No abstract

Natural fibers are potentially a high-performance and non-abrasive reinforcing fiber source. In this study, mechanical properties of polypropylene (PP) composites with various natural fibers such as old newsprint, kraft pulp and hemp were studied. The effect of a low-molecular weight, maleated type coupling agent, on the mechanical properties of these natural fiber-filled PP composites was also investigated and the results showed that this can be used as a good interface modifier for improving the strength properties of the PP-filled composites and the optimum level of the coupling agent was found to be around 3-4 percentage by weight of the composite. Kraft pulp and hemp fiber-filled composites showed better tensile, flexural and un-notched impact strength compared to the glass fiber-filled composites at the same fiber loading. Hybrid composite produced using 10 wt% of glass fiber and 30 wt% of hemp fiber showed only a marginal improvement in the mechanical properties.

In vivo dose verification in brachytherapy requires a small insertable dosimeter with a real-time readout capability. Fibre optic scintillation dosimeters, consisting of a plastic scintillator coupled to an optical fibre, are one of the most promising dosimeters for this application. We have developed two sizes of the BrachyFOD TM scintillation dosimeter which have external diameters of 2.2 mm and 1 mm and have determined their important dosimetric characteristics (depth dose relation, angular dependence, temperature dependence, energy dependence). We have shown that the background signal created by Cerenkov and fibre fluorescence does not significantly affect the performance in most clinical geometries using an 192 Ir source from an HDR brachytherapy unit. The dosimeter design enables readout at less than 0.5 s intervals. The BrachyFOD TM satisfies the need for a real-time in vivo brachytherapy dosimeter.

The large dose gradients in brachytherapy necessitate a detector with a small active volume for accurate dosimetry. The dosimetric performance of a novel scintillation detector (BrachyFOD) is evaluated and compared to three commercially available detectors, a diamond detector, a MOSFET, and LiF TLDs. An 192Ir HDR brachytherapy source is used to measure the depth dependence, angular dependence, and temperature dependence of the detectors. Of the commercially available detectors, the diamond detector was found to be the most accurate, but has a large physical size. The TLDs cannot provide real time readings and have depth dependent sensitivity. The MOSFET used in this study was accurate to within 5% for distances of 20 to 50 mm from the 192Ir source in water but gave errors of 30%-40% for distances greater than 50 mm from the source. The BrachyFOD was found to be accurate to within 3% for distances of 10 to 100 mm from an HDR 192Ir brachytherapy source in water. It has an angular dependence of less than 2% and the background signal created by Cerenkov radiation and fluorescence of the plastic optical fiber is insignificant compared to the signal generated in the scintillator. Of the four detectors compared in this study the BrachyFOD has the most favorable combination of characteristics for dosimetry in HDR brachytherapy.