We evaluated the OCTOPUS-ONE research laser CT scanner developed and manufactured by MGS Research, Inc. (Madison, CT). The scanner is designed for imaging 3D optical density distributions in BANG gels. The scanner operates in a translate-rotate configuration with a single scanning laser beam. The rotating cylindrical gel phantom is immersed in a refractive index matching solution and positioned at the center of a square tank made of plastic and glass. A stationary polarized He-Ne laser beam (633 nm) is reflected from a mirror moving parallel to the tank wall and scans the gel. Another mirror moves synchronously along the opposite side of the tank and collects the transmitted light and sends it to a single stationary silicon photodetector. A filtered backprojection algorithm is used to reconstruct projection data in a plane. The laser-mirrors-detector assembly is mounted on a horizontal platform that moves vertically for slice selection. We have tested the mechanical and optical setup, projection centering on the axis of rotation, linearity, and spatial resolution. We found the optical detector to respond linearly to transmitted light from control samples. The spatial resolution of the scanner was determined by employing a split field resolution technique. We obtained the horizontal and vertical full widths at half maxima of the laser beam intensity profiles as 0.6 and 0.8 mm, respectively. Dose calibration tests of the gel were performed using a nine-field (2 x 2 cm2 each) dose pattern irradiated at different dose levels. Finally, we compared gel-derived 2D planar dose distribution against radiochromic film measured dose distribution for both the nine-field and a uniform 5 x 5 cm2 field of 6 MV x rays. Very similar dose distributions were observed in gel and radiochromic film except in regions of steep dose gradient and highest dose. A dose normalization of 15.6% was required between the two dosimeters due to differences in overall radiation response. After normalization, analysis using the gamma evaluation showed that the radiochromic film and gel-measured dose distributions differed by a maximum gamma of 1.3 using 5% and 1.5 mm dose difference and distance-to-agreement criteria. The optical CT scanner has great potential as a 3D dosimeter, but a few refinements and further testing are necessary before its routine clinical use.

Background and purpose: The objective was to determine diode characteristics before actual dose verification on human phantom and patients. Materials and methods:The reliability and stability of equipment, signal stability, precision, dose response linearity, field flatness, perturbation of radiation dose, plastic to water conversion factor (K pl ), ionisation chambers (ICs) and diode calibration were determined. Correction factors for tray (CF tray ), wedge (CF wedge ), field size (CF FS ), SSD (CF SSD ), angle (CF angle ) and block (CF block ) were found. Patient dose monitor, Isorad diode (n-type) and IC (PTW Frieburg), Co-60 unit (Theratron), ATOM Adult male human phantom (Model 701-D, CIRS) were used.Results and conclusion: Good signal stability, precise data, and linear dose response, variation of 0?500% and 5?000% in field flatness and perturbation tests, respectively, were noted. K pl was 1?006 for IC PTW Frieburg TW30013, 0114. The diode calibration factor was 0?989. CF tray , CF FS , CF SSD , CF angle , CF block were 1?001, 1?001, 0?997, 1?006 and 0?990, respectively. CF wedge were 1?024, 1?030 and 1?038 for 308, 458 and 608 wedges, respectively. The verification of above correction factors (CFs) on Nasopharynx and lung of human phantom was also done.

Sulfur isotopes in SF6 molecules have been enriched, in a laboratory experiment, using tuned laser radiation to excite a particular sulfur isotopic molecule and inhibit its condensation on the cooled annulus inside of the chamber. The evidence of enrichment was determined by examining the residual gas with a Fourier Transform lnfra Red Spectrometer. The enrichment was observed during a transient experiment in which the temperature of the condensing surface was gradually decreased, and gas pressure of the SF6 molecules was in the range of 8 Torr (0.01 atmospheres). These results show that excitation to a single excited level can create differential rates of condensation so as to achieve an enrichment factor of approximately 2.0 in a single stage.

PurposeThe main aim was to use pre-calculated correction factors and calibration factors for measurement of accuracy of dose delivery before implementation of such in vivo dosimetry on real patients visiting for first radiation treatment. These factors were verified by generating the most common treatment plans on human phantom except for breast and colon using cobalt-60 unit.Materials and methodsSix treatment plans were generated, i.e. nasopharynx, bladder, prostate, brain, larynx and lung of human phantom, total 18 fields were planned keeping in view the correction factors which are to be verified. MULTIDATA Decision Support System 2.5, Shimadzu simulator, Isorad diode-n type, electrometer patient dose monitor and ATOM Adult male human phantom were used.Results and conclusionFor 18 fields, the dose delivery was accurate in the range 0·29–6·74%. The deviation between measured and expected doses to nasopharynx, lung, bladder, prostate, brain and larynx cases of human phantom ranged from 1·44–3·89%, 0·29–0·54%, 0·44–6·18%, 0·54–5·16%, 0·33–4·90%, 5·58–6·74%, respectively. In 30 palliative patient cases, the first radiation treatment was also monitored. The accuracy of dosimety ranged from 1·05% to 5·35%. This study is helpful to identify areas of improvement in treatment of patients like quality control/quality assurance (QA) of treatment planning system, beam data modifications, machine repair maintenance, QA audit in radiotherapy.

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