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Dosimetric Impact of Optimization Resolutions Using the New Photon Optimizer Algorithm in Eclipse Treatment Planning System

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S Li

Sha Li, Meijiao Wang, Yibao Zhang*, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), Department of Radiation Oncology, Peking University Cancer Hospital & Institute, Beijing 100142 China. *Corresponding author.


SU-I-GPD-T-334 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Based on the new Photon Optimizer (PO) of Eclipse V13.5, this study investigates dosimetic effects of different optimization resolutions on knowledge-based planning for preoperative rectal cancer patients.

Methods: A validated RapidPlan model was applied to estimate the DVHs for 20 patients using all three allowable resolutions of 1.25mm, 2.50mm and 5.00mm respectively. API script compared the predicted DVH ranges (upper and lower borders) and generated optimization objectives using various resolutions. Based on identical objectives but various optimization resolutions, three plans for each patient were created and compared respectively. All other parameters were maintained such as dose-volume calculation grid size (2mm). Metrics of interest were extracted from exported Dose Volume Histograms (DVH) in tabular format, which were also used to calculate mean DVHs of 20 patients using an in-house MATLAB code. Plotting and statistical analysis were performed using SigmaPlot and SPSS respectively.

Results: Resolution does not affect DVH prediction and optimization objective generation. Based on identical optimization objectives, the impact of resolution on target dose resolution was negligible (difference of mean dose ≤0.02 Gy). Noticeable yet insignificant varieties of OAR dose were induced by various resolutions: resolution of 2.50mm achieved lowest bladder V45Gy V35Gy, V40Gy, and small bowel mean dose; intermediate femoral head mean dose and bladder V40Gy were also yielded by 2.50mm. Finest resolution of 1.25 mm was superior in femoral head mean dose, bladder V40Gy, and bladder mean dose, yet at cost of approximately 3-folds and 5-folds longer time for optimization than 2.50 mm and 5.00mm respectively. Optimization resolution of 2.50mm was most cost-effective.

Conclusion: Finest optimization resolution of 1.25mm does not necessarily yield plans of best quality, yet costs much longer time. For cost-effectiveness, optimization resolution of 2.50mm is recommended for clinical planning using PO.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by Beijing Natural Science Foundation (7172048), National Natural Science Foundation of China (11505012), and Beijing Municipal Administration of Hospitals' Youth Programme (QML20151004).

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