Blue Shield of California, a San Francisco-based health insurer, has adopted a policy to approve payment for medically necessary treatment of mild-to-moderate psoriasis using the Xtrac laser system produced by PhotoMedex Inc. of Montgomeryville, Pa. Similar policies have been issued by Blue Cross Blue Shield plans in other states. As a result of increased demand for the system, the Pennsylvania company intends to expand its sales force by more than 50% in 2008.