الفهرس 
Abstract
Apparatus and measuring instrumentsOnly 14 pages are availabe for public view
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Abstract
The study aimed to investigate the performance of lithium fluoride thermoluminesent dosimeters (TLD-700) to photon beams applied in clinical radiology in energy range 75 kV to 15 MV at variable dose ranges. The study extended to evaluate the implication of sorting multiple crystals per reading on its response. The PDD and off axis were measured in energy range 75 kV to 15 MV. Entrance surface dose (ESD) was measured, in and out the selected field, for some applications used in clinical radiology. A comparison between measured and calculated dose were made for the treatment planning of the brain on 60Co and 6MV Linac. x-ray. TLD-700 employed in this study were selected in such a way that their sensitivity did not differ by more than ± 5% of the average. The selected crystals exhibits good homogeneity with relative sensitivity ranged 0.99-1.00 and acceptable stability ranged 3.36-4.42% over 5 reuse cycles of irradiation and measurements at Co-60 γ–rays. No significant variations (P>0.05) were found in TLD responses at photon energy ranging 75 KVp to 15 MV. The TLDs showed good linearity over dose range 0.2-4 cGy at 75 KVp and 1-1100 cGy for Co-60 γ–ray, 6 and 15 MV x-rays. The results of measuring multiple crystals per TL-reading showed good linearity of TLD response with the number of sorted crystals ranged 1-8 crystals. No significant difference exists in TLD sensitivity of individual and three sorted crystals over energy range employed in this study. The PDD and off-axis were measured for photon energy ranging 75 kV to 15 MV. PDD for the megavoltage machines the data compared with the published data, ionization chamber (0.6cc), and TPS, for 60Co, 6, and 15 MV photon beams. The data shows small difference between the data measured by the TLD-700, and the other data. The depth dose curves are similar in the general shape. The peripheral doses (PD) at different points around the irradiated field in energy range 75 kV to 15 MV was measured. For kilovoltage energy the dose at 5 cm from the edge of the field the dose falls down to 70% from its value. At distance more than 20 cm, for plain diagnostic or RT-simulator fields from the edge of field, the points received insignificant values. For megavoltage energy at 5 cm from the edge of the field, the relative dose ranged from 10.78 % to 23.42 % for different field size, it is also observed that at distance more than 60 cm for megavoltage radiation field, from the edge of field, the points received insignificant values, but at distances less than 5 cm from edge field should keep in mined especially it can found sensitive organ in this region. A comparison between measured and calculated dose was made for two megavoltage energies, 60Co and 6MV X-ray. Measurements of dose distributions for the isocentric brain during three field treatments indicated that the errors are limited to the errors arising from the measurements using the TLD-700 chips and doesn’t exceeds the standard limits.