Background: In external radiation therapy, the percentage depth dose (PDD) is an important factor for estimating patient dose and dose distribution in target volume; therefore, its exact measurement or calculation is important. The aim of this study was to evaluate analytically the dose received by different points in water phantom and to compare it with dosimetry measurement data.Methods: To find the dose distribution throughout the tumor volume, first, the mathematical approach was performed for derivation of percentage depth dose photon beams of 6MV and 18MV Varian accelerator. Second, by dosimetry for different fields in different depths of water phantom, one can parameterize the obtained formula for percentage depth dose.Results: By comparing the mathematical and dosimetry results, the parameters of PDD-expression were computed in terms of the dimension of equivalent square field in different depths. From this formula, one can find the PDD for any fields in different depths, surface skin dose, and depth of build-up region of dose distribution, which are in agreement with empirical results with R2 >0.995, showing a good agreement with the experimental data.Conclusion: So one can measure the surface skin-dose, the depth of build-up region, and their variations in terms of square field size exactly; the measurement of these quantities have some technical problems in radiation dosimetry.

Background: Radiation-sensitive polymer gels are among the most promising three-dimensional dose verification tools and tissue-like phantom developed to date.Objective: The aim of this study is an investigating of percentage depth dose enhancement within the gel medium with used of conformal distribution gold nanoparticle as contrast agents by high atomic number material.Methods: In this work the normoxic polymer gel dosimeter MAGICA tissue-equivalence was first theoretically verified using MCNPX Monte Carlo code and experimentally by percentage depth dose curves within the gel medium. Then gold nanoparticles (GNPs) of 50nm diameter with different concentrations of 0.1mM, 0.2mM, and 0.4mM were embedded in MAGICA gel and irradiated by 18MV photon beam.Results: Experimental results have shown dose increase of 10%, 2% and 4% in 0.1mM, 0.2mM and 0.4mM concentrations, respectively. Simulation results had good agreement in the optimum concentration of 0.1mM. The largest error between experimental and simulation results was equal to 9.28% stood for 0.4mM concentration.Conclusion: The results showed that the optimum concentration of gold nanoparticles to achieve maximum absorbed dose in both experimental and simulation was 0.1 mM and so it can be used for clinical studies.

Background: In radiotherapy, low-energy photon beams are better adapted to the treated volume, and the use of high-energy beams can reduce hot spots in the radiation therapy. Therefore, mixing low and high energies with different ratios can control the rate of hotspots, as well as the dose distribution of the target volume. Material and Methods: The percentage depth doses (PDDs) were calculated at various depths, by using a fitted double exponential equation. Then, using quality factor equation and PDD of a 10×10 cm2 field, the amount of energy equivalent to each PDD and the value of weighting factors of 6, 18 MV energies were calculated to produce different energies. To validate the mathematical model, dosimetry of 10 MV energy was used. For this purpose, PDDs and dose Profile of 10 MV obtained from the mix were compared with ones obtained from the measurement Results: The value of weighting factor of 6 MV energy required for the 10 ×10 cm2 field to create dose distribution of 15 MV energy using 6 and 18 MV energies was obtained as equal to 0. 57. Comparison of percentage depth dose curves and dose profile shows good agreement with the practical measurements of 10 MV for 10×10 cm2 field using gamma index. Conclusion: The simultaneous use of high and low photon energies with different weighting factors to achieve desirable energy makes possible the treatment of tumors located at various depths without the need for different modes of energy in the accelerator leading to a decrease in the cost of the equipment and a safer treatment of the cancerous patients.

