[Paper Review] First Pilot Tests of Compton Imaging and Boron Concentration Measurements in BNCT Using i-TED

J. Lerendegui-Marco, J. Balibrea-Correa+11 more|arXiv (Cornell University)|Sep 9, 2024

Boron and Carbon Nanomaterials ResearchMaterials Science3 citations

TL;DR

This study demonstrates the first real-time, in-vitro application of the high-efficiency Compton camera i-TED for measuring boron-10 concentration and imaging spatial dose distribution in BNCT. Using 478 keV gamma rays from the 10B(n,α)7Li reaction, i-TED achieved sub-microgram sensitivity (≤1 μg 10B) and successfully reconstructed 2D Compton images of cell samples, proving its potential for online, non-invasive dosimetry in BNCT.

ABSTRACT

Dosimetry in BNCT poses significant challenges due to the indirect effect of neutrons interacting with elements within the body and uncertainties associated with the uptake of boron compounds used in clinical practice. Current treatment planning relies on unconventional estimates of boron tumor uptake derived from prior PET scans and thus, an online boron-uptake monitor would be highly convenient. This work presents the first pilot experiments carried out at ILL-Grenoble with the high-efficiency Compton camera i-TED, hereby aiming at demonstrating its applicability for BNCT dosimetry by introducing real-time measurement of the boron concentration and imaging capabilities of spatial dose distribution. In this experiment, we measured the $^{10}$B uptake of different cancer cells of tongue squamous cell carcinoma, malignant melanoma and glioblastoma treated with BPA (80~ppm of $^{10}$B). The samples were irradiated with the thermal neutron spectrum of ILL-Grenoble and the 478keV $γ$-rays from the $^{7}$Li de-excitation after the neutron-boron reaction were registered both with the Compton imager and the high-sensitivity FIPPS HPGe array. These series of measurements allowed us to demonstrate the imaging capabilities of the Compton imaging device for the 478 keV $γ$-rays of interest for dosimetry in BNCT, as well as to assess its sensitivity, which was found to be below 1 $μ$g of $^{10}$B.

Motivation & Objective

• To demonstrate the feasibility of real-time, in-vitro boron-10 concentration monitoring during BNCT using Compton imaging.
• To evaluate the sensitivity and imaging performance of the i-TED Compton camera for detecting 478 keV prompt gamma rays from the 10B(n,α)7Li reaction.
• To validate i-TED's quantitative accuracy by comparing its 10B measurements against the high-sensitivity FIPPS HPGe array.
• To establish a foundation for future clinical application of Compton imaging in online BNCT dosimetry.
• To assess the robustness of i-TED in low-background conditions with biological samples containing trace boron.

Proposed method

• Irradiated tongue squamous cell carcinoma (CAL33), glioblastoma (A172), and malignant melanoma (A375) cell lines with BPA at 80 ppm 10B using the thermal neutron beam at ILL-Grenoble (5×10⁷ n/cm²/s).
• Simultaneously detected 478 keV gamma rays using the i-TED Compton camera and the high-sensitivity FIPPS HPGe array as reference.
• Employed a four-crystal LaCl₃-based Compton camera with GPU-boosted reconstruction algorithms to enable real-time image reconstruction.
• Applied Compton kinematics to reconstruct the emission point of 478 keV photons using energy and position measurements from scatter and absorber detectors.
• Used Monte Carlo simulations to support performance evaluation and optimize detection efficiency.
• Performed background subtraction and signal extraction to isolate the 478 keV line from residual radiation and neutron interactions.

Experimental results

Research questions

• RQ1 Can the i-TED Compton camera detect 478 keV gamma rays from the 10B(n,α)7Li reaction with sufficient sensitivity for in-vitro BNCT dosimetry?
• RQ2 What is the minimum detectable 10B concentration using i-TED in a low-background, high-neutron-flux environment?
• RQ3 Can i-TED produce spatially resolved 2D images of 478 keV emission from boron-loaded cell samples?
• RQ4 How does the i-TED measurement of 10B concentration compare quantitatively to the gold-standard FIPPS HPGe array?
• RQ5 Is i-TED robust enough to resolve boron distribution in complex biological samples with minimal background interference?

Key findings

• The i-TED Compton camera achieved a detection sensitivity of ≤1 μg of 10B, demonstrating its capability to detect trace boron concentrations relevant to BNCT.
• 2D Compton images of cell samples containing a few micrograms of 10B were successfully reconstructed, even in the presence of boron-related background.
• i-TED measurements of 10B concentration in cell samples showed consistent results when compared to the high-sensitivity FIPPS HPGe array.
• The system demonstrated real-time capability due to GPU-optimized reconstruction algorithms, enabling dynamic monitoring of boron uptake during irradiation.
• The high efficiency of the LaCl₃-based i-TED detector, combined with low neutron sensitivity, makes it suitable for clinical BNCT environments.
• This work represents the first experimental demonstration of Compton imaging for 478 keV gamma rays in BNCT, validating its potential for online dosimetry.