Evaluation of a hybrid automatic planning solution for rectal cancer

Abstract

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 ([Formula: see text]), 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 ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]). 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 D₁₅ and D₅₀, left and right femur head D₂₅ and D₄₀, PTV D₂, D₉₈, 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 D₂₅ of the left femur head. For script-based planning, [Formula: see text] significantly increased the OAR dose for the femur head and D₂ 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 D₂₅ of the left femur head and PTV D₂. 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.

Keywords: Automatic planning; Hybrid planning; Knowledge-based planning; Rectal cancer; Script-based planning.