What is the optimal number of library plans in ART for locally advanced cervical cancer?

Purpose: Library-of-plans ART is used to manage daily anatomy changes in locally advanced cervical cancer. In our institute, the library contains 2 VMAT plans for patients with large cervix-uterus motion. Increasing this number could be beneficial for tissue sparing, but is burdensome while the dosimetric gain is yet unclear. This study's aim is to determine the optimal number of plans at an individual patient level. Material and methods: Data of 14 treated patients were analyzed. Plan libraries were created containing 1-4 VMAT plans. Pre-treatment extent of uterus motion was defined by the 99th percentile of the Hausdorff distance (HD99). For dosimetric evaluations, OARs were contoured in daily CBCT scans, plan selection was simulated, and the V45Gy and V40Gy parameters were recorded. Results: Moderate to strong correlations were found between HD99 and the volume of spared OARs. All patients benefitted from adding a 2nd plan, as is the clinical practice. For patients with a HD99 between 30 and 50mm, a 3-plan library reduced the composite V40Gy with 11-21ml compared to a 2-plan library. Conclusion: Patients with large uterus motion (HD99. >. 30. mm) would benefit from an extension of the plan library to 3. HD99 is an easy-to-implement criteria to select those patients pre-treatment.

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