We have reported novel solid-cancer treatment modality of nano-thermal ablation therapy using two medical devices of 100kHz electromagnetic field radiator and heat-generating nanoparticles of MCL particle [1]. External 100kHz electromagnetic field radiation induced heat generation of MCL particle in tumor tissue and caused tumor specific cytotoxicity and blood vessel disruption [1]. MCL particle was designed to be about 100nm diameter and to move within tumor tissue by composing heat-generating magnetite (Fe<SUB>3</SUB>O<SUB>4</SUB>) with neutral and cationic lipids [1]. However, concerning 100kHz radiator, rational concept of its performance and specification was not fully discussed. Purpose of this seminar is to describe significance of 100kHz magnetic flux density for rational designing, specification and usage of the radiator, referring to our unpublished data during 2004~2025. At first, our calibration method of 100kHz magnetic flux density was shown, and then its application to density distribution analysis of our radiators HTS-5010H and Hi-Heater 5010 was described. And, based on density distribution profile of Hi-Heater 5010 radiator, effective density at tumor locus in the standard treatment condition of the therapy was confirmed 15mT. Based on the recorded data of clinical research using HTS-5010H radiator, safety radiation condition toward groin, breast, thigh, neck, chest and arm were shown with density distribution in patient bodies. With all respect, quoting MFH<SUP>®</SUP>300F (100kHz) radiator [2], availability of three types radiators for various target cancers was discussed on the basis of effective tumor density and mitigation of normal tissue heating. According to Design Control Guidance of medical device [3], design process of the radiator was exemplified by drafted documents of design input and output.