Evaluation of a hybrid automatic planning solution for rectal cancer

Background Script-based planning and knowledge-based planning are two kinds of automatic planning solutions. Hybrid automatic planning may integrate the advantages of both solutions and provide a more robust automatic planning solution in the clinic. In this study, we evaluated and compared a commercially available hybrid planning solution with manual planning and script-based planning. Methods In total, 51 rectal cancer patients in our institution were enrolled in this study. Each patient generated 7 plans: one clinically accepted manual plan ( planₘₐₙᵤₐₗ plan manual ), three script-based plans and three hybrid plans generated with the volumetric-modulated arc therapy technique and 3 different clinical goal settings: easy, moderate and hard ( planhybridᵉᵃˢʸ plan hybrid easy , planhybridᵐᵒᵈᵉʳᵃᵗᵉ plan hybrid moderate , planhybridʰᵃʳᵈ plan hybrid hard , planscriptᵉᵃˢʸ plan script easy , planscriptᵐᵒᵈᵉʳᵃᵗᵉ plan script moderate and planscriptʰᵃʳᵈ plan script hard ). Planning goals included planning target volume (PTV) D max , bladder D mean and femur head D mean . The PTV prescription was the same (50.00 Gy) for the 3 goal settings. The hard setting required a lower PTV D max and stricter organ at risk (OAR) dose, while the easy setting was the opposite. Plans were compared using dose metrics and plan quality metric (PQM) scores, including bladder D 15 and D 50 , left and right femur head D 25 and D 40 , PTV D 2 , D 98 , CI (conformity index) and HI (homogeneity index). Results Compared to manual planning, hybrid planning with all settings significantly reduced the OAR dose ( p < 0.05, paired t-test or Wilcoxon signed rank test) for all dose-volume indices, except D 25 of the left femur head. For script-based planning, planscriptᵉᵃˢʸ plan script easy significantly increased the OAR dose for the femur head and D 2 and the PTV homogeneity index ( p < 0.05, paired t-test or Wilcoxon signed rank test). Meanwhile, the maximum dose of the PTV was largely increased with hard script-based planning (D2 = 56.06 ± 7.57 Gy). For all three settings, the comparison of PQM between hybrid planning and script-based planning showed significant differences, except for D 25 of the left femur head and PTV D 2 . The total PQM showed that hybrid planning could provide a better and more robust plan quality than script-based planning. Conclusions The hybrid planning solution was manual-planning comparable for rectal cancer. Hybrid planning can provide a better and more robust plan quality than script-based planning.