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Robust Optimization Lung Treatment Plans Accounting for Geometric Uncertainty

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X Zhang

X Zhang*, J Penagaricano , J Fang , G Narayanasamy , S Maraboyina , F Xia , L Peacock , C Croft , S Morrill , University of Arkansas for Medical Sciences, Little Rock, AR


SU-I-GPD-T-509 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate RayStation internal target volume-based robust optimization planning method (ITV-Robust) in photon lung treatment plans and to conduct a dosimetric study by comparing ITV-Robust plans with margin-based PTV-IMRT and PTV-VMAT plans.

Methods: Twenty lung cancer patients were selected. Ten-phase 4DCT (0% to 90%) image data sets were acquired for each patient. An ITV contour was derived based on 10 individually contoured GTVs generated on each image phase. Maximum tumor motion range was 0.3cm to 2.7cm. ITV-Robust plans were generated by creating case scenarios based on set-up uncertainty margins by user. These margins are optimized by the RayStation-TPS by minimizing the worst case scenario. The uncertainty margins used in this study were 0.5cm for left/right, 1.0cm for superior/inferior and 0.5cm for anterior/posterior direction based on RTOG 0236 and 0915 protocols. Margin-based PTV-IMRT and PTV-VMAT plans were also generated using the same beam and dose optimization setup. Dose was prescribed to 95% of the ITV or PTV to receive 60Gy in 8 fractions. ITV target doses(Dmean, D95), Paddick’s conformity index (CI), homogeneity index (HI), MU and OAR doses were compared using a multivariate ANOVA statistical test.

Results: ITV target coverage D95 satisfied the prescription dose for all compared plans. The median and range of the Dmean was 61.71(61.05-66.43)Gy for ITV-Robust, 62.55(61.21-83.3)Gy for PTV-IMRT, and 63.66 (61.82-78.74)Gy for PTV-VMAT plans. HI was in good agreement (p>0.05) for all plans. However, ITV-Robust plans produced significantly higher CI values, lower OAR doses and lower MU in every compared case (p<0.001).

Conclusion: CI values, MUs and OAR sparing were improved with similar ITV dose coverage and HI values for ITV-Robust compared to margin-based PTV-IMRT and PTV-VMAT plans. Because of the smaller target volume, the robust optimization method will be of benefit for tumors with substantial motion, especially those tumors near or abutting critical organs.

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