Biomedical subjects

N Suchowerska

Publications and source records attributed to N Suchowerska.

10 recordsLinked to original sources

PubMed2006

Optical fiber design and the trapping of Cerenkov radiation.

Cerenkov radiation is generated in optical fibers immersed in radiation fields and can interfere with signal transmission. We develop a theory for predicting the intensity of Cerenkov radiation generated within the core of a multimode optical fiber by using a ray optic approach and use it to make predictions of the intensity of radiation transmitted down the fiber in propagating modes. The intensity transmitted down the fiber is found to be dominated by bound rays with a contribution from tunneling rays. It is confirmed that for relativistic particles the intensity of the radiation that is transmitted along the fiber is a function of the angle between the particle beam and the fiber axis. The angle of peak intensity is found to be a function of the fiber refractive index difference as well as the core refractive index, with larger refractive index differences shifting the peak significantly toward lower angles. The angular range of the distribution is also significantly increased in both directions by increasing the fiber refractive index difference. The intensity of the radiation is found to be proportional to the cube of the fiber core radius in addition to its dependence on refractive index difference. As the particle energy is reduced into the nonrelativistic range the entire distribution is shifted toward lower angles. Recommendations on minimizing the quantity of Cerenkov light transmitted in the fiber optic system in a radiation field are given.

Journal Article↗

PubMed2006

A plastic scintillation dosimeter for high dose rate brachytherapy.

In vivo dose verification in brachytherapy requires a small insertable dosimeter with a real-time readout capability. Fibre optic scintillation dosimeters, consisting of a plastic scintillator coupled to an optical fibre, are one of the most promising dosimeters for this application. We have developed two sizes of the BrachyFOD scintillation dosimeter which have external diameters of 2.2 mm and 1 mm and have determined their important dosimetric characteristics (depth dose relation, angular dependence, temperature dependence, energy dependence). We have shown that the background signal created by Cerenkov and fibre fluorescence does not significantly affect the performance in most clinical geometries using an (192)Ir source from an HDR brachytherapy unit. The dosimeter design enables readout at less than 0.5 s intervals. The BrachyFOD satisfies the need for a real-time in vivo brachytherapy dosimeter.

Brachytherapy↗

PubMed2005

Clinical application of the OneDose Patient Dosimetry System for total body irradiation.

The OneDose Patient Dosimetry System (Sicel Technologies) is a new dosimeter based on metal oxide semiconductor field-effect transistor technology and designed for the in vivo measurement of patient dose during radiotherapy. In vivo dosimetry for total body irradiation (TBI) is challenging due to the extended treatment distance, low dose rates and beam spoilers. Phantom results confirm the suitability of the dosimeter for TBI in terms of inherent build-up, post-irradiation fading, accuracy, reproducibility, linearity and temperature dependence. Directional dependence is significant and should be taken into account. The OneDose dosimeters were also trialed in vivo for two TBI patients and the dose measured compared to conventional dosimeter measurements using an ionization chamber and thermoluminescent dosimeters (TLD), with agreement to within 2.2% and 3.9%, respectively. Phantom and patient results confirm that the OneDose patient dosimetry system is a practical and convenient alternative to TLDs for TBI in vivo dosimetry. For increased confidence in results with this dosimeter, we recommend that two dosimeters be used for each site of interest.

Humans↗

PubMed2005

Intrafractional motion during proton beam scanning.

Patient and internal organ motion during treatment with a scanned proton beam can introduce unplanned heterogeneities in the dose distribution throughout the irradiated volume. With static beam techniques, a margin around the target volume is added to compensate for patient and organ motion. This margin may not provide the solution with dynamic beam scanning. Intrafractional motion parallel and perpendicular to the beam axis is studied using two different scanning methods on a cubic water phantom. The direction of motion relative to the beam scanning direction as well as the method of scanning the proton beam across the target has a significant effect on the resulting dose distribution within the target volume. In the extreme cases studied here up to 100% of the target receives a dose outside the recommended limits, with a minimum dose as low as 34% of the prescribed dose.

Algorithms↗

PubMed2005

In vitro response of tumour cells to non-uniform irradiation.

This study examines differences in tumour cellular response using clonogenic cell survival between uniform and non-uniform irradiation. Cells were irradiated with a 6 MV x-ray intensity-modulated beam, in a single large flask (i.e. intercellular communication is possible) or in three small flasks (i.e. intercellular communication is inhibited across the dose gradient). For non-small-cell lung cancer and melanoma cell lines, the dose response over the entire cell culture was significantly different between freely communicating cell cultures and those with inhibited communication across the dose non-uniformity. Communicating cells exhibited poorer survival in the low dose region of the field but improved survival in the high dose region. In general, the response to non-uniform irradiation appeared to 'average out' over the entire cell culture. This was not seen when intercellular communication was inhibited. The results add strength to the body of evidence regarding bystander effects and the inter-dependence of cellular response.

Carcinoma, Large Cell↗

PubMed2005

Real-time verification of HDR brachytherapy source location: implementation of detector redundancy.

