Abstract: A dermal treatment handpiece has a body with proximal and distal ends, a jet spray delivery head formed at the distal end of the body and connected to sources of a liquid suspension of a therapeutic agent and of a pressurized gas for a selectable combined supply thereof to the jet spray delivery head. The jet spray delivery head has a base formed at the distal end of the body, a localized environmental jet spray isolation chamber extending from the base to a distal exit port, a nozzle extending into the isolation chamber from the base, connected to a combined inflow of the liquid suspension and the pressurized gas, and one or more tubes mounted within the nozzle for receiving the combined inflow, each tube having a delivery tip extending into the isolation chamber for emitting a high pressure, high velocity jet spray along a delivery axis in response to receiving the combined inflow.