Intraoperative Breast Radiotherapy guided by X-ray Luminescent Nanoparticles

Article Outline

• Purpose/Objective(s)
• Materials/Methods
• Results
• Conclusions
• Copyright

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Purpose/Objective(s) 

Intra-operative radiation therapy (IORT) is being investigated as a single fraction alternative to multi-fractionated radiation therapy to treat surgical breast cancer margins. However, there is no method to visualize the remaining microinvasive carcinomas during surgery. We are currently investigating a new technique, X-ray Luminescent Tomography, to visualize residual disease. This technique utilizes nanoparticles, which emit optical light when irradiated with X-ray, such as that utilized in IORT. By imaging depth and extent of the tumor, this technique would give surgeons and radiation oncologists a spatial distribution of tumor extent, thus giving greater comfort with single stage breast cancer resection and radiation treatment. This study investigates the feasibility of visualizing nanoparticles at depth with an IORT radiation source within geometries relevant to breast surgery.

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Materials/Methods 

A numerical phantom was constructed of properties representative from nano-sized Gadolinium Oxysulfide phosphors doped with Europium (a red-emitting dopant), characterized in our lab. A 7x12cm rectangular phantom was implemented with typical optical properties found in the female breast. The phantom had 10mg/mL of phosphor added to cylindrical inclusions of diameters (2, 6, 10, 14mm) to simulate lesions. Phosphors were added to the background at 2mg/mL, to simulate imperfect contrast uptake. Light output was simulated for a 50keV tube voltage, similar to IORT device, and optical light was collected at a distance of 15cm from the phantom. Inclusions were placed at various depths to determine the decline in contrast with depth. Images were reconstructed using a software package designed to model the hybrid X-ray/optical physics. Recovered contrast was determined by comparing the true value of the concentration of nanoparticles with the mean recovered value in the inclusion region.

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Results 

Results showed that at a contrast of 5:1 (10mg/mL:2mg/mL), all inclusions were recovered with at least 75% accuracy at depths less than 1.5cm. As the depth increased, recovered tissue concentrations were less accurate. Concentration recovery fell below 50% beyond 1cm for the 2mm inclusion, 2cm for the 6mm inclusion, 3cm for the 10mm inclusion, and 4cm for the 14mm inclusion.

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Conclusions 

The potential of a hybrid X-ray/optical imaging system was demonstrated in a simulation study. The sensitivity of this technique is superior compared to other reflectance-based imaging modalities at depth, such as Fluorescence Molecular Imaging. Future research will focus on achieving highly specific targeting for malignant breast cancer cells. In addition, studies will focus on large-animals to determine the effectiveness of this technique.