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Region-Specific Robust Optimization for Intensity-Modulated Proton Therapy

L Liao1*, M Chen2, A Adair3, X Zhu4, W Cao5, N Sahoo6, M Yang7, B Gunn8, S Frank9, X Zhang10, (1,3,4,5,6,7,8,9,10) UT MD Anderson Cancer Center, Houston, TX, (2) Ruijin Hospital, Huangpu, Shanghai, CN

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
Conventional IMPT robust optimization algorithm assigns the same range and setup uncertainties for all targets and OARS during optimization. This may over-estimate some regions with small uncertainties and under-estimate the regions with larger uncertainties (for example, region with large anatomical change). The purpose of this work is to develop a novel region-specific robust optimization algorithm to make the IMPT plan more robust against larger anatomical change.

Methods:
A liver tumor patient with a large anatomical change in the bowel was selected for this study. This patient has 4 CTs, a primary planning CT (PCT), and three weekly verification CTs (VCTs). A region-specific robust (RSRB) plan, a Non-robust (NonRB) plan, a conventional robust (CRB) plan were created using PCT and re-calculated on each VCT. A general 2.5% range shift and 3 mm setup uncertainty was set for the CRB plan. For the RSRB plan, we placed a 15% range shift uncertainty on the bowel, 2.5% range shift on the other of OARS, and a 3 mm setup uncertainty on all regions of interest. A 60 Gy 30 fraction prescription was set on the clinical target volume (CTV).

Results:
The RSRB plan significantly improved the plan robustness of the target coverage. The CTV ?D95 (the maximum difference of the CTV D95 from dose on PCT and VCTs) and ?D98 were 1.9, and 2.4 Gy from the RSRB plan. Compare to the CRB plan, the CTV ?D95 and ?D98 were 3.3 and 4.5 Gy. The values were 8.4 and 14.1 Gy for the NonRB plan, respectively. The RSRB plan achieved a similar OAR dose level with the CRB plan.

Conclusion:
We demonstrated that region-specific robust optimization could improve plan robustness toward anatomical change. This approach has the potential to reduce the number of adaptive plans for IMPT treatment.

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