38 research outputs found
Estimating the Effect of Student Aid on College Enrollment: Evidence from a Government Grant Policy Reform
NMR spectroscopy of saccharide-doped PAGAT dosimeters
he aim of this study was to investigate the chemistry of the PAGAT dosimeters when doped with saccharides and irradiated\u27 using NMR spectroscopy. Three batches of PAGAT gel dosimeters were manufactured. Two of them were doped with 20 % glucose and sucrose\u27 respectively. For each batch\u27 one sample was left unirradiated while the remaining samples were irradiated to different doses. After irradiation\u27 NMR spectra were obtained which clearly showed the composition of the dosimeter and the change in monomer concentration caused by irradiation. In addition\u27 it revealed that the saccharides did not directly participate in the chemical process before and during irradiation but the addition of saccharides resulted in a higher consumption rate of the monomers
Feasibility study using MRI and two optical CT scanners for readout of polymer gel and Presage (TM)
The aim of this study was to compare the conventional combination of three-dimensional dosimeter (nPAG gel) and readout method (MRI) with other combinations of three-dimensional dosimeters (nPAG gel/Presage (TM)) and readout methods (optical CT scanners). In the first experiment, the dose readout of a gel irradiated with a four field-box technique was performed with both an Octopus IQ scanner and MRI. It was seen that the MRI readout agreed slightly better to the TPS. In another experiment, a gel and a Presage (TM) sample were irradiated with a VMAT field and read out using MRI and a fast laser scanner, respectively. A comparison between the TPS and the volumes revealed that the MRI/gel readout had closer resemblance to the TPS than the optical CT/Presage (TM) readout. There are clearly potential in the evaluated optical CT scanners, but more time has to be invested in the particular scanning scenario than was possible in this study
Do saccharide doped PAGAT dosimeters increase accuracy?
To improve the dosimetric accuracy of normoxic polyacrylamide gelatin (PAGAT) gel dosimeters, the addition of saccharides (glucose and sucrose) has been suggested. An increase in Râ‚‚-response sensitivity upon irradiation will result in smaller uncertainties in the derived dose if all other uncertainties are conserved. However, temperature variations during the magnetic resonance scanning of polymer gels result in one of the highest contributions to dosimetric uncertainties. The purpose of this project was to study the dose sensitivity against the temperature sensitivity. The overall dose uncertainty of PAGAT gel dosimeters with different concentrations of saccharides (0, 10 and 20%) was investigated. For high concentrations of glucose or sucrose, a clear improvement of the dose sensitivity was observed. For doses up to 6 Gy, the overall dose uncertainty was reduced up to 0.3 Gy for all saccharide loaded gels compared to PAGAT gel. Higher concentrations of glucose and sucrose deteriorate the accuracy of PAGAT dosimeters for doses above 9 Gy.4 page(s
Evaluation of radiochromic gel dosimetry and polymer gel dosimetry in a clinical dose verification
Considerations for study design in the DAHANCA 35 trial of protons versus photons for head and neck cancer
Proton radiotherapy offers a dosimetric advantage compared to photon therapy in sparing normal tissue, but the clinical evidence for toxicity reductions in the treatment of head and neck cancer is limited. The Danish Head and Neck Cancer Group (DAHANCA) has initiated the DAHANCA 35 randomised trial to clarify the value of proton therapy (NCT04607694). The DAHANCA 35 trial is performed in an enriched population of patients selected by an anticipated benefit of proton therapy to reduce the risk of late dysphagia or xerostomia based on normal tissue complication probability (NTCP) modelling. We present our considerations on the trial design and a test of the selection procedure conducted before initiating the randomised study.</p
Copy number variation of scavenger-receptor cysteine-rich domains within DMBT1 and Crohn’s disease
Previous work has shown that the gene DMBT1, which encodes a large secreted epithelial glycoprotein known as salivary agglutinin, gp340, hensin or muclin, is an innate immune defence protein that binds bacteria. A deletion variant of DMBT1 has been previously associated with Crohn’s disease, and a DMBT1−/− knockout mouse has increased levels of colitis induced by dextran sulphate. DMBT1 has a complex copy number variable structure, with two, independent, rapidly mutating copy number variable regions, called CNV1 and CNV2. Because the copy number variable regions are predicted to affect the number of bacteria-binding domains, different alleles may alter host–microbe interactions in the gut. Our aim was to investigate the role of this complex variation in susceptibility to Crohn’s disease by assessing the previously reported association. We analysed the association of both copy number variable regions with presence of Crohn’s disease, and its severity, on three case–control cohorts. We also reanalysed array comparative genomic hybridisation data (aCGH) from a large case–control cohort study for both copy number variable regions. We found no association with a linear increase in copy number, nor when the CNV1 is regarded as presence or absence of a deletion allele. Taken together, we show that the DMBT1 CNV does not affect susceptibility to Crohn’s disease, at least in Northern Europeans