There was no statistical significant difference in the rectal region between the two sets of scans in the 3D-CRT plans. The results showed that the dose differences between the plans for the CT scans with and without CM were small and clinically tolerable. However, the differences in the lower esophageal region were significant in the statistical analysis.

This study evaluated the basic dosimetric characteristics of a Dynamic Multi Leaf Collimator (DMLC) using a diode detector and film measurements for Intensity Modulated Radiation Therapy Quality Assurance (IMRT QA). The EGSnrc Monte Carlo (MC) simulation system was used for the determination of MLC characteristics. Radiation transmission and abutting leaf leakage relevant to the LinaTech DMLC H were measured using an EDGE detector and EBT3 film. In this study, the BEAMnrc simulation code was used for modeling. The head of Siemens PRIMUS linac (6 MV) with external DMLC H was entered into a BEAMnrc Monte Carlo model using practical dosimetry data. Leaf material density, as well as interleaf and abutting air gaps were determined according to the computed and measured dose profiles. The IMRT QA field was used to evaluate the dose distribution of the simulated DMLC H. According to measurements taken with the EDGE detector and film, the total average measured leakage was 1.60 ± 0.03% and 1.57 ± 0.05%, respectively. For these measurements, abutting leaf transmission was 54.35 ± 1.85% and 53.08 ± 2.05%, respectively. To adapt the simulated leaf dose profiles with measurements, leaf material density, interleaf and abutting air gaps were adjusted to 18 g/cm3, 0.008 cm and 0.108 cm, respectively. Thus, the total average leakage was estimated to be about 1.59 ± 0.02%. The step‐and‐shoot IMRT was implemented and 94% agreement was achieved between the film and MC, using 3%‐3 mm gamma criteria. The results of this study showed that the dosimetric characteristics of DMLC H satisfied international standards.

As regards, the selection of appropriate energy in radiotherapy tumors that are placed in non-homogen areas is important, so the aim of the present study is evaluating the effect of 6 and 15MV photon beam energies on dose distribution in 3D-CRT for lower esophageal and rectal cancers. 12 patients with lower esophageal cancer and 12 patients with rectal cancer respectively, with the prescription dose of 7000 cGy and 5040 cGy were studied. For treatment of esophagus the three-field technique and for treatment of rectum the four-field technique was used. In the thoracic area, the spinal cord and in the pelvis, the bladder and head of femurs were considered as OARs. For comparing the results, all parameters used for treatment planning except the photon beam energy were kept constant. After performing the treatment planning with two different energies in each region, the received dose rate of spinal cord, bladder and head of femurs as OARs and dose distribution in PTVs were studied. The results of this study showed that the difference between doses received by OARs in 6MV and 15MV therapeutic plans, resulted 5.2, 5.06 and -9.14%, respectively. Also the PTVs received dose difference of esophagus and rectum in the performed therapeutic plans with energy of 6 MV than energy of 15MV is 1.52 and -0.63%, respectively. We found that using of low energy photons in lower esophageal treatment and high energy photons in the rectal treatment provides the better dose coverage. Finally, with such as therapeutic plans the cumulative dose of organs at risk will be reduced.

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