A Priori Knowledge of Maximum Achievable Organ at Risk Sparing: Impact on Organ Doses and Patient Reported Outcomes.

Abstract

PURPOSE/OBJECTIVE(S)\nIMRT planning is challenging, at least in part, due to the essentially-infinite number of possibilities, and since the planner is never sure that they have gotten the best , or at least nearly the best achievable plan. We prospectively assessed the impact of providing IMRT planners with a priori knowledge of the maximum achievable dose sparing for organs at risk (OARs) for patients on both dosimetric and clinical endpoints. We hypothesized that a priori knowledge of maximum achievable sparing would improve dosimetric and clinical (i.e., patient reported outcome) measures.\n\n\nMATERIALS/METHODS\nWe examined patients receiving IMRT for oropharynx cancer on prospective clinical trials from 2012-2019 at our institution. A tool that generates estimates of maximum achievable dose sparing for organs at risk was used starting July 2016. Patients treated pre-implementation (i.e., baseline) and post-implementation (i.e., experimental) were compared for the endpoints: (1) Doses received by various OARs MINUS doses achievable (per the tool), termed the excess of feasible dose ; (2) Plan quality metrics (e.g., target homogeneity and conformity), and (3) Patient reported outcomes (PRO) per questionnaires completed at 3-, 6- and 12-months post-treatment.\n\n\nRESULTS\n139 patients were analyzed (60-baseline cohort, 79-experimental). (1) The excess of feasible dose was lower in the experimental (vs baseline) cohort, for the contralateral parotid (9.6 vs 5.5 Gy; P < 0.001), the ipsilateral parotid (17.6 vs 6.8 Gy; P < 0.001), larynx (12.5 vs 8.2 Gy; P\u202f=\u202f< 0.001), oral cavity by (15.8 vs 14.3 Gy; P\u202f=\u202f0.002), and contralateral submandibular gland (17.4 vs 17 Gy; P\u202f=\u202f0.40). Lesser variation of excess of feasible dose (i.e., more consistent sparing) was seen in the experimental (vs. baseline) cohort for the parotid and contralateral submandibular glands (P < 0.05). (2) Some small differences in target homogeneity and conformity were observed but not felt to be clinically significant. (3) The average post-RT PROs were significantly better in the experimental cohort vs baseline at 6 months post-RT. Dry mouth severity, sticky saliva, meal enjoyment, severity of pain, and EAT10 composite (swallowing) were all significantly improved; P < 0.05).\n\n\nCONCLUSION\nClinical plans aided by an a priori estimate of maximum achievable dose sparing for OARs was associated with improved (and more consistent) OAR sparing and better clinical outcomes (i.e., better post-RT PROs). Clinical implementation of this tool can yield quantifiable dosimetric and patient benefits.