J URNAL FISIKA DAN APLIKASINYA VOLUME 16, NUMBER 2, J UNE 2020 Evaluation of Well-Type Chamber Calibration Factor for Measurement of Ir-192 Brachytherapy Source Over 10 Institutions Assef Firnando Firmansyah, Okky Agassy Firmansyah, Sri Inang Sunaryati, and Nurman Rajagukguk Center for Technology of Safety and Radiation Metrology (PTKMR) BATAN Jl. Lebak Bulus Raya, Jakarta Selatan, 12440 Abstract: This paper describes the evaluation of well-type chamber calibration factor for measurement Ir- 192 brachytherapy source. Data were collected at ten institutions of Ir-192 brachytherapy facilities. Calibration was carried out using the substitution method adopted from a protocol published by the International Atomic Energy Agency. The well-type chamber standard used was HDR-1000 Plus. The results obtained that NAKS for well-type chamber from PTW manufacturers has a range of values from 9.063 × 10 5 -9.875 × 10 5 Gy m 2 h -1 A -1 with an average value 9.522 × 10 5 Gy m 2 h -1 A -1 , while the well-type chamber from Standard Imaging manufacturers has a range of values from 4.634 × 10 5 -4.662 × 10 5 Gy m 2 h -1 A -1 with an average value 4.648 × 10 5 Gy m 2 h -1 A -1 . The range of deviations obtained between NAKS-new and N AKS-old ranges from 0.8% to -1.8%, while the range of normalization results of NAKS-new to the average value of NAKS-new ranges from 0.952-1.029. There was one calibration factor that has a deviation of more than 1% over the N AKS-old . Based on the calculation of uncertainty, all the calibration factor results obtained were still within the accepted range. Keywords: air Kerma strength; brachytherapy; calibration factor; well-type chamber. *Corresponding author: oafirmansyah@gmail.com http://dx.doi.org/10.12962/j24604682.v16i2.6406 2460-4682 c Departemen Fisika, FSAD-ITS I. INTRODUCTION The use of brachytherapy modalities for cancer treatment has been used for more than 120 years in the world [1]. His- tory records that the first clinical case handled by brachyther- apy is a case with gynecologic cancer patients [2]. The devel- opment of brachytherapy initially used a radium source, then developed in the presence of artificial radiation sources such as Co-60, Cs-137, and Ir-192 [3]. In Indonesia, the use of brachytherapy modalities for can- cer treatment has also developed quite rapidly. Some research references regarding the modality of brachytherapy have also been carried out by Indonesian researchers [4][7]. The most commonly used isotope as a radiation source was Ir-192, which has a half-life of 73,825 days with an average energy of 350 keV. In addition to Ir-192, some hospitals use Co-60 radiation sources, which have a half-life of 5.27 years with an average energy of 1250 keV [8]. There were several protocols in dosimetry for brachyther- apy that have been published such as those published by the International Atomic Energy Agency (IAEA) namely IAEA TEC-DOC No. 1079 which was later revised to IAEA TEC- DOC No. 1274, or AAPM TG-56 published by the Ameri- can Association of Physicists in Medicine (AAPM). Several methods were available for measuring brachytherapy sources, namely free in air measurement and measurements using a well-type ionization detector [9][12]. Free in air measure- ment, use a standard ionization chamber 0.6 cm3 with a seven-distance measurement method[13]. In several publica- tions, the well-type chamber was the recommended ioniza- tion chamber due to several advantages [10], [14], [15]. This well-type chamber can measure the source of brachytherapy in terms of air Kerma strength (AKS) [16]. Until the end of 2019, there were about fourteen hospi- tals using brachytherapy modalities to treat cancer. Ten of them use the Ir-192 source as a source of brachytherapy. The brachytherapy and dosimeter used were from several manu- facturers. The dosimeter used also has various calibration fac- tors and traceability from several calibration laboratories or from the manufacturer certificate. The use of brachytherapy modalities in Indonesia was regu- lated through the Head of Nuclear Energy Regulatory Agency of Indonesia (BAPETEN), which one of the rules requires the hospital to calibrate the radiation sources of the brachyther- apy and its dosimeters [17]. The purpose of this regulation was to guarantee the safety and health of ionizing radiation [18]. Based on these regulations, every hospital in 2019 was required to calibrate dosimeters for brachytherapy every year. The urgency of the calibration radiation measuring instrument calibration is to ensure the quality of service in accordance with established quality requirements. This paper discusses the evaluation of the value of the cali- bration factor in terms of the air Kerma strength (Gy m 2 h -1 A -1 ) from ten hospitals in Indonesia that use the modality of Ir-192 brachytherapy. The purpose of this study was to deter- mine the range of calibration factor values based on the brand