On multicellular spheroids of variable size that were utilized as surrogates of the avascular regions within solid tumors, formed by prostate cancer cells with different expression levels of PSMA and different intrinsic sensitivities to Actinium‐225 (225Ac), we explored the killing efficacy of α‐particle radiotherapy delivered by several different radioactivity split ratios between the two carriers. The gene discussed is FOLH1; the disease is prostate cancer.