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Building Atlas for Automatic Prostate IMRT Planning: Anatomical Feature Parameterization and Classification

Y Sheng

Y Sheng1*, T Li2 , Y Zhang3 , F Yin4 , Y Ge5 , Q Wu6 , (1-4,6) Duke University Medical Center, Durham, NC, (5) University of North Carolina at Charlotte, Charlotte, NC


MO-C-17A-7 Monday 10:15AM - 12:15PM Room: 17A

Purpose: To establish and evaluate a prostate IMRT plan atlas to provide accurate dose guidance for dose-guided automatic planning (DAP) technique.

Methods: 25 prostate cancer patients treated with IMRT were studied. The anatomy of prostate cancer cases was parameterized and quantified into two measures: the percent distance-to-prostate (PDP) and the concaveness angle. Patients were represented by points at a 2D space spanned by the two anatomical measures. The k-medoids algorithm was used to elect k cases from 25 points to compose the atlas. To determine the optimal size k, the average silhouette width for each k-medoids scheme was calculated and the k corresponding to higher average silhouette width was chosen as the atlas size.

The other cases were used as query cases to evaluate the atlas efficacy. The DAP technique, which links atlas and query case using deformable image registration, was used to generate the automatic IMRT plan. Dosimetric comparison between DAP plans and clinical plans were performed.

Results: Atlases of sizes ranging from 2 to 9 are established. The average silhouette width for each atlas of the size from 2 to 9 is 0.651, 0.558, 0.455, 0.563, 0.620, 0.580, 0.636, and 0.695, respectively. The size of 6 is preliminary chosen as the optimal size for robustness test. Dosimetric similarities are observed between two plans (p>0.05): homogeneity indices are 6.7±1.2% and 7.3±1.6%; rectum-gEUDs are 40.6±1.8 Gy and 40.6±2.1 Gy, for DAP plans and clinical plans, respectively. Improved conformity index and bladder-gEUD are observed in the DAP plan (p=0.036, 0.009 respectively).

Conclusion: An atlas with 6 expert prostate IMRT plans was identified as the optimal size. DAP plans generated with the dose guidance from the atlas show comparable plan quality with clinical plans. The atlas can cover various anatomical configurations and provide satisfying dose guidance when implemented with the DAP technique.

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