Evaluation of dosimetric characteristics of a grid block fabricated for Mega-voltage grid therapy purposes

摘要

In conventional radiation therapy, regarding normal tissue tolerance, the treatment of bulk tumors is one of the remaining challenges. In order to cope with, Grid Radiation Therapy (GRT) is a technique to deliver high doses, approximately 15-20 Gy per fraction, to several small volumes located in a large radiation field. This can be performed using a grid block. The current work concentrates on the dosimetric characteristics of a designed mega-voltage grid, used for a unique treatment modality. A square 16x16 array grid block was designed and fabricated. Several dosimetric characteristics including: depth dose, Valley To Peak (VTP) ratio, and grid out-put factor were evaluated using a calibrated diode dosimeter for a range of radiation fields. The percent depth dose curves, measured in the presence of grid block, lie within those measured for the corresponding open field and a narrow beam. At the Dmax, the VTP ratio was fond to be within 17% - 28%, while these ranges between 23% - 35% at a depth of 10 cm. The grid output factor found to be 0.78 and it slightly decreases with increasing of radiation field size. The measured dosimetric characteristics of grid block indicate that the mega-voltage grid therapy can be applied as a possible clinical modality for palliative cases.