Independent treatment verification for high dose rate (HDR) brachytherapy is needed to ensure that the treatment proceeds as prescribed. In this paper, we investigate the feasibility of a proposed real-time source position verification process. This process provides immediate confirmation of the source position during the treatment, so that the treatment can be aborted and modified if necessary. We show that an array of dosimeters placed on the patient's skin can independently verify the position in three dimensions. This verification was demonstrated by using a diamond detector placed in several locations on the surface of an anthropomorphic phantom. A mathematical algorithm was constructed to estimate the location of the source given a measured data set in the presence of tissue heterogeneity. The accuracy of the source localization was found to increase with the number of detectors used to compute the estimation of the source position. The resolution to which the 12 detectors can identify the location of the source was within 3 mm.

Algorithms↗

PubMed2003

High dose-rate brachytherapy source localization: positional resolution using a diamond detector.

A potential real-time source position verification process for high dose-rate (HDR) brachytherapy treatment is described. This process is intended to provide immediate confirmation that a treatment is proceeding according to plan, so that corrective action can be taken if necessary. We show that three dosimeters are in principle sufficient and demonstrate the feasibility of the process using a diamond detector and an Ir-192 source. An error analysis including all identified sources of error shows that this detector is capable of locating the distance to the source to within 2 mm for distances up to 12 cm. This positional accuracy is less than the diameter of typical HDR catheters indicating that a diamond detector can be used to accurately determine the distance to the source. The uncertainty in the distance is found to increase with distance.

Algorithms↗

PubMed2001

Directional dependence in film dosimetry: radiographic and radiochromic film.

The trend towards conformal, intensity modulated radiotherapy treatments has established the need for a true integrating dosimeter. In traditional radiotherapy, radiographic film dosimetry is commonly used. The accuracy and reproducibility of film optical density as an indicator of dose is influenced by several variables, including the chemical processing conditions. As a result radiochromic film, with all the advantages of radiographic film but without the need for chemical processing, has increased in popularity, although the low-dose sensitivity of radiochromic film does remain a disadvantage for some experiments. Several studies have investigated the reproducibility of radiochromic film results, but none have specifically addressed the well-known directional dependence seen with traditional radiographic film. In this study, the directional dependence of radiographic (Kodak X-omat V) and radiochromic (Gafchromic) films were measured. It was found that both films over responded when exposed parallel to the central axis of the beam as opposed to perpendicular exposure. An attempt is made to explain the reason for the responses of both films in terms of spectral effects and the air gap between the phantom segments. Although radiographic film exposed parallel rather than perpendicular to the central axis of the beam exhibits a measured difference in film response at depth, this over response does not occur when the extent of the film is restricted to a small region at the centre of the phantom (in this case an air gap is not introduced across the phantom). This suggests that it is the air gap rather than the orientation of the film that is the cause of the over response. Furthermore, when film occupies a slice through the entire phantom an over response occurs for both radiographic and radiochromic film, indicating that spectral effects are not the cause.

Film Dosimetry↗

PubMed1999

Perturbation of radiotherapy beams by radiographic film: measurements and Monte Carlo simulations.

Radiographic film is an established practical tool used in the measurement of the dose distribution for radiotherapy purposes. The accuracy and reproducibility of film optical density as an indicator of dose has been associated with several factors including photon energy, processing conditions and film plane orientation. Few studies have investigated the factors causing variability in film dosimetry, due to the difficulty of separating the individual contributions. The effect that a sheet of radiographic film in a water phantom has on its response to a 6 MV photon and a cobalt-60 teletherapy beam, when orientated perpendicular and parallel to the beam central axis, is reported. Monte Carlo generated spectra were used to calculate collision kerma (Kcoll) for water and film elements. Measured and calculated results indicate a potential over-response at 25 cm depth of the order of 14 +/- 2.4% and 18 +/- 6.0% respectively for 6 MV photons and 15 +/- 3.4% and 32 +/- 4.5% respectively for a cobalt beam. For film exposed parallel as compared to perpendicular to the central axis of the beam, the calculated results suggest an explanation in terms of the predominantly forward directed secondary electrons for the measured difference in film response at depth. It is proposed that the difference in response of the parallel as compared to perpendicular exposed film be due to the predominantly 'upstream' photon interactions giving rise to energy deposition in film. The simulations indicate that the variation with depth of relative energy imparted in film and water elements correlates with the observed variation in film response with depth.

Energy Transfer↗

PubMed1997

The validity of using radiographic film for radiotherapy dosimetry.

Radiographic film is routinely used to obtain dosimetric information about therapy treatment beams. One source of inaccuracy is the variability of the chemical processing of the radiographic film. Several processors, film types and two sources (light and x-rays) were used to investigate the reproducibility of film processing for valid film dosimetry. Particular attention is paid to films commonly used in radiation therapy. The results suggest that for this series of film, given the same exposure, the variability in processing may result in an error of +/- 3.3% in optical density, which would lead to an error of +/- 4.4% in indicated dose. This level of inaccuracy is typical for both point and relative dose estimates. These results indicate that film should not be used as a point or relative dosimeter, unless the combination of film type, exposure, processing and reading have been specifically validated.

Equipment Design↗