**7. Future prospective, challenges in radiopharmaceutical therapy**

Radiopharmaceutical targeted therapy is a promising tumor treatment, particularly α-emitter, for effective and rapid cancer therapy due to the localized cell killing originated from high LET and short ranges of particles [8, 41]. Strategies to combine α-emitter with immunomodulators demonstrated higher tumor growth inhibition than α therapy alone [44].

Furthermore, intelligent drug delivery agents apart from peptides, small molecules, mAb, and mAb fragments can also achieve target-specific cancer therapy [41]. They are among the most searched cancer treatment issues due to their desired properties, including tumor-targeting uptake, bio-compatibility, reducing sideeffects, and nonspecific uptake and distribution. So, the main problem of targeted radionuclide therapy, such as the radiation exposure effect in healthy tissues upon the emission of the particles, can be removed significantly. The number and variety of studies about the delivery of radionuclides particles by drug delivery agents are still limited. The studies will probably increase considerably in the future due to the need for effective, rapid, and personalized cancer therapy approaches.

Regarding supply issues of radionuclides also need to be address. Some main reactors in the world now are aging, which affect to constant and reliable supply globally [6]. In particular, for α-particle-emitting radionuclide (such as actinium-225), the supply is considered a potential obstacle for the growth of RPT. Some opinions suggest that the supply problems are transient technical issues that will be resolved with a more significant investment if RPT is adopted as a mainstream cancer therapy [2]. RPT is an effective cancer treatment, particularly when other standard therapeutic approaches have failed. However, even more than 40 years of clinical investigation, RPT has not become a part of cancer treatment in the same way as other therapy approaches. Even though 'targeted' cancer therapies are associated with clinical trial failure rates of 97%, but experience with RPT was ignored mainly or presented as a burdensome multidisciplinary endeavor [2, 50]. Additionally, public perception and fear of radioactivity and the perceived complexity of the treatment are challenges in developing and applying RPT.
