VOLUMETRIC MODULATION ARC RADIOTHERAPY COMPARED WITH STATIC GANTRY INTENSITY-MODULATED RADIOTHERAPY FOR MALIGNANT PLEURAL MESOTHELIOMA TUMOR: A FEASIBILITY STUDY

Purpose: A planning study was performed to evaluate RapidArc (RA), a volumetric modulated arc technique, onmalignant pleural mesothelioma. The benchmark was conventional fixed-field intensity-modulated radiotherapy(IMRT).Methods and materials: The computed tomography data sets of 6 patients were included. The plans for IMRTwithnine fixed beams were compared against double-modulated arcs with a single isocenter. All plans were optimizedfor 15-MV photon beams. The dose prescription was 54 Gy to the planning target volume. The planning objectivesfor the planning target volume were a minimal dose of >95% and maximal dose of <107%. For the organs at risk,the parameters were as follows: contralateral lung, percentage of volume receiving 5 Gy (V5Gy) <60%, V20Gy< 10%, mean <10.0 Gy; liver, V30Gy <33%, mean <31 Gy; heart, V45Gy <30%, V50Gy <20%, dose received by1% of the volume (D1%) <60 Gy; contralateral kidney, V15Gy <20%; spine, D1% <45 Gy; esophagus, V55Gy<30%; and spleen, V40Gy <50%. The monitor units (MUs) and delivery time were scored to measure the treatmentefficiency. The pretreatment portal dosimetry scored delivery to the calculation agreement with the GammaAgreement Index.Results: RA and IMRT provided equivalent coverage and homogeneity. Both techniques fulfilled objectives on organsat risk with a tendency of RA to improve sparing. The conformity index was 1.9 ± 0.1 for RA and IMRT. Thenumber of MU/2Gy was 734 ± 82 for RA and 2,195 ± 317 for IMRT. The planning vs. delivery agreement revealeda Gamma Agreement Index for IMRTof 96.0% ± 2.6% and for RA of 95.7% ± 1.5%. The treatment time was 3.7 ±0.3min for RA and 13.4 ± 0.1min for IMRT.Conclusion: RA demonstrated compared with conventional IMRT, similar target coverage and better dose sparingto the organs at risks. The number of MUs and the time required to deliver a 2-Gy fraction were much lower forRA, allowing the possibility to incorporate this technique in the treatment options for mesothelioma patients.