Influences of various field-defining methods of Varian accelerator on radiation dosimetry parameters / 中华放射医学与防护杂志

ABSTRACT

Objective To evaluate the influences of various field-defining method of Varian accelerator on radiation dosimetry parameters, and provide theoretical basis for the beam modeling of the treatment planning system ( TPS ) . Methods The percentage depth dose ( PDD ) , the off-axis ratio ( OAR ) and the total scattering factors ( Scp ) of radiation fields were measured in three different conditions, including collimators (JAW), multileaf collimator(MLC) and JAW +MLC. The measured data was analyzed and compared with each other. Results The PDD of central axis was marginally influenced by three field-defining method. In both directions, the MLC-defined field sizes were larger by a maximum of 2. 9 mm ( left-right) or 1. 7 mm ( gun-target) than the JAW-defined ones. In the left-right direction, the width of field penumbra shaped by MLC was larger than the field of the same size as defined by JAW. The result of gun-target direction was to the contrary. In both directions, the field penumbra and size displayed no significant differences as defined by JAW+MLC or JAW. Conclusions The field size, penumbra width, and the total scattering factors were influenced by field-defining method, which indicates that special attention should be paid to the dosimetric parameters of MLC during TPS beam modeling for IMRT planning.