To evaluate the safety and efficacy of Boron Neutron Capture Therapy (BNCT) in patients with recurrent thoracic solid tumors that are difficult to treat with standard radiation therapy or drug therapy and are unresectable. With "lung," "heart," "liver," "spinal cord," and "esophagus" as common risk organs in the treatment plan for BNCT using therapeutic CT to evaluate the safety and efficacy of BNCT in patients with unresectable and recurrent thoracic solid tumors which are difficult to treat with standard radiation and drug therapy.

To evaluate the safety of ［18F］FBPA synthesized with MPS200FBPA. In addition, the usefulness of ［18F］FBPA-PET testing to determine the appropriateness of performing BNCT will be evaluated in an exploratory manner.

Inclusion Criteria:

• Written informed consent must be obtained from the subject.
• Patients with histopathological diagnosed malignant tumor (except cutaneous angiosarcoma)
• Measurable disease, as defined by RECIST v1.1.
• Patients diagnosed with recurrent malignant tumors that are unresectable and perceived challenging to treat with standard treatment.
• Patients with ECOG performance status score of 0 or 1.

Exclusion Criteria:

• Patients with active disease or active double cancers other than target lesions.
• Patients with imaging findings that affect imaging evaluation of the tumor, such as ground-glass opacities
• Patients who received radiation therapy exceeding 65 Gy as a prior treatment for the target lesion.
• Any serious concomitant disease that precludes completion of the study treatment.
• Patients with remaining complications of Grade 3 or higher related to prior radiation therapy in the irradiation field.