“…It could be inferred that the nanomaterials composed of heavy metals of Gd and Hf should be suitable candidates to move to clinical trials, while the rest should be further evaluated until the biocompatibility and safety are fully estimated. The leading reasons for Hf- or Gd-based nanomaterials for use as radiosensitizers are their strong interaction with X-rays and low cytotoxicity. ,− Other characteristics that the nanomaterials or candidates should maintain for clinical use include rational nanomaterial design (e.g., size smaller than 6 nm for rapid clearance by renal, spherical, or rod shape within 20–150 nm to allow metabolism through liver, neutral and negatively charged surface or biocompatible polymer modification) to guarantee long-term biodistribution, passive or active tumor targeting, sufficient tumor accumulation, microenvironment response, and efficient clearance with minimized toxicity risks. − Notably, the applications of Cu-Cy nanoformulations for X-PDT, gold clustoluminogens for X-PDT (1 Gy), as well as the AGuIX for clinical trials indicate that metal complexes-based nanoformulations contain huge potential. Under such circumstances, we infer that Zr- or Bi-based nanoformulations might be suitable translatable candidates for X-PDT because they both have strong interactions with X-rays and can form diverse types of complexes or ultrasmall nanostructures. , Of note, the preclinical or clinical toxicity should be always evaluated beyond the general hemolysis test, hematoxylin and eosin (H&E) staining or metabolomics, , or the procedures such as genotoxicity testing, carcinogenicity testing, neurotoxicity testing, etc .…”