High power laser production of short-lived isotopes for positron emission tomography

Positron emission tomography (PET) is a powerful diagnostic/imaging technique requiring the production of the short-lived positron emitting isotopes C-11, N-13, O-15 and F-18 by proton irradiation of natural/enriched targets using cyclotrons. The development of PET has been hampered due to the size and shielding requirements of nuclear installations. Recent results show that when an intense laser beam interacts with solid targets, megaelectronvolt (MeV) protons capable of producing PET isotopes are generated. This report describes how to generate intense PET sources of C-11 and F-18 using a petawatt laser beam. The work describing the laser production of F-18 through a (p,n) O-18 reaction, and the subsequent synthesis of 2-[F-18] is reported for the first time. The potential for developing compact laser technology for this purpose is discussed.

Characterization of Li-7(p,n)Be-7 neutron yields from laser produced ion beams for fast neutron radiography

Investigations of Li-7(p,n)Be-7 reactions using Cu and CH primary and LiF secondary targets were performed using the VULCAN laser [C.N. Danson , J. Mod. Opt. 45, 1653 (1997)] with intensities up to 3x10(19) W cm(-2). The neutron yield was measured using CR-39 plastic track detector and the yield was up to 3x10(8) sr(-1) for CH primary targets and up to 2x10(8) sr(-1) for Cu primary targets. The angular distribution of neutrons was measured at various angles and revealed a relatively anisotropic neutron distribution over 180degrees that was greater than the error of measurement. It may be possible to exploit such reactions on high repetition, table-top lasers for neutron radiography. (C) 2004 American Institute of Physics.

Target charging effects on proton acceleration during high-intensity short-pulse laser-solid interactions

We report results from experiments performed at the Rutherford Appleton Laboratory using the VULCAN laser facility (I>5x10(19) W cm(-2)). Single wire targets were used, and on some shots additional objects were placed near the target. These were positioned so that they were not irradiated by the laser. Proton emission from single wire targets was observed as radially symmetric structures (

A nearly real-time high temperature laser-plasma diagnostic using photonuclear reactions in tantalum

A method of measuring the temperature of the fast electrons produced in ultraintense laser-plasma interactions is described by inducing photonuclear reactions, in particular (gamma,n) and (gamma,3n) reactions in tantalum. Analysis of the gamma rays emitted by the daughter nuclei of these reactions using a germanium counter enables a relatively straightforward near real-time temperature measurement to be made. This is especially important for high temperature plasmas where alternative diagnostic techniques are usually difficult and time consuming. This technique can be used while other experiments are being conducted. (C) 2002 American Institute of Physics.

Characterization of a gamma-ray source based on a laser-plasma accelerator with applications to radiography

The application of high intensity laser-produced gamma rays is discussed with regard to picosecond resolution deep-penetration radiography. The spectrum and angular distribution of these gamma rays is measured using an array of thermoluminescent detectors for both an underdense (gas) target and an overdense (solid) target. It is found that the use of an underdense target in a laser plasma accelerator configuration produces a much more intense and directional source. The peak dose is also increased significantly. Radiography is demonstrated in these experiments and the source size is also estimated. (C) 2002 American Institute of Physics.

Laser generation of proton beams for the production of short-lived positron emitting radioisotopes

Protons of energies up to 37 MeV have been generated when ultra-intense lasers (up to 10(20) W cm(-2)) interact with hydrogen containing solid targets. These protons can be used to induce nuclear reactions in secondary targets to produce P-emitting nuclei of relevance to the nuclear medicine community, namely C-11 and N-13 via (p, n) and (p, alpha) reactions. Activities of the order of 200 kBq have been measured from a single laser pulse interacting with a thin solid target. The possibility of using ultra-intense lasers to produce commercial amounts of short-lived positron emitting sources for positron emission tomography (PET) is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

Production of radioactive nuclides by energetic protons generated from intense laser-plasma interactions

Nuclear activation has been observed in materials exposed to the ablated plasma generated from high intensity laser-solid interactions (at focused intensities up to 2x10(19) W/cm(2)) and is produced by protons having energies up to 30 MeV. The energy spectrum of the protons is determined from these activation measurements and is found to be consistent with other ion diagnostics. The possible development of this technique for

Hospital antibiotic use and its relationship to age-adjusted comorbidity and alcohol-based hand rub consumption

SUMMARY The objective of this study was to evaluate the effect of age-adjusted comorbidity and alcohol-based hand rub on monthly hospital antibiotic usage, retrospectively. A multivariate autoregressive integrated moving average (ARIMA) model was built to relate the monthly use of all antibiotics grouped together with age-adjusted comorbidity and alcohol-based hand rub over a 5-year period (April 2005-March 2010). The results showed that monthly antibiotic use was positively related to the age-adjusted comorbidity index (concomitant effect, coefficient 1·103, P = 0·0002), and negatively related to the use of alcohol-based hand rub (2-month delay, coefficient -0·069, P = 0·0533). Alcohol-based hand rub is considered a modifiable factor and as such can be identified as a target for quality improvement programmes. Time-series analysis may provide a suitable methodology for identifying possible predictive variables that explain antibiotic use in healthcare settings. Future research should examine the relationship between infection control practices and antibiotic use, identify other infection control predictive factors for hospital antibiotic use, and evaluate the impact of enhancing different infection control practices on antibiotic use in a healthcare setting.