INTRODUCTION: Radiotherapy treatment for patients who have undergone breast saving operation is basically tangential radiation using cobalt or other high-energy photons. Electron beam therapy is the method of choice for patients undergoing modified radical "mastectomy (MRM). Rapid fall off of the percentage depth dose (DD%), homogeneous dose distribution and limited dose to the sub-tumoral tissues are the outstanding features of electron therapy. Chest wall and axillary regions should be treated with electron beams in MRM. The treatment field includes chest wall, axillary, sub- and supra-clavicular lymph nodes and internal mammary nodes. The aim of this work was to study the depth dose of 10 and 13 MeV electron beams in the chest wall, lymph nodes and lungs when the chest wall was radiated anteriorly. METIIODS: In this study two high-energy linear accelerators (Neptune 10 and Saturn 20) were used as the sources of electron beams. Measurements of the DD% were performed in a Perspex phantom using TLD (TLD-100) dosimetry method. The phantom was designed based on the chest wall CT images of mastectomized patients. RESULTS: The measured DD% to the internal mammary nodes, axillary nodes and chest wall were 97.5%, 96% and 98%, respectively, when the electron energy was 13 MeV, and they were 90.5%, 77% and 99.7%, respectively, when 10 MeV electrons beams were used. The anterior lung parenchymal DD% was 78% with 13 MeV electron beams, while the posterior part of the lung received 47% of the maximum dose. With 10 MeV electron beams, the values for anterior and posterior parts of the lung were 83% and 45%, respectively. DISCUSSION: Using 13 MeV electron beams, internal mammary and axillary lymph nodes and the chest wall received adequate doses, while the lungs were excessively exposed to radiation. With 10 MeV electron radiation therapy, internal mammary nodes "and chest wall were well exposed to radiation, yet axillary nodes did not receive enough radiation. Hence, axillary lymph nodes should receive additional radiation from the posterior field.

Introduction: The aim is to observe that the measurement of tissue maximum ratio (TMR) by water phantom directly differs from the calculation of TMR from percentage depth dose (PDD) or not. Material and Methods: The linear accelerator Siemens (6 MV & 10MV) with 82 leaves (MLC)-based stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT). The water phantom (PTW) was used for measuring the dosimetric parameter of TMR &%DD. This data was calculated using 0. 125 cc simeflex ionization chamber. The small fields have different sizes ranging from 12. 50 to 40. 00 mm in diameter. Results: There were small observations of mean error ≤,1. 50 % for all collecting data related to depths and field sizes. The Statistical Package of Social Science (SPSS) (version 26) to generate results. Wilcoxon Signed Ranks Test was used to compare two groups,(p ≤,0. 05) was considered significant. There were no significant differences between TMR data. The measured TMR data calculated from %DD had a strong positive correlation for cone sizes from 1. 0 cm x1. 0 cm to 10. 0 cm x10. 0cm. Conclusion: It has been shown that the calculation of TMR data from PDD agrees with the measuring values directly, and it is accepted for use in treatment.

Background: External beam radiation therapy is often administered to patients implanted with silicone gel breast prosthesis. The aim of this study was to investigate the influence of silicone gel breast prosthesis on photon dose distributions. In the event of recurrence, the oncologist may be forced to irradiate through the prosthetic device. To quantify the dose enhancement or reduction below the silicone gel breast prosthesis, depth dose enhancement factors (DEFs) were calculated. Materials and Methods: The study was based on Varian linear accelerator (LINAC) operated at 6 and 15 MV photon energies. Monte Carlo package Electron Gamma Shower (EGSnrc) was employed to simulate the depth dose distribution in a three dimensional scanning water phantom with various field sizes. The polydimethyl silicone gel breast prosthesis with density of 0. 97 g/cm3 was used. The measured and calculated DEFs were verified by using the thermoluminescent dosimeter (TLD). Results: The results indicate that the percentage difference between the calculated and measured dose distributions on depth dose curves for 6 and 15 photon energies was less the 2% for all locations. DEFs at 0. 5 cm below the 3. 5 cm prosthesis were 0. 99 and 1. 02 for 6 and 15 MV photon beams, respectively. The interface region receives enhanced dose of about 2. 4% with 15 MV photon beam while the 6 MV photon beam delivered a dose reduction of about 2. 0%. Conclusion: It was observed that DEFs increase with photon beam energy. The 6 MV photon beam reduces dose enhancement factor compared to that of the 15 MV photon beam.