Bondel Shwetha, Ravikumar Manickham, Supe Sanjay Sudhakar, Reddy Buchuppudi Rekha
Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bangalore 560 029, India.
Rep Pract Oncol Radiother. 2013 Aug 23;19(3):151-6. doi: 10.1016/j.rpor.2013.07.014. eCollection 2014 May.
To calibrate Ir-192 high dose rate (HDR) brachytherapy source using different calibration methods and to determine the accuracy and suitability of each method for routine calibrations.
The source calibration is an essential part of the quality assurance programme for dosimetry of brachytherapy sources. The clinical use of brachytherapy source requires an independent measurement of the air kerma strength according to the recommendations of medical physics societies.
The Ir-192 HDR brachytherapy source from Gammamed plus machine (Varian Medical Systems, Palo Alto, CA) was calibrated using three different procedures, one using the well-type ionization chamber, second by the in-air calibration method and third using solid water phantoms. The reference air kerma rate (RAKR) of the source was determined using Deutsche Gesellschaft fur Medizinische Physik (DGMP) recommendations.
The RAKR determined using different calibration methods are in good agreement with the manufacturer stated value. The mean percentage variations of 0.21, -0.94, -0.62 and 0.58 in RAKR values with respect to the manufacturer quoted values were observed with the well-type chamber, in-air calibration, cylindrical phantom and slab phantom measurements, respectively.
Measurements with a well-type chamber are relatively simple to perform. For in-air measurements, the indigenously designed calibration jig provides an accurate positioning of the source and chamber with minimum scatter contribution. The slab phantom system has an advantage that no additional phantom and chamber are required other than those used for external beam therapy dosimetry. All the methods of calibration discussed in this study are effective to be used for routine calibration purposes.
使用不同校准方法对铱-192高剂量率（HDR）近距离治疗源进行校准，并确定每种方法用于常规校准的准确性和适用性。
源校准是近距离治疗源剂量测定质量保证计划的重要组成部分。近距离治疗源的临床使用需要根据医学物理学会的建议独立测量空气比释动能强度。
使用三种不同程序对来自伽马刀plus机器（瓦里安医疗系统公司，加利福尼亚州帕洛阿尔托）的铱-192 HDR近距离治疗源进行校准，一种使用井型电离室，第二种采用空气中校准方法，第三种使用固体水模体。使用德国医学物理学会（DGMP）的建议确定源的参考空气比释动能率（RAKR）。
使用不同校准方法确定的RAKR与制造商规定值高度一致。分别通过井型电离室、空气中校准、圆柱形模体和平板模体测量观察到，相对于制造商引用值，RAKR值的平均百分比变化分别为0.21、-0.94、-0.62和0.58。
使用井型电离室进行测量相对简单。对于空气中测量，本土设计的校准夹具能以最小散射贡献实现源和电离室的精确定位。平板模体系统的优势在于，除了用于外照射治疗剂量测定的模体和电离室外，无需额外的模体和电离室。本研究中讨论的所有校准方法均可有效用于常规校准目的。
