The impact of avoidance sectors on knowledge-based planning for esophageal cancer treatment

To build a knowledge-based treatment planning model using RapidPlan for esophageal cancer in the upper, mid and lower thoracic sites while comparing the performance of the model with and without the use of avoidance sectors. Plans from 45 patients with esophageal tumors requiring treatment in the upper (8), middle (15) and lower (22) thoracic regions were selected for training. Prescribed dose ranged from 41.4Gy to 56Gy (1.8-2 Gy/fraction) with simultaneous integrated boost (SIB). Clinical plans were re-planned without the use of avoidance sectors. Plans with reduced V105%(cc) to the planning target volume (PTV) while meeting criteria for organs at risk (OARs) were chosen to build the model. The model was validated on 23 plans by comparing the clinical plan to the RapidPlan with and without the use of avoidance sectors. RapidPlan without avoidance sectors reduced the V105%(cc) by 100.1 cc (p< 0.001), compared to the clinical plan, while also reducing the maximum dose. The lung V5 Gy was increased by 5.5% on average (p = 0.02). Doses to the heart, stomach, kidney, large bowel, small bowel and the spinal cord were not compromised. Using avoidance sectors with RapidPlan did not improve plan homogeneity or coverage over the clinical plan, while increasing the V20 Gy to the lungs by 2.8% (p = 0.01). Mean heart dose was increase by 1.1 Gy (p = 0.04), while kidney V18Gy (%) and spinal cord maximum were increased by 7.2% (p = 0.02) and 3.8 Gy respectively (p = 0.01). Volume of the prescription dose outside the PTV was lower by as much as 67 cc while using RapidPlan without avoidance sectors compared to the clinical plan and conformity index (CI) was improved by 7%-8% compared to the clinical plan. Using avoidance sectors worsened the CI by 3%-5% compared with the CP. The RapidPlan model configured for upper, mid and lower thoracic regions without the use of avoidance sectors significantly reduces volumes of the higher doses in the target and therefore potential likelihood of esophageal toxicity without excessively increasing lung dose.