Abstract: The present disclosure provides lesional dosimetry methods for predicting the radioisotope activity required to deliver a therapeutic dose of radiation to induce an anti-tumor response in tumor lesions in a subject in need thereof. Specifically implemented is a computer-implemented dosimetry method comprising: detecting, in a single-time-point medical image of a patient, for each cancerous lesion of the patient, an indicator of a surrogate of a radiotherapeutic compound. The medical images captured within a predetermined time range following administration of the surrogate to the patient. Using each indicator, determining an uptake metric corresponding to uptake of the surrogate by each corresponding cancerous lesion. Generating, based on the predetermined time range and the uptake metric, using a dosimetry biomarker based on uptake of the surrogate by subjects in a cohort of subjects, a radiation dose prediction for administration of the radiotherapeutic compound to the patient.