Are there any dosimetric advantages in using VMAT for treatment of locally advanced non-small cell lung cancer?

Purpose. - To analyse the dosimetric differences between the conventional conformal radiation therapy (CR) and the volumetric modulated arc therapy (VMAT) for non-small-cell locally advanced lung cancer (NSCLC). Patients and methods. - Two plans (CR and VMAT) were calculated for ten NSCLC patients. Dose to PTV, organs at risk and external contours (body), conformity index (PTV volume/volume of the 95% reference isodose) and homogeneity index ([maximal dose - minimal dose]/dose prescription) were compared. Results. - Doses delivered to PTV (homogeneity index, maximal, minimal and mean dose) are similar with both techniques but conformity index is improved by 60% with VMAT: from 0.55 +/- 0.07 with CR to 0.89 +/- 0.07 with VMAT (P = 0.002). Pulmonary protection is improved with VMAT: with CR and VMAT, respectively, the mean lung dose is 14.1 +/- 5.2 Gy and 12.2 +/- 4.5 Gy, the lung volume which receives at least 30 Gy (V30) is 20 +/- 8% and 14 +/- 5%, and the V20 is 24 +/- 11% and 20 +/- 10% (P = 0.002). The mean dose received by the body is also 9% lower (P = 0.004) and V5 is 13% higher (P = 0.004) with VMAT. V10 and V15 were similar with both modalities. From 20 Gy and higher, irradiated body volume is larger with CR than with VMAT. The relative difference increases with the dose: from 10% for 20 Gy (P = 0.014) up to 39% for 62.7 Gy (P = 0.002). Conclusion. - Compared to CR, VMAT greatly improves conformity and reduces mean dose and dose delivered from 20 Gy and higher to the lungs and the body. (c) 2012 Societe francaise de radiotherapie oncologique (SFRO). Published by Elsevier Masson SAS. All rights reserved.