Room: Karl Dean Ballroom A1
Purpose: Radiation plan quality and organ at risk (OAR) sparing varies considerably between planners. An a priori estimation tool for best possible sparing of OARs called Feasibility DVH(FDVH) may reduce OAR dose and plan quality variation. We introduced the FDVH tool clinically for head and neck treatment planning to determine its impact on plan quality metrics (OAR sparing and target conformity and heterogeneity).
Methods: Radiation plans from ninety-four patients with oropharynx cancer treated on clinical trials from February 2012 to September 2017 were reviewed. All patients received VMAT or Helical delivery. Patients were categorized into two cohorts based on the use of FDVH tool during planning (FDVH cohort vs. Baseline cohort). The assessed organs at risk were the contralateral parotid and larynx. FDVHs for the baseline cohort were retrospectively generated for comparison. The difference in the mean OAR doses were compared between the planned and the â€œbest possible sparingâ€? FDVHs. This metric allows for analysis of dose reduction across patients by adjusting for OAR/target geometry. Planning target volume (PTV) conformity indices (CI) and homogeneity indices (HI) were also compared between cohorts.
Results: The use of FDVH yielded a significant decrease of 4Gy and 4.5Gy for the contralateral parotid and larynx, respectively (p<0.001). Patients planned with FDVH had statistically higher conformity indices for both the high risk (0.87 vs 0.81; p <0.001) and standard risk (0.78 vs 0.76, p=0.04) PTVs, but also higher homogeneity indices (0.046 vs. 0.038; p<0.001). In addition, the use of the FDVH tool reduced the variance between the planned and best possible FDVH mean dose for the contralateral parotid (p=0.035).
Conclusion: The prospective use of the FDVH tool during planning led to decreases in the mean dose delivered to the contralateral parotid and larynx. This tool also significantly decreased the variation in contralateral parotid dose sparing.