chromatographic analysis of pharmaceuticals

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Detection of therapeutic radiation in three-dimensions

For over the last twenty years there has been a multitude of sophisticated three-dimensional radiation delivery procedures developed which requires a corresponding verification of the impact on patients. This article reviews the state of the art in the development of chemical detectors used to characterize the three-dimensional shape of therapeutic radiation. These detectors are composed of polyurethane, radical initiator and a leuco dye, which is radiolytically oxidized to a dye absorbing at 630 nm

Water and tissue equivalence of a new PRESAGE® formulation for 3D proton beam dosimetry : a Monte Carlo study

Purpose: To evaluate the water and tissue equivalence of a new PRESAGE® 3D dosimeter for proton therapy. Methods: The GEANT4 software toolkit was used to calculate and compare total dose delivered by a proton beam with mean energy 62 MeV in a PRESAGE® dosimeter, water, and soft tissue. The dose delivered by primary protons and secondary particles was calculated. Depth-dose profiles and isodose contours of deposited energy were compared for the materials of interest. Results: The proton beam range was found to be ≈27 mm for PRESAGE®, 29.9 mm for soft tissue, and 30.5 mm for water. This can be attributed to the lower collisional stopping power of water compared to soft tissue and PRESAGE®. The difference between total dose delivered in PRESAGE® and total dose delivered in water or tissue is less than 2% across the entire water/tissue equivalent range of the proton beam. The largest difference between total dose in PRESAGE® and total dose in water is 1.4%, while for soft tissue it is 1.8%. In both cases, this occurs at the distal end of the beam. Nevertheless, the authors find that PRESAGE® dosimeter is overall more tissue-equivalent than water-equivalent before the Bragg peak. After the Bragg peak, the differences in the depth doses are found to be due to differences in primary proton energy deposition; PRESAGE® and soft tissue stop protons more rapidly than water. The dose delivered by secondary electrons in the PRESAGE® differs by less than 1% from that in soft tissue and water. The contribution of secondary particles to the total dose is less than 4% for electrons and ≈1% for protons in all the materials of interest. Conclusions: These results demonstrate that the new PRESAGE® formula may be considered both a tissue- and water-equivalent 3D dosimeter for a 62 MeV proton beam. The results further suggest that tissue-equivalent thickness may provide better dosimetric and geometric accuracy than water-equivalent thickness for 3D dosimetry of this proton beam.9 page(s

Water equivalence evaluation of PRESAGE® formulations for megavoltage electron beams : a Monte Carlo study

To investigate the radiological water equivalency of three different formulations of the radiochromic, polyurethane based dosimeter PRESAGE® for three dimensional (3D) dosimetry of electron beams. The EGSnrc/BEAMnrc Monte Carlo package was used to model 6-20 MeV electron beams and calculate the corresponding doses delivered in the three different PRESAGE® formulations and water. The depth of 50 % dose and practical range of electron beams were determined from the depth dose calculations and scaling factors were calculated for these electron beams. In the buildup region, a 1.0 % difference in dose was found for all PRESAGE® formulations relative to water for 6 and 9 MeV electron beams while the difference was negligible for the higher energy electron beams. Beyond the buildup region (at a depth range of 22-26 mm for the 6 MeV beam and 38 mm for the 9 MeV beam), the discrepancy from water was found to be 5.0 % for the PRESAGE® formulations with lower halogen content than the original formulation, which was found to have a discrepancy of up to 14 % relative to water. For a 16 MeV electron beam, the dose discrepancy from water increases and reaches about 7.0 % at 70 mm depth for the lower halogen content PRESAGE® formulations and 20 % at 66 mm depth for the original formulation. For the 20 MeV electron beam, the discrepancy drops to 6.0 % at 90 mm depth for the lower halogen content formulations and 18 % at 85 mm depth for the original formulation. For the lower halogen content PRESAGE®, the depth of 50 % dose and practical range of electrons differ from water by up to 3.0 %, while the range of differences from water is between 6.5 and 8.0 % for the original PRESAGE® formulation. The water equivalent depth scaling factor required for the original formulation of PRESAGE® was determined to be 1.07-1.08, which is larger than that determined for the lower halogen content formulations (1.03) over the entire beam energy range of electrons. All three of the PRESAGE® formulations studied require a depth scaling factor to convert depth in PRESAGE® to water equivalent depth for megavoltage electron beam dosimetry. Compared to the original PRESAGE® formulation, the lower halogen content formulations require a significantly smaller scaling factor and are thus recommended over the original PRESAGE® formulation for electron beam dosimetry.9 page(s

An investigation of the potential of optical computed tomography for imaging of synchrotron-generated x-rays at high spatial resolution

X-ray microbeam radiation therapy (MRT) is a novel form of treatment, currently in its preclinical stage, which uses microplanar x-ray beams from a synchrotron radiation source. It is important to perform accurate dosimetry on these microbeams, but, to date, there has been no accurate enough method available for making 3D dose measurements with isotropic, high spatial resolution to verify the results of Monte Carlo dose simulations. Here, we investigate the potential of optical computed tomography for satisfying these requirements. The construction of a simple optical CT microscopy (optical projection tomography) system from standard commercially available hardware is described. The measurement of optical densities in projection data is shown to be highly linear (r2=0.999). The depth-of-field (DOF) of the imaging system is calculated based on the previous literature and measured experimentally using a commercial DOF target. It is shown that high quality images can be acquired despite the evident lack of telecentricity and despite DOF of the system being much lower than the sample diameter. Possible reasons for this are discussed. Results are presented for a complex irradiation of a 22 mm diameter cylinder of the radiochromic polymer PRESAGE, demonstrating the exquisite 'dose-painting' abilities available in the MRT hutch of beamline ID-17 at the European Synchrotron Radiation Facility. Dose distributions in this initial experiment are equally well resolved on both an optical CT scan and a corresponding transmission image of radiochromic film, down to a line width of 83 microm (6 lp mm(-1)) with an MTF value of 0.40. A group of 33 microm wide lines was poorly resolved on both the optical CT and film images, and this is attributed to an incorrect exposure time calculation, leading to under-delivery of dose. Image artefacts in the optical CT scan are discussed. PRESAGE irradiated using the microbeam facility is proposed as a suitable material for producing phantom samples for quantitative characterization of optical CT microscopy systems

Treatment Plan 2—Gamma Maps.

<p>Three orthogonal views of 3%/3mm gamma maps for DFOS (column 2), DMOS (column 3), and DLOS (right) systems, with passing rates. Eclipse dose views (left) for reference.</p

Comparison of All Three Systems.

<p>Mean OD change (ΔOD) for the 4 distinct dose regions within the 4-field box treatment. The DFOS system is compared to the DLOS (blue) and DMOS (green). Also shown are linear fits for the two gold-standard systems compared to DFOS. Error bars span 2 standard deviations (95% confidence) for all systems.</p