Program Information
How Many and Which Respiratory Phases Should Be Included During the 4D Robust Optimization Process
S Ge1*, X Wang2 , R Mohan3 , (1) M.D. Anderson Cancer Center, Houston, TX, (2) MD Anderson Cancer Center, Houston, AA, (3) UT MD Anderson Cancer Center, Houston, TX
Presentations
SU-F-T-120 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To study how many and which respiratory phases should be included to conduct an efficient 4D robust optimization since contouring CTV and critical organs at all 10 phases are time consuming.
Methods: A 4D robust optimization algorithm which simultaneously optimizes dose distributions for all 10 respiratory phases has been developed to desensitize plan quality to various uncertainties. To study the possibility of reducing number of phases included during the optimization process while keep the plan quality, four strategies have been conducted and compared: A. including 2 phases: 0% and 50%; B. including 4 phases: 0%, 20%, 50% and 80%. C. including 5 phases: 0%, 20%, 50%, 60% and 80%; D. including all 10 phases during the optimization process. The resulting plans for two patients were evaluated at all 10 respiratory phases.
Results: For patient one, reducing the number of phases included in optimization process will degrade CTV coverage while improve the normal tissue sparing. The possible worst CTV coverage at prescription dose (74Gy) for IMPT plans optimized for strategy A, B, C, D was 98.13%, 98.29%, 99.00% and 99.05% respectively. The CTV coverage is almost the same when including 5 phases compared to including 10 phases. For patient 2, reducing the number of phases included in optimization process will degrade CTV coverage, while the normal tissue sparing is not affected too much. The possible worst CTV coverage at prescription dose for IMPT plans optimized for strategy A, B, C, D was 95.85%, 99.01%, 99.18% and 99.72% respectively. The CTV coverage is similar when including 4 phases or 5 phases compared to including 10 phases.
Conclusion: The preliminary data shows that at least 4 phases or 5 phases should be included during optimization process to achieve a high quality IMPT plan considering CTV coverage and normal tissue sparing.
Funding Support, Disclosures, and Conflict of Interest: No conflict
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