An ultrasound beacon is incorporated into a needle of a drug delivery system utilizing high intensity ultrasound energy during certain cancer treatments. The beacon is configured to generate a electrical feedback signal in response to an initial ultrasound signal sent by an ultrasound transmitter. The electrical feedback signal is then sent along two electrical conductors of the needle and further over a cable back to the electronic unit. The feedback signal is then used to generate high intensity focused ultrasound using time-reversal acoustics principles. Therapeutic application of the system of the invention includes applying high intensity focused ultrasound at the site of drug delivery to enhance local tissue uptake of injected medication.