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Online Adaptive Replanning for Sequential Boost After Whole Breast Irradiation

X Chen

X Chen*, Q Qiao, A Currey, J Nascimento, J Wilson, X Li, Medical College of Wisconsin, Milwaukee, WI

SU-E-T-597 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: For whole breast irradiation (WBI) followed by sequential boost of the lumpectomy cavity (LC), the LC shape and volume can change significantly after WBI. Consequently, the boost plan, normally generated together with WBI plan before the start of treatment, may not be optimal. Here we propose the use of online adaptive replanning at the time of boost to account for the LC change.

Methods: Daily diagnostic-quality CT sets acquired during IGRT using an in-room CT (CTVision, Siemens) for 19 breast cancer patients treated with WBI with sequential boost in prone position were used. Contours of LC, treated breast, ipsilateral lung, and heart were generated by deformably registering the planning CT with the fraction CT acquired on the first boost fraction using an auto-segmentation tool (ABAS, Elekta) with manual editing, if necessary. Three plans were generated based on the daily CT: (1) repositioning plan by applying the original boost plan with the shift, (2) adaptive plan by quickly modifying the original plan using a tool (RealArt, Prowess), and (3) reoptimization plan by a fully-blown optimization.

Results: Significant changes were observed in the LC volume and shape. The LC volume on the first day of boost changes in the range of 30% and 130% from that on planning CT. The plan quality of the adaptive plans and the re-optimization plans were comparable. Compared to the repositioning plans, the adaptive plans generally lead to improvement in target coverage and normal tissue sparing, with an average increase in LC V95 of 2.3% and decrease in breast tissue V50 of 3.0%.

Conclusion: Significant changes in LC shape and volume at the time of boost from the original plan for WBI with sequential boost can be addressed by the online replanning at the first boost fraction.

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