Multiadaptive Plan (MAP) IMRT to Accommodate Independent Movement of the Prostate and Pelvic Lymph Nodes.

摘要

Because of the challenge of the independent movement of the prostaterelativeto the lymph nodes, this research is to develop a novel method using multi-adaptive plan (MAP) IMRT to accommodate independent movement of the two targeted tumor volumes. In this project, we evaluated two adaptive strategies: strategy A creates a set of IMRT plans individually optimizing on a series of possible prostate positions in the planning CT; and strategy B creates a set of multi-adaptive plans by dynamically adjusting the radiation apertures to accommodate the daily position of the prostate. Using dual imaging registration method, we found that the bi-directional prostate movement in relative to the pelvic lymph nodes, particular in anterior-posterior and superior-inferior directions, must be considered with strategy A, which increases the number of prepared IMRT plans. Using implanted markers as a surrogate for the location of the prostate gland may mis-interpret the rotation of the gland and a special caution is needed when a large rotation is detected. The prostate rotation can be compensated with translational shifts of the radiation portals. With current clinical planning margins of 8mm/6mm posterior to the prostate and 5 mm to the pelvic lymph nodes, the MLC tracking strategy is not necessary. Further reduction in the planning margins to the both targets may require MLC tracking method or real time planning.