Establishment of an absolute measurement of the reference air kerma rate for HDR 192Ir brachytherapy sources.

Purpose: Before this study, no institution in China had undertaken the calculation and official establishment of reference values for the reference air kerma rate associated with high-dose rate ¹⁹²Ir sources used in brachytherapy. This research, carried out at the National Institute of Metrology (NIM) in China, has successfully established an ¹⁹²Ir reference radiation facility. Consequently, it has achieved the absolute measurement of the reference air kerma rate for high-dose rate brachytherapy using ¹⁹²Ir sources.

Methods and materials: For this study, a medical afterloader machine was acquired. The radiation source employed was a high-dose rate ¹⁹²Ir source for brachytherapy, produced by HTA Co., Ltd. A reference graphite cavity ionization chamber with a volume of 100 cm³ was designed to serve as the ionization chamber for absolute measurements. The determination of various correction factors and physical constants was achieved through a method that combines Monte Carlo simulations with experimental techniques.

Results: The study successfully accomplished the absolute measurement of the reference air kerma rate for the high-dose rate brachytherapy ¹⁹²Ir radiation source. The expanded uncertainty of the measurement results was 0.72% (k = 2). The relative standard deviation for the RAKR of the same ¹⁹²Ir radiation source was 0.073%.

Conclusions: This study marks a significant advancement in the field of radiation therapy in China, particularly in the accurate dosimetry for brachytherapy using high-dose rate ¹⁹²Ir sources. The study will contribute to the BIPM.RI(I)-K8 international comparison, organized by the Bureau International des Poids et Mesures (BIPM), thus facilitating the international recognition of the measurement values.