According to some embodiments, systems for energy delivery to targeted tissue comprise a catheter with an ablation member, a radiometer configured to detect temperature data from the targeted tissue, a processor configured to determine a calculated temperature (e.g., an extreme temperature, such as a peak or trough temperature) within the tissue by applying at least one factor to the temperature data detected by the radiometer, the processor configured to compare the calculated temperature to a setpoint and an energy source configured to energize the ablation member and to regulate delivery of ablative energy to the targeted tissue of the subject based at least in part on the comparison. In some embodiments, the factor depends on at least one characteristic of the targeted tissue. Information regarding a tissue characteristic can be provided using information from an imaging set (e.g., intracardiac echo) or an electrical signal of the subject (e.g., electrocardiogram).