Are Whole And Electronic Portal Imaging System Imrt

Intensity-modulated radiotherapy (IMRT) is capable of producing highly conformal dose distribution to a target through modulating intensity distribution of the beams irradiating the target. This capability makes it possible to give a high dose to the target volume while sparing adjacent normal tissues. This study investigates the influence of flattening filter on the IMRT treatment delivery time and the application of electronic portal imaging device (EPID) in dosimetric verification.The flattening filter in the treatment head is used to provide large, uniform x-ray fields for conventional radiotherapy. As for IMRT, the required fluence distributions are no longer needed to be uniform. Theoretically, without the flattening filter may reduce the treatment delivery time by enhancing the output dose rate. In the first part of this thesis, we investigate the overall effect of flattening filter on the treatment delivery time of IMRT with multileaf collimator (MLC) implemented in step and shoot method (SMLC), as well as with compensators on six hybrid machines for 20 patients. The results show that, without the flattening filter, the beam-on time reduces for both techniques. The number of segments and the leaf-travel time increase slightly for SMLC technique. The contribution of dose rate increase to reduction of treatment delivery time is relative small due to the influence of leaf-travel and V&R time. The treatment delivery time reduction also depends on the fraction dose. It is not clinically significant at fraction dose of 2 Gy for the technique of removing flattening filter, but becomes significant when the fraction dose is high.As an efficient dosimetric device, EPID has advantages in dosimetric verification. In the second part of this thesis, a backprojection dosimetry model is established and implemented through a C program to calculate the three dimension dosage distribution in the body by using the transmission...