Radiation-sensitive polymer gels are among the most promising three-dimensional dose verification tools and tissue-like phantom developed to date. This study is an investigating of percentage depth dose enhancement wi...Radiation-sensitive polymer gels are among the most promising three-dimensional dose verification tools and tissue-like phantom developed to date. This study is an investigating of percentage depth dose enhancement within the gel medium with the use of conformal distribution gold nanoparticle as contrast agents by high atomic number material. 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 50 nm diameter with different concentrations of 0.1 mM, 0.2 mM, and 0.4 mM were embedded in MAGICA gel and irradiated by 18 MV photon beam. Experimental results have shown dose increase of 10%, 2% and 4% in 0.1 mM, 0.2 mM and 0.4 mM concentrations, respectively. Simulation results had good agreement in the optimum concentration of 0.1 mM. The largest error between experimental and simulation results was equal to 9.28% stood for 0.4 mM concentration. 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.展开更多
Small radiation fields are abundantly used in modern radiotherapy techniques like in IMRT and SRS. In order to commission these techniques, dosimetric data for small fields is required. The purpose of this study is to...Small radiation fields are abundantly used in modern radiotherapy techniques like in IMRT and SRS. In order to commission these techniques, dosimetric data for small fields is required. The purpose of this study is to compare dosimetric measurements with two different ion chambers cc13, and cc01 for smaller fields. Dosimetric measurements are beam profile, output factor, pdds, and collimator factor. Dosimetric data is acquired in water phantom for two different photon beam energies 6 MV and 15 MV with zero gantry angle. In beam profiles cc13 chamber, measure wider penumbra as compare to cc01. And this wider measurement of penumbra occurs for smaller as well as for larger field sizes. Accumulated relative error in the measurement of penumbra for number of field sizes and 6 MV at dmax, and at 10 cm depth are 34.32% and 27.72% respectively. Accumulated relative error in the measurement of penumbra for number of field sizes and 15 MV at dmax, and at 10 cm depth are 28.49% and 23.92%. In case of output factor for smaller fields cc13 underestimates the output factor relative to cc01, with non-linear increase for smaller fields. But for larger fields, this increase in output factor is almost linear difference of two chambers is decreased. For very smaller fields × 2 cm, relative error in output factor of cc13 and cc01 is greater than 5% and rapidly increases with decreasing field size. But for lager fields, this relative error is negligible. In measurement of pdds after the buildup region difference occurs in the response of two chambers cc13 and cc01 for smaller fields. For field sizes ≤2 cm × 2 cm average cc13-cc01 at various depths 30 cm, 40 cm, 50 cm, 60 cm, 70 cm, and 80 cm is almost greater than 0.5 cm. And similarly as output factor, this difference (cc13-cc01) increases with field size decreasing.展开更多
Thermoplastic immobilizing masks have dosimetric effects on the patient’s skin dose. The thermoplastic percentage depth dose (PDD), equivalent thickness of water for the masks and surface doses were determined. The s...Thermoplastic immobilizing masks have dosimetric effects on the patient’s skin dose. The thermoplastic percentage depth dose (PDD), equivalent thickness of water for the masks and surface doses were determined. The surface dose factors due to the thermoplastic mask was found to be 1.7949, 1.9456, 2.0563, 2.1967, 2.3827, 2.5459 and 2.6565 for field sizes of 5 × 5, 8 × 8, 10 × 10, 12 × 12, 15 × 15, 18 × 18 and 20 × 20 cm<sup>2</sup> respectively which shifted the percentage depth dose curve to lower values. The physical thermoplastic thickness was measured to be between 2.30 and 1.80 mm, and the equivalent thicknesses of water, d<sub>e</sub>, were determined to be between 1.2 and 1.00 mm. This meant that, as the mask thickness decreased, its water equivalent thickness also decreased. The presence of the mask material increased the skin dose to a factor of 1%. The thermoplastic mask factor was also found to be 0.99.展开更多
文摘Radiation-sensitive polymer gels are among the most promising three-dimensional dose verification tools and tissue-like phantom developed to date. This study is an investigating of percentage depth dose enhancement within the gel medium with the use of conformal distribution gold nanoparticle as contrast agents by high atomic number material. 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 50 nm diameter with different concentrations of 0.1 mM, 0.2 mM, and 0.4 mM were embedded in MAGICA gel and irradiated by 18 MV photon beam. Experimental results have shown dose increase of 10%, 2% and 4% in 0.1 mM, 0.2 mM and 0.4 mM concentrations, respectively. Simulation results had good agreement in the optimum concentration of 0.1 mM. The largest error between experimental and simulation results was equal to 9.28% stood for 0.4 mM concentration. 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.
文摘Small radiation fields are abundantly used in modern radiotherapy techniques like in IMRT and SRS. In order to commission these techniques, dosimetric data for small fields is required. The purpose of this study is to compare dosimetric measurements with two different ion chambers cc13, and cc01 for smaller fields. Dosimetric measurements are beam profile, output factor, pdds, and collimator factor. Dosimetric data is acquired in water phantom for two different photon beam energies 6 MV and 15 MV with zero gantry angle. In beam profiles cc13 chamber, measure wider penumbra as compare to cc01. And this wider measurement of penumbra occurs for smaller as well as for larger field sizes. Accumulated relative error in the measurement of penumbra for number of field sizes and 6 MV at dmax, and at 10 cm depth are 34.32% and 27.72% respectively. Accumulated relative error in the measurement of penumbra for number of field sizes and 15 MV at dmax, and at 10 cm depth are 28.49% and 23.92%. In case of output factor for smaller fields cc13 underestimates the output factor relative to cc01, with non-linear increase for smaller fields. But for larger fields, this increase in output factor is almost linear difference of two chambers is decreased. For very smaller fields × 2 cm, relative error in output factor of cc13 and cc01 is greater than 5% and rapidly increases with decreasing field size. But for lager fields, this relative error is negligible. In measurement of pdds after the buildup region difference occurs in the response of two chambers cc13 and cc01 for smaller fields. For field sizes ≤2 cm × 2 cm average cc13-cc01 at various depths 30 cm, 40 cm, 50 cm, 60 cm, 70 cm, and 80 cm is almost greater than 0.5 cm. And similarly as output factor, this difference (cc13-cc01) increases with field size decreasing.
文摘Thermoplastic immobilizing masks have dosimetric effects on the patient’s skin dose. The thermoplastic percentage depth dose (PDD), equivalent thickness of water for the masks and surface doses were determined. The surface dose factors due to the thermoplastic mask was found to be 1.7949, 1.9456, 2.0563, 2.1967, 2.3827, 2.5459 and 2.6565 for field sizes of 5 × 5, 8 × 8, 10 × 10, 12 × 12, 15 × 15, 18 × 18 and 20 × 20 cm<sup>2</sup> respectively which shifted the percentage depth dose curve to lower values. The physical thermoplastic thickness was measured to be between 2.30 and 1.80 mm, and the equivalent thicknesses of water, d<sub>e</sub>, were determined to be between 1.2 and 1.00 mm. This meant that, as the mask thickness decreased, its water equivalent thickness also decreased. The presence of the mask material increased the skin dose to a factor of 1%. The thermoplastic mask factor was also found to be 0.99.
