Boron neutron capture therapy as salvage treatment for recurrent papillary thyroid carcinoma-a case report

A 69-year-old man diagnosed with left papillary thyroid carcinoma underwent partial thyroidectomy on July 18, 2017. Follow-up positron emission tomography (PET) revealed a residual tumor in the left thyroid bed, so he received salvage tomotherapy with 5,500 centigray (cGy) in 29 fractions, from September 21 to November 3, 2017. The patient also took adjuvant radioactive iodine (RAI)-131 twice. Nonetheless, follow-up imaging on June 29, 2018 revealed a residual lesion on the left side of the anterior neck. Boron neutron capture therapy (BNCT) for salvage management was performed at the Tsing-Hua Open Pool Reactor (THOR) on October 8, 2018. The patient received a total dose of 450 mg/kg of L-[4- 10borophenylalanine] fructose via continuous intravenous infusion. The blood boron concentration was 21.27 ppm at 2 hours post-infusion just before epithermal neutron irradiation. Mean, minimal and maximal doses of gross tumor volume (GTV) were 22.36, 19.83 and 23.60 gray equivalent (GyE), respectively. One month after BNCT, PET/magnetic resonance imaging (MRI) revealed regression of the recurrent tumor, with the maximum standardized uptake value decreasing from 17.8 to 11.7. Thyroglobulin also dropped significantly, from 55.6 to 15.1 ng/mL. The patient reported no significant side effects after BNCT. So far, most investigations have been confined to applying BNCT on patients of recurrent head and neck or brain tumor. In this study, we had the opportunity to present the outstanding treatment results of BNCT in a patient with recurrent thyroid papillary carcinoma in Taiwan. Based on the case outcome, BNCT can be used as salvage treatment for recurrent or refractory thyroid cancer.