Dosimetric verification of a commercial 3D treatment planning systemfor conformal radiotherapy with a dynamic multileaf collimator

Abstract

The dosimetric accuracy of a 3D treatment planning system (TPS)for conformal radiotherapy with a computer-assisted dynamic multileafcollimator (DMLC) was evaluated.The DMLC and the TPS have been developed for clinical applications wheredynamic fields not greater than 10×10 cm2 and multiplenon-coplanar arcs are required. Dosimetric verifications were performed bysimulating conformal treatments of irregularly shaped targets using severalarcs of irradiation with 6 MV x-rays and a spherical-shaped, tissue-simulatingphantom. The accuracy of the delivered dose at the isocentre was verifiedusing an ionization chamber placed in the centre of the phantom. Isodosedistributions in the axial and sagittal planes passing through the centre ofthe phantom were measured using double-layer radiochromic films. Measured doseat the isocentre as well as isodose distributions were compared to thosecalculated by the TPS. The maximum percentage difference between measured andprescribed dose was less than 2.5% for all the simulated treatment plans. Themean (±SD) displacement between measured and calculated isodoseswas, in the axial planes, 1.0±0.6 mm, 1.2±0.7 mm and1.5±1.1 mm for 80%, 50% and 20% isodose curves, respectively,whereas in the sagittal planes it was 2.0±1.2 mm and 2.2±2 mm for 80% and 50% isodose curves, respectively.The results indicate that the accuracy of the 3D treatment planning systemused with the DMLC is reasonably acceptable in clinical applications whichrequire treatments with several non-coplanar arcs and small dynamic fields.