AN INVESTIGATION OF THE EFFECT OF FORMALDEHYDE SPECIES ON ENVIRONMENTAL MEASUREMENT METHODS UNDER AMBIENT CONDITIONS

Species variations in formaldehyde solutions and gases were investigated by means of infrared spectral analysis. Double beam infrared spectrometry in conjunction with sodium chloride wafer technique and solvent compensation technique were employed. Formaldehyde species in various solutions were investigated. Formalin 37% was stable for many months. Refrigeration had no effects on its stability. Spectral changes were detected in 1000 ppm formaldehyde solutions. The absorbances of very diluted solutions up to 100 ppm were lower than the detection limit of the instruments. Solvent compensation improved resolution, but was associated with an observed lack of repeatability. Formaldehyde species in animal chambers containing animals and in mobile home air were analyzed with the infrared spectrophotometer equipped with a 10 cm gas cell. Spectra were not different from the spectrum of clean air. A portable single beam infrared spectrometer with a 20 meter pathlength was used for reinvestigation. Indoor formaldehyde could not be detected in the spectral; conversely, an absorption peak at 3.58 microns was found in the spectra of 3 and 15 ppm formaldehyde gas in animal chambers. This peak did not appear in the spectrum of the control chamber. Because of concerns over measurement bias among various analytical methods for formaldehyde, side-by-side comparisons were conducted in both laboratory and field measurements. The chromotropic acid method with water and 1% sodium bisulfite as collection media, the pararosaniline method, and a single beam infrared spectrometer were compared. Measurement bias was elucidated and the extent of the effects of temperature and humidity was also determined. The problems associated with related methods were discussed. ^

Verification of the clinical implementation of the respiratory gated beam delivery technique with synchrotron-based proton irradiation

The clinical advantage for protons over conventional high-energy x-rays stems from their unique depth-dose distribution, which delivers essentially no dose beyond the end of range. In order to achieve it, accurate localization of the tumor volume relative to the proton beam is necessary. For cases where the tumor moves with respiration, the resultant dose distribution is sensitive to such motion. One way to reduce uncertainty caused by respiratory motion is to use gated beam delivery. The main goal of this dissertation is to evaluate the respiratory gating technique in both passive scattering and scanning delivery mode. Our hypothesis for the study was that optimization of the parameters of synchrotron operation and respiratory gating can lead to greater efficiency and accuracy of respiratory gating for all modes of synchrotron-based proton treatment delivery. The hypothesis is tested in two specific aims. The specific aim #1 is to assess the efficiency of respiratory-gated proton beam delivery and optimize the synchrotron operations for the gated proton therapy. A simulation study was performed and introduced an efficient synchrotron operation pattern, called variable Tcyc. In addition, the simulation study estimated the efficiency in the respiratory gated scanning beam delivery mode as well. The specific aim #2 is to assess the accuracy of beam delivery in respiratory-gated proton therapy. The simulation study was extended to the passive scattering mode to estimate the quality of pulsed beam delivery to the residual motion for several synchrotron operation patterns with the gating technique. The results showed that variable Tcyc operation can offer good reproducible beam delivery to the residual motion at a certain phase of the motion. For respiratory gated scanning beam delivery, the impact of motion on the dose distributions by scanned beams was investigated by measurement. The results showed the threshold for motion for a variety of scan patterns and the proper number of paintings for normal and respiratory gated beam deliveries. The results of specific aims 1 and 2 provided supporting data for implementation of the respiratory gating beam delivery technique into both passive and scanning modes and the validation of the hypothesis.