Authors
Jinghui Wang, Mingqing Wang, Heming 鹤茗 Wang 王, Jianfeng Lv, Bin Liu, Qiheng Li, Dongna Li, Da Fu, Kai Wang, Dongpo Fu, Hanxiang Du, Xin Xia, Bo Ma, Chaohui Ran, Wenbin Yan, Wei Gai, Kun Zhu, Hao Wang, Xueqing Yan
Published in
Physics in medicine and biology. Sep 10, 2026. Epub Sep 10, 2026.
Abstract
Intensity-modulated brachytherapy (IMBT) can improve dose conformity for rectal cancer, but current 192Ir-based systems are limited by isotropic photon emission, sequential shield motion, treatment-time penalties, and radioisotope logistics. This study designed, optimized, and characterized a dynamically shielded applicator-based intracavitary electron radiotherapy system intended to improve dose localization and enable ultra-high dose-rate delivery without a radioactive source. Approach. A cylindrical electron-beam applicator was designed with a high-density shield containing an emission window, a low-Z scatterer, and a polycarbonate guide tube. Applicator geometry was optimized using TOPAS Monte Carlo simulations to minimize radial and distal transmission factors (TFradial and TFdistal). Dosimetric performance was benchmarked against a modified Monte Carlo model based on a commercial 192Ir shielded rectal applicator (Varian GM11004160). A 3D-printed prototype with a stainless-steel shield and resin components was experimentally evaluated using a custom linear accelerator (5 MeV nominal energy, 60 mA peak current, 4 μs pulse width). Dose distributions were measured with EBT-XD radiochromic film. Main results. In the modeled homogeneous benchmark geometry, the optimized tungsten applicator achieved a radial transmission factor of approximately 1% at 10 mm from the applicator surface, compared with approximately 20% for the modeled 192Ir reference system. Distal leakage remained below 5% beyond the applicator distal end. Under modeled accelerator conditions, the electron-beam system reached approximately 100 Gy/s at 100 Hz. Superposition of single-dwell dose kernels produced both uniform fields and spatially fractionated radiotherapy patterns with valley-to-peak dose ratios ≤ 0.2. Prototype measurements demonstrated localized directional dose delivery and ultra-high mean dose rates under the reported pulse conditions, while identifying leakage pathways that caused order-of-magnitude differences from simulation. Significance. The optimized Monte Carlo model demonstrated improved radial dose localization, radioisotope-free operation, and ultra-high dose-rate capability in homogeneous geometry. Further work is needed for accelerator integration, motion control, inverse planning, and validation in anatomically realistic settings.
PMID:
42722034
Bibliographic data and abstract were imported from PubMed on 11 Sep 2026.
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