Development and clinical validation of Knowledge-based planning for Volumetric Modulated Arc Therapy of cervical cancer including pelvic and para aortic fields.

Abstract

Knowledge-based planning (KBP) is based on a model to estimate dose-volume histograms, configured using a library of historical treatment plans to efficiently create high quality plans. The aim was to report configuration and validation of KBP for Volumetric Modulated Arc Therapy of cervical cancer. A KBP model was configured from the institutional database (n=125), including lymph node positive (n=60) and negative (n=65) patients. KBP Predicted plans were compared with Clinical Plans (CP) and Re-plans (Predicted plan as a base-plan) to validate the model. Model quality was quantified using coefficient of determination R2, mean square error (MSE), standard two-tailed paired t-test and Wilcoxon signed rank test. Estimation capability of the model was good for the bowel bag (MSE=0.001, R2=0.84), modest for the bladder (MSE=0.008) and poor for the rectum (MSE=0.02 R2=0.78). KBP resulted in comparable target coverage, superior organ sparing as compared to CP. Re-plans outperformed CP for the bladder, V30 (66±11% vs 74±11%, p<.001), V40 (48±14% vs 52±14%, p<.001), however sparing was modest for the bowel bag V30 (413±191cm3 vs 445±208cm3, p=.037) V40 (199±105cm3 vs 218±127cm3, p=.031). All plans were comparable for rectum, while KBP resulted in significant sparing for spinal cord, kidneys and femoral heads. KBP yielded comparable and for some organs superior performance compared to CP resulting in conformal and homogeneous target coverage. Improved organ sparing was observed when individual patient geometry was considered.