Monte Carlo simulation and dosimetric verification of physical wedges used in radiation therapy

The presence of a wedge filter in the beam trajectory can modify the beam quality and cause some changes in the dosimetry parameters which are usually difficult to be measured directly and accurately. In this study the MCNP-4C Monte Carlo code was used to simulate the 9 MV photon beam generated by a linear accelerator. Upon getting a good agreement between the Monte Carlo simulated and measured dose distribution in open fields, the model was used to simulate the physical wedges. The steel wedges with angles from 15°-60° were modeled and the primary and the secondary photon beams were calculated. The beam profiles and wedges factors were calculated for each wedge. The output factors were determined for 45 wedge. The calculated data were compared with the measured values of the same parameters. The results showed that the use of wedges reduced the fluencies of the primary and scattered photons and also increased the average energy of the primary and the scattered photons. The agreement between the calculated and the measured data was better than 2% for all wedges. The results also showed that as the wedge angle increased, the electron contamination of photon beam decreased. The presence of a wedge in a 9 MV photon beam alters the primary and the scattered components generated by a linear accelerator. The simulated linac machine and its associated data can be used to predict the dose distribution in other complex fields

Application of dose-area product compared with three other dosimetric quantities used to estimate patient effective dose in diagnostic radiology

Application of dose-area product [DAP] quantity has been increased in the clinical practice. DAP is relatively easy to measure, and has been shown to correlate well with the total energy to the effective dose imparted to the patient correlated. Measurements of DAP were carried out with 421 adult patients who underwent conventional radiological examinations. Then, some useful dosimetric quantities such as exposure area product [EAP], air kerma and entrance surface dose [ESD] were estimated. Furthermore, effective doses were computed by the measurement of DAP and corresponding conversion factors. The effective dose values derived from various methods are in good agreement. The mean effective dose estimated from DAP measurements were 0.13, 0.42, 0.05, 0.59, 0.54 and 0.03 mSv/projection for chest, abdomen, cervical spine, lumbar spine, pelvis and skull examinations, respectively. Indirect effective dose determination using the NRPB dosimetric data and the measured value of DAP or ESD allows for reliable estimates of effective dose. The ODS-60 software was used in this study as to it's flexibility to manipulate the technical parameters of an examination and patient's parameters