The study reported in the present paper aimed to evaluate the effective energy (E_eff) of X-rays emitted from the surface of a bare X-ray probe and from different spherical applicators with various diameters, which are widely employed for low kV intraoperative radiotherapy (IORT) of breast cancer. A previously validated Monte Carlo model of the INTRABEAM system along with applicator diameters of 1.5–5 cm (with 0.5 cm increments) was employed for this purpose. The results show that the presence of the applicator can considerably harden the X-rays produced by the bare probe so that E_eff increases by a factor of about 2.6. Variations of applicator diameter also affects the X-ray effective energy. Specifically, increasing the applicator diameter from 1.5 to 3 cm and 3.5–5 cm resulted in an increase in the E_eff by 8.8% and 14.6%, respectively. The validity of the calculated E_eff values was confirmed by a reasonable agreement between the obtained probability density distributions (PDDs) for the full X-ray energy spectrum and those for the corresponding single effective energies, for different applicator diameters. The E_eff values obtained for different applicator diameters and the bare probe alone can be used as an alternative for the corresponding full energy spectra, in Monte Carlo-based dosimetry simulations of low-energy therapeutic X-rays, as well as for determining quality conversion factors of any ion chambers employed for low kV-IORT absolute dosimetry.

本文报道的研究旨在评估裸露的X射线探头表面和不同直径的不同球形敷料器发出的X射线的有效能量（E _eff），这些能量被广泛用于低kV术中放疗（IORT）的乳腺癌。为此，使用了先前验证的INTRABEAM系统的蒙特卡洛模型以及1.5–5 cm（增量为0.5 cm）的涂药器直径。结果表明，涂​​药器的存在可以大大增强裸探头产生的X射线，从而使E _eff增加了约2.6倍。施加器直径的变化也会影响X射线有效能。具体来说，将喷枪直径从1.5厘米增加到3厘米和3.5-5厘米，分别会使E _eff增大8.8％和14.6％。对于不同的喷头直径，通过完整的X射线能谱的概率密度分布（PDD）与相应的单个有效能量的概率密度分布（PDD）之间的合理协议，_可以确定所计算的E _eff值的有效性。电子_EFF 在低能治疗性X射线的基于Monte Carlo的剂量学模拟中，以及用于确定任何质量转换因子时，可以将针对不同施药器直径和裸露探头获得的值分别用作对应的全能谱的替代方法。用于低kV-IORT绝对剂量的离子室。