Copyright (c) 2009 All rights reserved. http://works.bepress.com/arozenfeld Recent documents in Professor A. Rozenfeld en-us Sun, 31 May 2009 03:36:31 PDT 3600 http://works.bepress.com/arozenfeld/33 http://works.bepress.com/arozenfeld/33 Mon, 02 Feb 2009 14:22:34 PST Measurements were performed to assess the dose equivalent outside a primary proton treatment field, using a silicon-on-insulator (SOI) microdosimeter. The SOI microdosimeter was placed on the surface of an anthropomorphic phantom and dose equivalents were determined as a function of lateral distance from a typical passively scattered and modulated prostate treatment field. Measurements were also completed within a polystyrene plate phantom as a function of depth for a distance of 5 cm from the field edge, as function of lateral distance from field edge at two different depths, and as a function of distance from the distal edge on the central beam axis. The dose equivalent at the surface of the anthropomorphic phantom decreases from 3.9 to 0.18 mSv/Gy when the lateral distance from the proton field edge increases from 2.5 to 60 cm. Measurements along the proton depth dose distribution at a constant distance of 5 cm from the primary field edge indicate a decrease in dose equivalent as a function of depth, with a 38% decrease relative to the surface dose at a depth of 5 cm in polystyrene. Measurements completed as a function of lateral distance from the primary field at two separate depths within polystyrene illustrate a convergence of the dose equivalent at approximately 20 cm from the primary field edge. Past the distal edge of the spreadout Bragg peak dose equivalents decrease exponentially for increasing distance, with an initial value of 1.6 mSv/Gy at 0.6 cm from the distal edge. Silicon microdosimetry measurements were also compared with published results obtained utilizing different measurement techniques. This study demonstrates the applicability of SOI microdosimetry in determining the dose equivalent outside proton treatment fields, and provides valuable information on the dose equivalent both at the surface and at depth experienced by prostate cancer patients treated with protons. A. Wroe http://works.bepress.com/arozenfeld/32 http://works.bepress.com/arozenfeld/32 Tue, 03 Jun 2008 15:38:11 PDT Present Positron Emission Tomography (PET) detectors suffer from degradation of the spatial resolution due to the lack of depth-of-interaction (DOI) information leading to uncertainty in deducing the Lines of Response (LOR) between coincident events. The Centre for Medical Radiation Physics at the University of Wollongong has developed a novel detector module which will provide depth of interaction information while retaining the sensitivity of current scanners. This will result in superior imaging together with the ability to locate smaller lesions. This work focuses on preliminary investigations of the suitability of replacing the bulky scintillator crystals and photomultiplier tubes of traditional PET detector modules with compact 3 × 3 × 3 mm3 LYSO scintillator crystals individually coupled to Si photdetectors. The simulations were undertaken using GATE, a high level front end for GEANT4, specifically designed for use in the simulation of PET and SPECT. The simulation results quantify the level of improvement that can be potentially gained using a new detector module capable of providing a uniform spatial resolution across the entire field of view (FOV). Data is analysed using a newly developed sinogram binning technique. Simulation results show a resolution of 1.6 mm FWHM can be obtained for the entire FOV of this scanner (approximately 230 mm). This represents an improvement of approximately 75% in the resolution at the edges of field of view compared to traditional detector module design. Comparison of spatial resolution data for the novel detector module and phoswich detectors is also presented. L. Perera http://works.bepress.com/arozenfeld/31 http://works.bepress.com/arozenfeld/31 Wed, 28 May 2008 11:37:06 PDT This paper presents in phantom testing of a recently developed intraoperative minidosimetry system, designed to measure the dose along the urethra during low dose rate prostate brachytherapy. This system is based on a silicon minidetector and uses spectroscopy to calculate the localized dose from the treatment radiation. The minidosimetry system was demonstrated to be operational at body temperature, with a near isotropic response to radiation at all angles. Phantom measurements have shown the minidosimetry system to measure the dose from multiple seeds to within 5% of planning system calculated doses. This system is an ideal complement to ultrasound guided seed placement in providing online direct dosimetry during seed implantation, as well as providing dose planning system verification through post implant dosimetry. D. L. Cutajar http://works.bepress.com/arozenfeld/30 http://works.bepress.com/arozenfeld/30 Wed, 28 May 2008 11:37:03 PDT We have previously demonstrated the potential of multi-pinhole coded apertures when used in conjunction with compact pixelated detectors for high resolution, high sensitivity small animal SPECT. We are now constructing a prototype SPECT system with three such detectors mounted on a rotating gantry. Each detector comprises a 12 cm diameter circular array of NaI(Tl) crystals, each 1/spl times/1/spl times/5 mm/sup 3/ on a 1.25 mm pitch. Each crystal array is coupled to a Hamamatsu R3292 12.7 cm diameter PS-PMT. Signals from the three detectors are read out by a custom subtractive resistive circuit and multiplexed. Data are acquired by a National Instruments PCI-6110E board running on a Macintosh dual processor G4 computer under Kmax software control. Images are reconstructed using a 3D iterative MAP-EM algorithm