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A Preliminary Study of Automatic Optimization for VMAT Plans Based On Template Library

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S Xu

W Xiaoshen1 , B Qu2 , T Yang3 , X Cong4 , X Dai5 , B Liu6 , F Zhou7 , S Xu8*, (1) ,,,(2) PLA General Hospital, Beijing, BJ, (3) PLA General Hospital, Beijing, BJ, (4) PLA General Hospital, Beijing, BJ, (5) PLA General Hospital, Beijing, BJ, (6) Image Processing Center, Beihang University, Beijing, Beijing, (7) Image Processing Center, Beihang University, Beijing, Beijing, (8) Chinese PLA General Hospital, Beijing,


SU-I-GPD-J-86 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To explore the feasibility of automatic optimization for VMAT plans based on template library(TL).

Methods: VMAT plans of 68 patients for postoperative rectal cancer in Eclipse were selected. The prescription dose was 50Gy/25F. The feature values of target and OARs for 19 of 68 patients would be extracted as the vectors for each patient. All the vectors and the optimal objects would be saved as the vector library and TL, respectively. Then 15 plans(10 from TL and 5 outside TL) of rectal cancer were automatically optimized by selecting the optimal-objects template in an in-house software developed with Matlab with multi-dimensional vector similarity principle and the similarity parameter α. for the validation. The dosimetric parameters of the auto-optimized plans with the optimal-object templates(ATPs) and the Clinical plans(CPs) were compared by a paired t-test. Pearson's correlation analysis was carried out to compare the changes in the dosimetric parameters and similarity parameter α.

Results: The dosimetric parameters of ATPs for 13 plans were slightly worse than those of CPs. The difference of the conformal index (0.87vs0.89, p =0.004), heterogeneous index (1.07vs1.06, p=0.015), V40(26.92vs22.81. p=0.003) and mean dose (32.42 vs 31.3, p=0.022) of intestine were statistically significant. No significant difference for the other dosimetric parameters was seen. The α values of the 13 cases were 2.67, 2.60, 2.60, 2.49, 2.67, 2.74, 2.72, 2.48, 2.53, 2.86, 2.68, 2.56, 2.63. The strong correlations were observed between α and V40 or Dmean of bladder with a Pearson's correlation of 0.649 and 0.603. With the increase of α, V40 and Dmean of intestine for ATPs were gradually getting worse than those of CPs, and the others had an opposite trend.

Conclusion: The results of ATPs are slightly worse than those of CPs, but can fit the clinical requirements. The further study will need to be explored.

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