An enhanced energy confinement regime with minimized radiative losses has been observed by controlled boronization (BZn) in the Versatile Experimental Spherical Torus (VEST), achieving without any external fueling. Previously, during the ohmic operation in VEST, the dominant radiative power losses caused by impurity influx continuously increased with the input power, reaching up to 1.4 MW, which resulted in the energy confinement time of . To suppress radiative power losses, the BZn system, employing carborane () with an expanded coverage range, is utilized as the final step in the wall-conditioning sequence. As the dose of BZn increased from 0 g to 0.2 g, the radiative losses were successfully suppressed to nearly negligible levels during ohmic discharges, eventually enhancing the energy confinement. However, as the dose increases further, the reacceleration of radiative losses is observed, suggesting that the optimal dose of BZn for radiative loss minimization is 0.2 g. Finally, the controlled BZn at the optimal point resulted in an increase in the energy confinement time by a factor of 2 compared to the 0 g dosed case. In this work, we envisage to optimize the BZn dose to minimize radiative power losses in upcoming fusion reactors.