Inclusion Criteria:  prior radiotherapy of the treatment side with a treatment dose > 30 Gray (Gy) EQD2 (calculated with alpha/beta value of 9) local/ regional / or oligometastatic tumor recurrence. Maximum number of three macroscopic tumor lesions with at least one of them receiving prior radiotherapy macroscopic tumor recurrence side of recurrence is amenable to hyperthermia (abdomen, pelvis, extremities, spine, cervical lymphnodes) planned re-irradiation dose of at least 40 Gy EQD2 (calculated with alpha/beta value of 9)  Exclusion Criteria:  >3 macroscopic tumor lesion brain metastases recurrence is amenable to local ablative radiotherapy (brachytherapy or stereotactic radiotherapy) recurrence region is not amenable to hyperthermia (lung, liver, mediastinum) contraindications for hyperthermia (serious cariovascular disease, ICD or larger implants at the treatment site) psychiatric disorders that impede proper informed consent serious comorbidities with very limited prognosis quo ad vitam