Fabrication Of A Reuseable Plastic Based X-Ray Dosimeter For Radiotherapy
| dc.contributor.author | Iqbal, Tariq | |
| dc.date.accessioned | 2017-09-08T00:51:05Z | |
| dc.date.available | 2017-09-08T00:51:05Z | |
| dc.date.issued | 2016-01 | |
| dc.description.abstract | The aim of this study was to fabricate a plastic composite dosimeter for the measurement of radiation doses of X -ray photons used in radiotherapy. The criteria for the proposed dosimeter were low cost, ease of use, non toxic, and reusable. As a dosimeter, it should have acceptable sensitivity and reliability in the dose measurements range of interest in radiotherapy. In making plastics based dosimeters, radiation sensitive material grains were uniformly embedded in transparent plastic host where they are kept spatially fixed. Changes in optical transmission spectra of the materials was used as readout method, using Shimadzu UV 1800 spectrophotometer. These changes were than calibrated to get the absorbed doses. Optical bleaching of the irradiated samples were performed with two 100 watts ordinary bulbs for 18 hours. Among the thirteen materials that were selected for the study of their suitability as the embedding material, research grade pure sodium chloride was found to be the most suitable material. Other materials studied were beryllium oxide, seven different types of edible salts available in local markets, un doped aluminium oxide, potash alum (tawas), ammonium chloride (Noshadar) and bamboo salt. PMMA (polymethyl metaacrylate) was chosen as the host material. The final plastic sample was produced using Haake poly drive internal mixer and hot press machine, as 2 mm thick plastic sheet, with uniformly embedded grounded (125μm) pure sodium chloride grains in 40/60 sodium chloride to PMMA wt/wt ratio. All the evaluations of embedding materials were carried out with their samples placed inside a transparent plastic vial containing optically clear oil. This plastic vial was found to have optical properties very close to the final, material free, PMMA sample. It was observed that treatment of samples using 9 MeV electron doses of up to 2800 Gy does not changed their sensitivity. The aforementioned final plastic sample, containing sodium chloride labelled as N1, have shown response to 6 MV photons with a linear dose response from 3 Gy to10 Gy. The sensitivity appeared to be decreased between 10 Gy to15 Gy, after which appeared to recover for the last observed dose of 20 Gy. The decrease in 15 Gy response is postulated to be due to the depletion of the trapped electrons of interest, supposed to produce optical absorption at 395 to 550nm, due to fluorescence up-conversion resulting from 570 to 625 nm absorption during measurements. The Zeff of the PMMA plastic based dosimeter containing 40% N1 by weight was calculated to be 10.51 a.m.u. The N1 samples irradiated with 5 Gy 6MV photons has shown fading of 16.92% and 48.06% for one week and one month respectively. The dose reproducibility was estimated with the average response of three fresh samples to 5 Gy 6 MV photons. The doses were delivered for alternate 4 days post optical bleaching of 18 hours. The area of dip in the percentage transmission curve corresponding the absorbed dose was found to have an average value of 96.4 arbitrary area units with standard deviation of 4.85%. The peak values of the dips were found to be between 460 nm to 472 nm. The fabricated plastic based dosimeter was found to be robust, cheap, easy to use and reusable and suitable for measuring doses of X-ray photons, in the dose ranges of linear responses, 3 Gy to10 Gy and for observed higher doses, 15 Gy and 20 Gy. | en_US |
| dc.identifier.uri | http://hdl.handle.net/123456789/4529 | |
| dc.language.iso | en | en_US |
| dc.publisher | Universiti Sains Malaysia | en_US |
| dc.subject | Plastic Based X-Ray Dosimeter | en_US |
| dc.subject | For Radiotherapy. | en_US |
| dc.title | Fabrication Of A Reuseable Plastic Based X-Ray Dosimeter For Radiotherapy | en_US |
| dc.type | Thesis | en_US |
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