - 2.1%. Berbeda dengan deviasi pengukuran antara detektor IBA CC13 terhadap dektektor PinPoint 3D yang mendapatkan rentang deviasi 0,15% - 0,21%. Maka dapat disimpulkan bahwa pengukuran menggunakan tiga tipe detektor ini menunjukkan adanya kesesuaian dengan deviasi terbesar lebih kecil dari 3,5%. Detektor PinPoint 3D, Detektor IBA Razor, dan IBA CC13 dapat digunakan untuk melakukan pengukuran relatif pada lapangan kecil hingga 1 x 1 cm2 pesawat pemercepat linier medik.

<p><em>The value of H_p(10) can be measured directly using H_p(10) secondary standard chamber that developed by Physikalisch Technische Bundensalt (PTB), Germany. H_p(10) secondary standard chamber type T 34035/0046 is connected with electrometer PTW Unidos T 10001 / Ns.11814. In this paper, the exposure was carried out by X-ray sources and ¹³⁷Cs for dose and radiation energy variations.The variations energy of X-ray were carried out using ISO 4037-1 quality narrow (N) spectrum within N-40 to N-300, while the radiation dose variations were carried out in the dose within range 0.1 mSv to 20 mSv. The use of the S-¹³⁷Cs calibration factor for the H_p(10) secondary standard chamber with an X-ray irradiation source were carried out and obtained a fairly good response result not in all energy ranges. The result obtained a relatively constant response to energy of 65 keV to 250 keV (energy quality N-80 to N-250), this corresponds to the deviation obtained i.e ≤ 7% from the normalization reference source of ¹³⁷Cs at 662 keV energy. Whereas for deviations below 3%, a relatively constant response has founded in the energy range of 100 keV to 250 keV (energy quality N-120 to N-250). The result obtained linier measurement on variations in dose according to changes in dose variation. The H_p(10) secondary standard chamber is capable for measuring variations of radiation dose, i.e from variations of 0.1 mSv to 20 mSv.</em></p>