Physician Driven Multicriteria Optimization of Advanced Lung Cancer Patients VMAT Plans

Abstract

Multi-Criteria Optimization (MCO), a novel commercially available optimization method for intensity modulated and volumetric arc therapies (IMRT and VMAT) has the potential to improve treatment planning techniques and workflows. By navigating between Pareto solutions, MCO allows planners and physicians to assess in real time the impact and tradeoffs between all clinical goals and organ constraints. The purpose of our work is to investigate a universal set of objectives and constraints for lung cancer MCO VMAT plans and the impact of involving the Physician in the navigation of the generated Pareto plans. The central hypothesis is that physician-driven MCO VMAT plans will allow choice of optimal dosimetric trade-offs for a given individual patient. We randomly selected ten lung cancer patients (Stage II-IV) planned with a two arcs VMAT technique. Prescription doses ranged from 50.4Gy to 66Gy in 1.8 or 2Gy per fraction, with one case of dose painting. Target volumes were generated per clinical standard of care. The ITVs ranged from 18cc-387cc. Using the clinically delivered isocenter and beam set-up, we retrospectively generated MCO plans with a universal set of constraints and objectives that was developed by trying different combinations in a few patients. Two versions of the MCO plan scores (one navigated by the dosimetrist [MCOd] and one by the physician [MCOp]) were compared with clinical plans generated with Direct Machine Parameter Optimization (DMPO). Dosimetric and biological parameters evaluated were PTV V95%, Conformity Index (CI), PTV Dmax and the un-complicated probability (UP) representing the absence of lung and esophagus complications. The cord dose was not evaluated because almost all plans had Dmax doses of less than 45Gy, with negligible probability of complications. MCOd vs clinical comparison: the values for PTV V95 were MCOd: 99%(95-100) vs clinical plans: 98% (94-100),p-value= 0.2, the CI were similar in both cases (p-value=0.5) but the Dmax was higher for the MCO plans (average 109% vs. 107%, p =0.004), the lung-esophagus UP was similar between MCOd (Mean: 74%, range: 55-87%) and the clinical pla(Mean:75%, range: 60-89%), p= 0.1. Corresponding MCOd versus MCOp comparisons were similar for the parameters tested. However, using real time assessment of dosimetric trade-offs, in each individual plan the physician was able to actively choose a preferred combination of dose to target vs organs. When evaluating individual patients, there were five patients for which MCO plans had a clear advantage in reducing dose to lung and/or esophagus while improving/maintaining target coverage, four patients with comparable plans and one patient where MCO was worse. MCO VMAT lung plans obtained with standardized objectives and constraints generated comparable or better plans than the clinical DMPO plans while allowing physicians to make real time comparisons of dosimetric trade-offs and accept a plan optimal for an individual patient.