Prospective multi‐institutional study of library‐based adaptive radiotherapy for cervical cancer: Evaluation of plan‐of‐the‐day selection and population analysis

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PURPOSE: Plan-of-the-day (PoD) adaptive radiation therapy (ART) is based on a library of treatment plans, with 3D daily imaging guiding the plan selection. In a phase II multi-institutional trial of cone-beam CT (CBCT)-guided PoD-ART for locally advanced cervical carcinoma (LACC), this study aimed at evaluating the PoD selection, its geometric and dosimetric impact and characterizing a sub-population of patients associated with dosimetric improvement from ART. MATERIAL AND METHODS: For 49 cervical cancer patients, three planning CT scans [empty bladder (EB), intermediate bladder (IB) and full bladder (FB)] were acquired to generate a treatment plan library. A dose of 45 Gy was prescribed to the planning target volume in 25 fractions. Daily CBCT were acquired to visually select the best plan in the library (Manual-ART strategy). A deep learning model was used to segment daily clinical target volume (CTVt) and organs-at-risk (OAR). Manual-ART was compared to two strategies: (i) "Non-ART" strategy (IB-CT treatment plan only); (ii) PoD-ART strategy selecting the PoD maximizing CTVt coverage ("Cov-ART"). Geometrical and dosimetric coverages of daily CTVt and OAR were assessed. Decision trees were developed to predict the subpopulation of patients associated with dosimetric benefit from PoD-ART. RESULTS: The agreement in PoD selection between Manual-ART and Cov-ART was 63.5%. Compared to the Non-ART strategy (D95%-CTV: 43.6 ± 4.1 Gy), PoD-ART significantly increased the dose to the target, with Manual-ART achieving 44.0 ± 3.0 Gy and Cov-ART with 44.1 ± 2.0 Gy. Decision trees using IB-CT plan and first two treatment fractions correctly classified 85.4% and 93.8% of patients as benefiting or not from PoD-ART. CONCLUSIONS: In PoD-ART for LACC, selected treatment plans by the radiation oncologist had 63.5% concordance with treatment plans maximizing target coverage. PoD-ART increased dose to target, without compromising dose to OARs, with the largest benefit observed in a sub-population identifiable after two treatment fractions.

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