(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: To investigate the impact of objective goal values on dose-volume histogram (DVH) metrics used for treatment plan optimization.
Methods: For this study, ten prostate cancer patients were selected. Each patient plan was optimized for volumetric modulated arc therapy (VMAT) using 2 full arcs in the Pinnacle treatment planning system (TPS). Target volumes and the organs at risk (OAR) were segmented by the same physician. The prescription doses for each patient and the dose volume objectives for each OAR were also specified by the same physician. For each patient, a plan was created with the specified dose volume objectives and was used as the reference plan. Then eight plans were created by either decreasing or increasing the Rectum and Bladder dose volume objectives by 50 cGy. All plans had the same prescription dose, beam arrangement, and dose calculation resolution. The number of optimization iterations remained the same for each plan without user interference. DVH, conformity and homogeneity indices and isodose distributions were used for the comparison of each plan.
Results: Our results showed that for the majority of the patients, the plan optimized with decreasing both rectum and bladder objectives (R&BL) were comparable to the reference plan in terms of conformity (1.12 vs 1.15) and homogeneity (1.058 vs.1.059). The Rectum and Bladder objective goals for R&BL plan were reduced by 0.09% to 3.95%. Overall the majority of the objective goal doses were reduced by 0.09% to 11.79% for the plans with 50cGy dose decreased for either Rectum or Bladder objective goals.
Conclusion: The plans with the dose decreased for both Rectum and Bladder objective goals, illustrated improvement of normal tissue sparing while achieving similar target dose distribution compared to the reference plan. Further investigation is required to determine the magnitude of improvement.
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