based on a multi-pinhole forward and back projector. The trade-off between contrast and variance was studied by simulation for a number of multi-pinhole configurations. We also performed initial planar imaging studies on one of the detectors. Our results indicate that spatial resolution approaching 1 mm full width at half maximum (FWHM) can be achieved with a single pinhole aperture, while improved contrast and variance may result from using optimized multi-pinhole apertures. S. R. Meikle http://works.bepress.com/arozenfeld/29 http://works.bepress.com/arozenfeld/29 Wed, 28 May 2008 11:37:00 PDT The timing properties of a silicon-on-insulator microdosimeter for medical and space applications have been studied using an ion microprobe. These measurements were used with a pulse-shape discrimination technique to render the microdosimeter insensitive to ion strikes outside the ideal sensitive volume. These improvements have resulted in a microdosimeter with a cubic sensitive volume with dimensions 10/spl times/10/spl times/10 /spl mu/m/sup 3/, a charge collection spectrum close to Gaussian for a monoenergetic source, and a decreased sensitivity to radiation damage. I. Cornelius http://works.bepress.com/arozenfeld/28 http://works.bepress.com/arozenfeld/28 Wed, 28 May 2008 11:36:55 PDT Sufficient skin dose needs to be delivered by a radiotherapy chest wall treatment regimen to ensure the probability of a near surface tumor recurrence is minimized. To simulate a chest wall treatment a hemicylindrical solid water phantom of 7.5 cm radius was irradiated with 6 MV x-rays using 20320 cm2 and 10320 cm2 fields at 100 cm source surface distance ~SSD! to the base of the phantom. A surface dose profile was obtained from 0 to 180°, in 10° increments around the circumference of the phantom. Dosimetry results obtained from radiochromic film ~effective depth of 0.17 mm! were used in the investigation, the superficial doses were found to be 28% ~of Dmax) at the 0° beam entry position and 58% at the 90° oblique beam position. Superficial dose results were also obtained using extra thin thermoluminescent dosimeters ~TLD! ~effective depth 0.14 mm! of 30% at 0°, 57% at 90°, and a metal oxide semiconductor field effect transistor ~MOSFET! detector ~effective depth 0.5 mm! of 43% at 0°, 62% at 90°. Because the differences in measured superficial doses were significant and beyond those related to experimental error, these differences are assumed to be mostly attributable to the effective depth of measurement of each detector. We numerically simulated a bolus on/bolus off technique and found we could increase the coverage to the skin. Using an alternate ''bolus on,'' ''bolus off'' regimen, the skin would receive 36.8 Gy at 0° incidence and 46.4 Gy at 90° incidence for a prescribed midpoint dose of 50 Gy. From this work it is evident that, as the circumference of the phantom is traversed the SSD increases and hence there is an inverse square fluence fall-off, this is more than offset by the increase in skin dose due to surface curvature to a plateau at about 90°. Beyond this angle it is assumed that beam attenuation through the phantom and inverse square fall-off is causing the surface dose to reduce. K. Y. Quach http://works.bepress.com/arozenfeld/27 http://works.bepress.com/arozenfeld/27 Wed, 28 May 2008 11:36:53 PDT An ion transport code was developed for simulating ionization energy deposition by energetic ions in sensitive volumes of complex structures. The code was used to simulate recent microdosimetry measurements performed with silicon-on-insulator (SOI) microdosimeters in Fast Neutron Therapy (FNT). I. Cornelius http://works.bepress.com/arozenfeld/26 http://works.bepress.com/arozenfeld/26 Wed, 28 May 2008 11:36:49 PDT New nonionizing energy losses (NIEL) sensors based on silicon planar p-i-n diodes of different geometry have been investigated and their response to fast neutron field compared with bulk diodes. The possibility of obtaining a wide range of sensitivities in these NIEL sensors simultaneously with measurements of IEL has been demonstrated. A. Rosenfeld http://works.bepress.com/arozenfeld/25 http://works.bepress.com/arozenfeld/25 Wed, 28 May 2008 11:36:46 PDT Reported MOSFET measurements concern mostly external radiotherapy and in vivo dosimetry. In this paper, we apply the technique for absolute dosimetry in the context of HDR brachytherapy using an 192Ir source. Measured radial dose rate distributions in water for different planes perpendicular to the source axis are presented and special attention is paid to the calibration of the R and K type detectors, and to the determination of appropriate correction factors for the sensitivity variation with the increase of the threshold voltage and the energy dependence. The experimental results are compared with Monte Carlo simulated dose rate distributions. The experimental results show a good agreement with the Monte Carlo simulations: the discrepancy between experimental and Monte Carlo results being within 5% for 82% of the points and within 10% for 95% of the points. Moreover, all points except two are found to lie within the experimental uncertainties, confirming thereby the quality of the results obtained. V. O. Zilio http://works.bepress.com/arozenfeld/24 http://works.bepress.com/arozenfeld/24 Wed, 28 May 2008 11:36:43 PDT The response of a solid state microdosimeter based on semiconductor on insulator (SOI) technology to a 238PuBe neutron source was investigated. Simulations of the device response using the GEANT4 Monte Carlo Toolkit are also presented. The microdosimetric spectra was measured for lineal energies above 1 keV/􀁐m. The possible application of the SOI microdosimeter for radiation protection applications in the form of a personnel microdosimeter is suggested. M. I. Reinhard