Review: Phosphorus-33 - Analysis of nuclear reactor production methods for potential application in radionuclide therapy for bone metastases.

Phosphorus-33 (33P) has attracted growing interest as an alternative to phosphorus-32 (32P) for targeted radionuclide therapy. Its longer half-life (25.3 vs. 14.3 days), lower maximum beta energy (∼0.25 MeV vs. 1.7 MeV), and shorter median tissue penetration depth (0.135 mm vs. 3.65 mm) may make it particularly suitable for treating conditions such as bone metastases, where minimizing collateral damage to radiation-sensitive structures like red bone marrow is critical. Despite these advantages, preclinical assessment and implementation of 33P has been limited by production challenges. This review examines both experimental and theoretical production pathways for high-purity 33P, emphasizing methods that avoid and minimize co-production of 32P. Such approaches reduce purification burdens and preserve useable 33P activity by eliminating decay delays. This review considers target material selection, reaction cross sections, and irradiation modality. Among the five pathways evaluated, the 33S(n,p)33P reaction is identified as the most feasible for producing 33P, though its application depends on advances in 33S enrichment to avoid significant 32P contamination from the competing 32S(n,p)32P reaction.