Using NMR spectroscopy to investigate the role played by copper in prion diseases.

Prion diseases are a group of rare neurodegenerative disorders that develop as a result of the conformational conversion of normal prion protein (PrPC) to the disease-associated isoform (PrPSc). The mechanism that actually causes disease remains unclear. However, the mechanism underlying the conformational transformation of prion protein is partially understood-in particular, there is strong evidence that copper ions play a significant functional role in prion proteins and in their conformational conversion. Various models of the interaction of copper ions with prion proteins have been proposed for the Cu (II)-binding, cell-surface glycoprotein known as prion protein (PrP). Changes in the concentration of copper ions in the brain have been associated with prion diseases and there is strong evidence that copper plays a significant functional role in the conformational conversion of PrP. Nevertheless, because copper ions have been shown to have both a positive and negative effect on prion disease onset, the role played by Cu (II) ions in these diseases remains a topic of debate. Because of the unique properties of paramagnetic Cu (II) ions in the magnetic field, their interactions with PrP can be tracked even at single atom resolution using nuclear magnetic resonance (NMR) spectroscopy. Various NMR approaches have been utilized to study the kinetic, thermodynamic, and structural properties of Cu (II)-PrP interactions. Here, we highlight the different models of copper interactions with PrP with particular focus on studies that use NMR spectroscopy to investigate the role played by copper ions in prion diseases.

Customized double-shell immobilization device combined with VMAT radiation treatment of basosquamous cell carcinoma of the scalp.

Malignancies with a superficial involvement of the scalp/skull present technical challenges for radiation-treatment-planning, such as achieving skin coverage with the prescribed dose and with the desirable conformity, homogeneity, and lower brain dose. We report a radiotherapy treatment technique for a patient diagnosed with diffuse basosquamous cell carcinoma of the scalp and adjacent skull-bone. This study presents the plan's quality parameters, patient's dosimetry, and patient's outcome. The patient was treated using volume-modulated-arc therapy (VMAT) and a double-shell-bolus full-head device (DSBFD) designed for patient immobilization and better skin coverage. A VMAT plan was generated using an Eclipse treatment-planning system for a prescribed dose of 60 Gy in 30 fractions. The treatment plan was analyzed to determine the conformity index (CI), the homogeneity index (HI), the target-coverage, and the dose to the organs-at-risk (OARs). Skin-doses were measured using optically stimulated luminescence (OSL) dosimeters. Clinical follow-up was performed by the radiation oncologist during and after the course of radiotherapy. With regard to planning target volume (PTV) coverage, the V95 was 99%. The measured and calculated dose to the skin was in the range 100-108% of the prescribed dose. The mean brain-PTV dose was 711 cGy. The CI and HI were 1.09 and 1.08, respectively. The mean positioning accuracy for the patient over the course of treatment was within 2 mm. The measured accumulated skin dose and planning dose was agreed within 2%. Clinical examination of the patient 6 months after radiotherapy showed good response to the treatment and a 90% reduction in scarring. The DSBFD technique combined with RapidArc treatment was useful in terms of the target dose distribution and coverage. Daily patient alignment was found very precise, reproducible and less time-consuming.

A methodology for on-board CBCT imaging dose using optically stimulated luminescence detectors.

Cone-beam computed tomography CBCT systems are used in radiation therapy for patient alignment and positioning. The CBCT imaging procedure for patient setup adds substantial radiation dose to patient's normal tissue. This study pre-sents a complete procedure for the CBCT dosimetry using the InLight optically-stimulated-luminescence (OSL) nanoDots. We report five dose parameters: the mean slice dose (DMSD); the cone beam dose index (CBDIW); the mean volume dose (DMVD); point-dose profile, D(FOV); and the off-field Dose. In addition, CBCT skin doses for seven pelvic tumor patients are reported. CBCT-dose mea-surement was performed on a custom-made cylindrical acrylic body phantom (50cm length, 32cm diameter). We machined 25 circular disks (2 cm thick) with grooves and holes to hold OSL-nanoDots. OSLs that showed similar sensitivities were selected and calibrated against a Farmer-type ionization-chamber (0.6 CT) before being inserted into the grooves and holes. For the phantom scan, a standard CBCT-imaging protocol (pelvic sites: 125 kVp, 80 mA and 25 ms) was used. Five dose parameters were quantified: DMSD, CBDIW, DMVD, D(FOV), and the off-field dose. The DMSD for the central slice was 31.1 ± 0.85 mGy, and CBDIW was 34.5± 0.6 mGy at 16cm FOV. The DMVD was 25.6 ± 1.1 mGy. The off-field dose was 10.5 mGy. For patients, the anterior and lateral skin doses attributable to CBCT imaging were 39.04 ± 4.4 and 27.1 ± 1.3 mGy, respectively.OSL nanoDots were convenient to use in measuring CBCT dose. The method of selecting the nanoDots greatly reduced uncertainty in the OSL measurements. Our detailed calibration procedure and CBCT dose measurements and calculations could prove useful in developing OSL routines for CBCT quality assessment, which in turn gives them the property of high spatial resolution, meaning that they have the potential for measurement of dose in regions of severe dose-gradients.

