A control circuit forms a radiation therapy treatment plan. By one approach this comprises displaying a structure dose volume histogram on a display and detecting when a user directly manipulates the displayed structure dose volume histogram. In response to detecting that manipulation the control circuit uses a corresponding virtual set of optimization objectives to optimize a radiation therapy treatment plan. If desired, the control circuit can also use weighted optimization objectives when optimizing the radiation therapy treatment plan. Also if desired, the control circuit can use only a low-resolution approximate geometry to represent a particular trajectory as corresponds to different exposure fields for the radiation therapy to be administered when initially optimizing the radiation therapy treatment plan. The control circuit can then subsequently use a high-resolution geometry to represent that trajectory to further optimize the radiation therapy treatment plan.
