Gold nanoparticle and mean inactivation dose of human intestinal colon cancer HT-29 cells

Background: Mean inactivation dose is a useful radiobiological parameter for the comparison of human cell survival curves. Objectives: Given the importance and accuracy of these parameters, in the present study, the radio sensitivity enhancement of colon cancer (HT-29) cells in the presence of gold nanoparticles (GNPs) were studied using the mean inactivation dose (MID). Materials and Methods: Naked-GNPs with 50 nm diameters were incubated with HT-29 cells. The cytotoxicity and uptake of these particles on HT-29 cells were assessed. After determining the optimum GNPs concentration, the cells were incubated with gold nanoparticle for 24 hours. The change in the MID value as well as the radio sensitization enhancement under irradiation with 9 MV X-ray beams in the presence of GNPs were evaluated by multiple (3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium)MTS assay. Results: Cell survival in the presence of GNPs was more than 90% and the maximum uptake of GNPs was observed at 60 μM of gold nanoparticles. In contrast, in the presence of GNPs combined with radiation, cell survival and MID value significantly decreased, so that the radio sensitization enhancement was 1.4. Conclusions: Due to the significant reduction in the mean inactivation dose of colon cancer cells in the presence of gold nanoparticles, it seems that GNPs are suitable options to achieve a new approach in order to improve radiotherapy efficiency without increasing the prescribed radiation dose

Dosimetric characteristics of mercury and cerrobend blocks in megavoltage radiation therapy

In this study some dosimetric parameters of mercury was investigated and compared with cerrobend as a common beam attenuator material. Experimental dosimetry for different thicknesses of cerrobend and mercury was done at 6 and 18 MV photon beams. With augmentation of the attenuator thickness, dmax and beam quality index increased at 6 MV but at 18 MV, beam softening happened. The transmission values increased with field size increment and linear attenuation coefficient decreases slightly as the thickness of the attenuating filter increased. The attenuation ability of mercury was about 1.44 times more than cerrobend and it can be proposed as a beam modifier. © 2014, Akadémiai Kiadó, Budapest, Hungary

Effective point of measurement in cylindrical ion chamber for megavoltage photon beams

Introduction: For dose measurement in Megavoltage (MV) photon beams with ion chambers, the effect of volume occupied by the air cavity is not negligible. Therefore, the result of measurement should be corrected with a displacement perturbation correction factor (Pdis) or using an effective point of measurement (EPOM). The aim of this study is to calculate the EPOM for cylindrical ion chamber and to evaluate the fixed EPOM that was recommended by standard dosimetry protocols. Materials and Methods: Percent depth doses (PDDs) for 6 MV and 18 MV were measured with two types of chambers for different depths and field sizes. The EPOM was calculated using results obtained from measurement data for two types of chambers, comparison of the readings, and using dosimetry, mathematical, and statistical consideration. For displacement correction factor �r=0, �r= 0.6r and different �r, the minimum standard deviations ratio (SDRs) were calculated at several depths and field sizes. Results: Maximum level of SDRs was about 0.38 and 0.49 (when assuming variable �r) for 6 MV and 18 MV, respectively (which was less than 0.5 and acceptable). This quantity was greater than one (for assuming �r= 0.6r) and greater than 2 when there was no shift (�r =0) Conclusion: The results show that the recommended shift for cylindrical ion chamber in dosimetry protocols (upstream of 0.6r) is not correct and using a fixed value for the EPOM at all photon beam energies, depths, and field sizes is not suitable for accurate dosimetry