George J. Takacs

Bra-breast forces generated in women with large breasts while standing and during treadmill running: implications for sports bra design

This study aimed to determine the bra-breast forces generated in women with large breasts while these women wore different levels of breast support during both upright standing and treadmill running. The mean bilateral vertical component of the bra-breast force in standing was 11.7 ± 4.6 N, whereas during treadmill running the mean unilateral bra-breast force was 8.7 ± 6.4 N and 14.7 ± 10.3 N in the high and low support conditions, respectively. Furthermore, breast mass was significantly correlated with vertical breast displacement (R(2) = 0.62) in the high support condition. The wide range of breast masses of women with large breasts is an important consideration for designers of sports bras to ensure these bras can reduce force generation and breast discomfort by providing a high level of breast support while these women participate in physical activity.

Microbeam radiation therapy: a Monte Carlo study of the influence of the source, multislit collimator, and beam divergence on microbeams.

Microbeam radiation therapy (MRT) is a new oncology method currently under development for the treatment of inoperable pediatric brain tumors. Monte Carlo simulation, or the computational study of radiation transport in matter, is often used in radiotherapy to theoretically estimate the dose required for treatment. However, its potential use in MRT dose planning systems is currently hindered by the significant discrepancies that have been observed between measured and theoretical dose and the PVDR (peak to valley dose ratio). The need to resolve these discrepancies is driven by the desirability of making MRT available to humans in the next few years. This article aims to resolve some of the discrepancies by examining the simplifications adopted in previous MRT Monte Carlo studies, such as the common practice of commencing microbeam transport on the surface of the target which neglects the influence of the distributed synchrotron source, multislit collimator, and the beam divergence between them. This article uses PENELOPE Monte Carlo simulation to investigate the influence of these beamline components upstream of the target on the lateral dose profiles and PVDRs of an array of 25 microbeams. It also compares the dose profiles and PVDRs of a microbeam array produced from a single simulation (full array) to those produced from the superposition of a single microbeam profile (sup array). The effect of modeling the distributed source and the beam divergence was an increase in the absorbed dose in the penumbral and valley regions of the microbeam profiles. Inclusion of the multislit collimator resulted in differences of up to 5 microm in the FWHM of microbeam profiles across the array, which led to minor variations in the corresponding PVDR yields.

Edge-on face-to-face MOSFET for synchrotron microbeam dosimetry: MC modeling

The dosimetry of X-ray microbeams using MOSFETs results in an asymmetrical beam profile due to a lack of lateral charged particle equilibrium. Monte Carlo simulations were carried out using PENELOPE and GEANT4 codes to study this effect and a MOSFET on a micropositioner was scanned in the microbeam. Based on the simulations a new method of microbeam dosimetry is proposed. The proposed edge-on face-to-face (EOFF) MOSFET detector, a die arrangement proposed here for the first time, should alleviate the asymmetry. Further improvement is possible by thinning the silicon body of the MOSFET.

Design and simulation of continuous scintillator with pixellated photodetector

Presents results of simulations performed as part of the development of a gamma-ray detector module comprising a nonpixellated scintillator and pixellated photodiode detector. The simulations have been carried out to determine the effect of surface treatment and dimensions of the scintillator on the ability to determine the two-dimensional position of interaction. A set of 32 different combinations of surface treatments have been considered for each crystal size. Scintillator dimensions considered have been 25/spl times/25/spl times/(3-6 mm/sup 3/). For scintillator thicknesses at the low end of this range, an average accuracy of 0.5-0.6 mm is achievable for many different surface treatments. At the higher end of the thickness range, 6 mm, the average accuracy reduces to around 0.7 mm and is more dependent on the surface treatment.

In vivo dosimetry and seed localization in prostate brachytherapy with permanent implants

This paper reports on the development of an interactive, intraoperative dose planning system for seed implant brachytherapy in cancer treatment. This system involves in-vivo dosimetry and the ability to determine implanted seed positions. The first stage of this project is the development of a urethral alarm probe to measure the dose along the urethra during a prostate brachytherapy treatment procedure. Ultimately the system will be used to advise the physicians upon reaching a preset dose rate or dose after total seed decay in urethra during the seed placement. The second stage is the development of a method and instrumentation for in-vivo measurements of the location of implanted seeds in the same frame as for dose planning, and using these in intraoperative treatment planning. We have developed a silicon mini-detector and preamplifier/amplifier system to satisfy the spectroscopic requirements of the urethral probe. This technique will avoid complications related to overdosing the urethra and the rectum.

Intraoperative solid-state based urethral dosimetry in low dose rate prostate brachytherapy

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.

Urethral alarm probe for permanent prostate implants

We have developed a urethral dosimetry system for real time dose verification along the urethra during permanent implant prostate brachytherapy. The urethral alarm probe uses “spectroscopic dosimetry” to calculate the dose rate along the urethra in real time. The application of spectroscopic dosimetry for the urethral alarm probe was verified using Monte Carlo calculations. In phantom depth dose measurements as well as isotropy measurements were performed to verify the usefulness of the urethra alarm probe as an in vivo real time dosimeter.

A dual scintillator - dual silicon photodiode detector module for intraoperative gamma\beta probe and portable anti-compton spectrometer

A new approach has been investigated for the miniaturization and simplification of intraoperative gamma and beta probes that have recently found application in radioguided surgery and sentinel lymph node biopsy. The probe design that is based on dual annular scintillators coupled to specially designed silicon concentric dual photodiode (CDPD). This approach allows us to avoid fiber optics coupling and PMTs. Two channels readout front-end electronics including shaper amplifier attached directly to the back of the detector module has been proposed. Two geometries of Si dual photodiodes coupled to CsI(Tl) annular scintillators with light masking between them were fabricated and investigated. CDPDs have size 10 and 6 mm as well as 6 and 3 mm outer and inner diameters respectively. The spectroscopy properties of CDPD separately and coupled to CsI(Tl) dual scintillator were investigated on I-125, Co-57 and Na-22 photon sources. Both detectors have demonstrated acceptable energy resolution (10% for 511-keV) for the proposed application with FDG isotopes. In the smaller detector the amplitude of the 511 keV photopeak from outer detector was less than in inner and is related to the light collection in the current geometry. When used in coincidence mode operation we observe a significant reduction in the measured Compton continuum level relative to the photopeak which is not significantly attenuated. The spatial resolution of detector module measured in the horizontal plane was 2-mm FWHM using a 0.5-mm collimated Tc-99m source.