A qualitative and quantitative analysis of radiation dose and image quality of computed tomography images using adaptive statistical iterative reconstruction.

Image quality is a key issue in radiology, particularly in a clinical setting where it is important to achieve accurate diagnoses while minimizing radiation dose. Some computed tomography (CT) manufacturers have introduced algorithms that claim significant dose reduction. In this study, we assessed CT image quality produced by two reconstruction algorithms provided with GE Healthcare's Discovery 690 Elite positron emission tomography (PET) CT scanner. Image quality was measured for images obtained at various doses with both conventional filtered back-projection (FBP) and adaptive statistical iterative reconstruction (ASIR) algorithms. A stan-dard CT dose index (CTDI) phantom and a pencil ionization chamber were used to measure the CT dose at 120 kVp and an exposure of 260 mAs. Image quality was assessed using two phantoms. CT images of both phantoms were acquired at tube voltage (kV) of 120 with exposures ranging from 25 mAs to 400 mAs. Images were reconstructed using FBP and ASIR ranging from 10% to 100%, then analyzed for noise, low-contrast detectability, contrast-to-noise ratio (CNR), and modulation transfer function (MTF). Noise was 4.6 HU in water phantom images acquired at 260 mAs/FBP 120 kV and 130 mAs/50% ASIR 120 kV. The large objects (fre-quency < 7 lp/cm) retained fairly acceptable image quality at 130 mAs/50% ASIR, compared to 260 mAs/FBP. The application of ASIR for small objects (frequency >7 lp/cm) showed poor visibility compared to FBP at 260 mAs and even worse for images acquired at less than 130 mAs. ASIR blending more than 50% at low dose tends to reduce contrast of small objects (frequency >7 lp/cm). We concluded that dose reduction and ASIR should be applied with close attention if the objects to be detected or diagnosed are small (frequency > 7 lp/cm). Further investigations are required to correlate the small objects (frequency > 7 lp/cm) to patient anatomy and clinical diagnosis.

Feasibility study of using MOSFET detectors for in vivo dosimetry during permanent low-dose-rate prostate implants.

PURPOSE: To investigate the feasibility of using new micro-MOSFET detectors for QA and in vivo dosimetry of the urethra during transperineal interstitial permanent prostate implants (TIPPB). METHODS AND MATERIALS: This study involves measurements for several patients who have undergone the implant procedure with iodine-125 seeds. A new micro-MOSFET detector is used as a tool for in vivo measurement of the initial dose rate within the urethra. MOSFETs are calibrated using a single special order calibration seed. The angular response is investigated in a 100 kVp X-ray beam. RESULTS: micro-MOSFETs are found to have a calibration factor of 0.03 cGy/mV for low energy X-rays and a high isotropic response (within 2.5%). Prostate volume and shape changes during TIPPB due to edema caused by the trauma of needle insertion, making it difficult to achieve the planned implant geometry and hence the desired dose distribution. MOSFET measurements help us to evaluate the overall quality of the implant, by analyzing the maximum dose received by urethra, the prostate base coverage, the length of the prostatic urethra that is irradiated, and the apex coverage. CONCLUSIONS: We demonstrate that ease of use, quick calibration and the instantaneous reading of accumulated dose make micro-MOSFETs feasible for in vivo dosimetry during TIPPB.