Quantification of Boron Compound Concentration for BNCT Using Positron Emission Tomography

Area of Science:

• Nuclear Medicine
• Oncology
• Radiochemistry

Background:

• Boron Neutron Capture Therapy (BNCT) requires a 2 mM 10B concentration in tumors.
• Current BNCT methods use [18F]fluoro-BPA ([18F]FBPA) for treatment qualification, demanding a 3:1 tumor to background ratio.
• Thyroid cells, including cancerous ones, express the sodium-iodine symporter (NIS), which can uptake BF4-.

Purpose of the Study:

• To develop and evaluate [18F]NaBF4 as a positron emission tomography (PET) tracer for visualizing thyroids and NIS expression.
• To assess the feasibility of using [18F]NaBF4 for boron mapping in potential BNCT treatment of thyroid cancer.

Main Methods:

• Synthesized [18F]NaBF4 via isotopic exchange of 19F with 18F.
• Injected [18F]NaBF4 into rats with induced thyroid hyperplasia and tumors.
• Quantified boron concentration using PET/CT imaging (SUV) and immunofluorescence staining for NIS.

Main Results:

• Peak thyroid activity reached 9 SUVmax (2.3 MBq/mL) 17 minutes post-injection of [18F]NaBF4.
• Calculated natural boron concentration in hyperplastic thyroids reached 381 nM.
• Achieving the required 2 mM 10B concentration would necessitate an additional 110 mg/kg dose of [10B]NaBF4.

Conclusions:

• The [18F]NaBF4 PET tracer effectively visualizes thyroid NIS expression and allows for boron concentration estimation.
• This method offers advantages over current 131I treatment for thyroid cancer, including no post-treatment decay and immediate patient discharge.
• The R-BFn (1<=n<=3) labeling with 18F is a versatile approach for BNCT boron mapping and treatment.