Ponente
Descripción
Operating medical linear accelerators (LINACs) above 6 MV generates unwanted neutrons through (γ,n) interactions with high-Z materials in the accelerator head. These secondary neutrons contribute additional dose to healthy tissues and may lead to late-onset adverse effects [1]. Moreover, the neutron yield shows high variability, depending on several factors, e.g., LINAC model, beam energy, and delivery modality. Consequently, real-time, patient-specific neutron characterization is essential for accurate assessment of secondary exposure and for optimized radiation safety measures.
To address this challenge, IMB-CNM has developed an ultra-thin (20 μm) neutron sensor based on silicon with an innovative 3D architecture coupled to a (45 ± 5) μm thick ¹⁰B-enriched conversion layer to quantify thermal neutron fields. The ultra-thin active volume provides a high gamma-rejection factor (>10⁻⁸), crucial for isolating neutron signals in high-gamma-ray environments. Custom readout electronics enabled online acquisition.
Real-time thermal neutron contributions were measured in two treatment rooms comparing two widely used LINACs—Varian TrueBeam and Elekta Synergy—operated with flattened (FF) 15 MV X-ray beams and 10×10 cm² field size. Measurements were compared against PHITS Monte Carlo simulations using an extended 15 MV TrueBeam head model that, for the first time, includes detailed head shielding and was validated with PDD data (TPR20,10 difference <1.3%, see Figure 1) [2]. A neutron distribution map throughout the treatment room was also simulated (Figure 2).
The sensors reliably characterized the thermal neutron field, achieving a detection efficiency of (1.53 ± 0.02)% at a 660 keV energy threshold and operating without interference from the intense photon background and without saturation effects up to the maximum dose rate 600 MU min-1 (Figure 3). The secondary neutron field produced by the Varian TrueBeam was approximately four times higher than that of the Elekta Synergy throughout the room and under similar conditions in agreement with the literature [3].
Ongoing work focuses on optimizing the conversion layers to enhance efficiency and on developing a new portable neutron spectroscopy system for more accurate total neutron dose estimation.
References
[1] Banaee, et al. (2021). Journal of Radiation Research, 62(6), 947-954.
[2] Zamorano, et al. (2025). Phys. Med. Biol, 70(16), 5001.
[3] Belousov, et al. (2020). Radiation Protection Dosimetry, 188(2), 145-152.
