A hand-held probe for measuring radiation or magnetic activity includes a probe having a handle having a longitudinal axis and a shaft portion adapted to be inserted or held above a radiation or magnetic emitting source implanted within a patient's body or tissue of interest, the shaft portion includes a radiation or magnetic activity sensor configured to detect and measure radiation emitted from the radiation emitting source or magnetic activity from a magnetic source; the radiation emitting source being an implanted seed or a radioisotope that is injected near a tumor site in the patient's body; the probe including a signal processing device for further processing the measured radiation or magnetic activity; and a communication medium to exchange data from the hand-held probe with an external data processor unit.