Compensator-based IMRT for malignant pleural mesothelioma post extrapleural pneumonectomy

Abstract

Abstract:  The purpose of this study was to investigate Compensator-Based Intensity Modulated Radiation Therapy (CB-IMRT) as an alternative to MLC based IMRT for large field IMRT. We investigated the potential of this modality to treat malignant pleural mesothelioma (MPM) post Extra Pleural Pneumonectomy (EPP). Materials and Methods: A commercial treatment planning system XIO/CMS (Computerized Medical Systems, Inc., 1195 Corporate Lake Drive, St Louis, MO 63132) was used to generate plans for four right-sided and one left-sided MPM cases. These plans utilized seven gantry angles with a total of 11 coplanar 6 MV fields. The maximum required field size was 30x40 cm². IMRT plans with .decimal brass compensators (. decimal121 central park place, Sanford, FL 32771) were evaluated by examining  isodose distributions, dose-volume histograms (DVHs), and other metrics to quantify conformal plan quality and homogeneity. Extensive quality assurance was performed for one of the compensator plans. Results: Conformal dose distributions were achieved for all five cases with compensators where the average PTV coverage was 95.1% of PTV volume receiving the full prescription dose of 45 Gy. The average lung V20, (Volume Of lung receiving 20 Gy) was 1.8 %, Mean Lung Dose (MLD) was 6.7 Gy the average contra lateral kidney V15 was 0.6%.  The average liver dose V30 was 34.0% for the right sided cases and 10% for the left sided case. The average number of monitor units (MUs) required per fraction was 980 MU. Conclusions: Compensator plans showed acceptably conformal dose distributions confirmed by multiple measurement techniques. Not all linear accelerators can deliver large field MLC based IMRT, but most can deliver a maximum conformal field of 40x40 cm².  It is possible and reasonable to deliver IMRT with compensators for fields this size with most conventional linear accelerators which makes CB-IMRT an attractive alternative.