a technique for spatial resolution improvement in helium beam radiography

n/

Search for Doubly-Charged Higgs Boson Production at HERA

A search for the single production of doubly-charged Higgs bosons H^{\pm \pm} in ep collisions is presented. The signal is searched for via the Higgs decays into a high mass pair of same charge leptons, one of them being an electron. The analysis uses up to 118 pb^{-1} of ep data collected by the H1 experiment at HERA. No evidence for doubly-charged Higgs production is observed and mass dependent upper limits are derived on the Yukawa couplings h_{el} of the Higgs boson to an electron-lepton pair. Assuming that the doubly-charged Higgs only decays into an electron and a muon via a coupling of electromagnetic strength h_{e \mu} = \sqrt{4 \pi \alpha_{em}} = 0.3, a lower limit of 141 GeV on the H^{\pm\pm} mass is obtained at the 95% confidence level. For a doubly-charged Higgs decaying only into an electron and a tau and a coupling h_{e\tau} = 0.3, masses below 112 GeV are ruled out.Comment: 15 pages, 3 figures, 1 tabl

Surface dosimetry for breast radiotherapy in the presence of immobilization cast material

Curative breast radiotherapy typically leaves patients with varying degrees of cosmetic damage. One problem interfering with cosmetically acceptable breast radiotherapy is the external contour for large pendulous breasts which often results in high doses to skin folds. Thermoplastic casts are often employed to secure the breasts to maintain setup reproducibility and limit the presence of skin folds. This paper aims to determine changes in surface dose that can be attributed to the use of thermoplastic immobilization casts. Skin dose for a clinical hybrid conformal/IMRT breast plan was measured using radiochromic film and MOSFET detectors at a range ofwater equivalent depths representative of the different skin layers. The radiochromic film was used as an integrating dosimeter, while the MOSFETs were used for real-time dosimetry to isolate the contribution of skin dose from individual IMRT segments. Strips of film were placed at various locations on the breast and the MOSFETs were used to measure skin dose at 16 positions spaced along the film strips for comparison of data. The results showed an increase in skin dose in the presence of the immobilization cast of up to 45.7% and 62.3% of the skin dose without the immobilization cast present as measured with Gafchromic EBT film and MOSFETs, respectively. The increase in skin dose due to the immobilization cast varied with the angle of beam incidence and was greatest when the beam was normally incident on the phantom. The increase in surface dose with the immobilization cast was greater under entrance dose conditions compared to exit dose conditions

Local heterogeneities in early batches of EBT2 film: A suggested solution

To enhance the utility of radiochromic films for high-resolution dosimetry of small and modulated radiotherapy fields, we propose a means to negate the effects of heterogeneities in EBT2 (and other) films. The results of using our simple procedure for evaluating radiation dose in EBT2 film are compared with the results of using the manufacturer's recommended procedure as well as a procedure previously established for evaluating dose in older EBT film. It is shown that Newton's ring-like scanning artefacts can be avoided through the use of a plastic frame, to elevate the film above the scanner's surface. The effects of film heterogeneity can be minimized by evaluating net optical density, pixelwise, as the logarithm of the ratio of the red-channel pixel value in each pixel of each irradiated film to the red-channel pixel value in the same pixel in the same film prior to irradiation. The application of a blue-channel correction was found to result in increased noise. It is recommended that, when using EBT2 film for radiotherapy quality assurance, the films should be scanned before and after irradiation and analysed using the method proposed herein, without the use of the blue-channel correction, in order to produce dose images with minimal film heterogeneity effects

Dynamic range and resolving power of the Timepix detector to heavy charged particles

The spectrometric and particle tracking response of the Timepix detector for charged particle detection was examined for energetic (i.e. penetrating) heavy charged particles in a wide range of energies and directions. The aim of this studywas to examine the detector’s resolving power including particles approaching the minimum-ionizing regime, in particular energetic protons. The per-pixel energy range, of importance namely for heavy charged particles, was also investigated. This work complements and extends the ongoing task to analyze and describe the response and resolving power of the detector in a wide range of particle types, energy (energy loss) and direction. The methodology of event discrimination in terms of these degrees of freedom was expanded and refined. Resolution and event classification were based on analyses of cluster morphology parameters together with spectrometric, tracking and correlated derived quantities such as linearenergy- transfer (LET) and ratio cluster height to cluster path length

Medipix detectors in radiation therapy for advanced quality-assurance

Spectroscopy-based photon-counting detector systems, Medipix, have many applications in medicine. Medipix detectors benefit from providing energy information as well as high spatial resolution. In this article, a review of Medipix detector technology applied to medicine and imaging techniques are presented. The technology has been used to develop quality assurance (QA) measurement devices in radiation-based treatments. A gamma camera system for radiotherapy has been developed to measure dose delivered to prostate treatments in real-time. The advantage of a high-resolution detector has been utilized in proton and heavy ion therapy for dose QA, measuring the charge particle spectra, and beam geometry for mini-beams. Applications in medical imaging using helium ion beams have been investigated to replace CT for ion beam radiotherapy. This technique provides many advantages over conventional CT such as high-resolution imaging and spectroscopy-based information for planning in helium ion treatments. The Medipix technology has shown it can be broadly applied in radiation and particle therapy applications for accurate QA as well as proving high-resolution imaging in medicine