Mechanical characterization of the varian Exact-arm and R-arm support systems for eight aS500 electronic portal imaging devices

The aim of this study is to compare the positioning accuracy at different gantry angles of two electronic portal imaging devices (EPIDs) support arm systems by using EPID difference images as a measure for displacement. This work presents a comparison of the mechanical performance of eight Varian aS500 (Varian Medical Systems, Palo Alto, CA) EPIDs, mounted using either the Varian Exact-arm or R-arm.

Optimization of image quality and dose for Varian aS500 electronic portal imaging devices (EPIDs)

This study was carried out to investigate whether the electronic portal imaging (EPI) acquisition process could be optimized, and as a result tolerance and action levels be set for the PIPSPro QC-3V phantom image quality assessment. The aim of the optimization process was to reduce the dose delivered to the patient while maintaining a clinically acceptable image quality. This is of interest when images are acquired in addition to the planned patient treatment, rather than images being acquired using the treatment field during a patient's treatment. A series of phantoms were used to assess image quality for different acquisition settings relative to the baseline values obtained following acceptance testing. Eight Varian aS500 EPID systems on four matched Varian 600C/D linacs and four matched Varian 2100C/D linacs were compared for consistency of performance and images were acquired at the four main orthogonal gantry angles. Images were acquired using a 6 MV beam operating at 100 MU min(-1) and the low-dose acquisition mode. Doses used in the comparison were measured using a Farmer ionization chamber placed at d(max) in solid water. The results demonstrated that the number of reset frames did not have any influence on the image contrast, but the number of frame averages did. The expected increase in noise with corresponding decrease in contrast was also observed when reducing the number of frame averages. The optimal settings for the low-dose acquisition mode with respect to image quality and dose were found to be one reset frame and three frame averages. All patients at the Northern Ireland Cancer Centre are now imaged using one reset frame and three frame averages in the 6 MV 100 MU min(-1) low-dose acquisition mode. Routine EPID QC contrast tolerance (+/-10) and action (+/-20) levels using the PIPSPro phantom based around expected values of 190 (Varian 600C/D) and 225 (Varian 2100C/D) have been introduced. The dose at dmax from electronic portal imaging has been reduced by approximately 28%, and while the image quality has been reduced, the images produced are still clinically acceptable.

Octavius 4D characterization for flattened and flattening filter free rotational deliveries

Purpose: In this study the Octavius detector 729 ionization chamber (IC) array with the Octavius 4D phantom was characterized for flattening filter (FF) and flattening filter free (FFF) static and rotational beams. The device was assessed for verification with FF and FFF RapidArc treatment plans.

Methods: The response of the detectors to field size, dose linearity, and dose rate were assessed for 6 MV FF beams and also 6 and 10 MV FFF beams. Dosimetric and mechanical accuracy of the detector array within the Octavius 4D rotational phantom was evaluated against measurements made using semiflex and pinpoint ionization chambers, and radiochromic film. Verification FF and FFF RapidArc plans were assessed using a gamma function with 3%/3 mm tolerances and 2%/2 mm tolerances and further analysis of these plans was undertaken using film and a second detector array with higher spatial resolution.

Results: A warm-up dose of >6 Gy was required for detector stability. Dose-rate measurements were stable across a range from 0.26 to 15 Gy/min and dose response was linear, although the device overestimated small doses compared with pinpoint ionization chamber measurements. Output factors agreed with ionization chamber measurements to within 0.6% for square fields of side between 3 and 25 cm and within 1.2% for 2 x 2 cm(2) fields. The Octavius 4D phantom was found to be consistent with measurements made with radiochromic film, where the gantry angle was found to be within 0.4. of that expected during rotational deliveries. RapidArc FF and FFF beams were found to have an accuracy of >97.9% and >90% of pixels passing 3%/3 mm and 2%/2 mm, respectively. Detector spatial resolution was observed to be a factor in determining the accurate delivery of each plan, particularly at steep dose gradients. This was confirmed using data from a second detector array with higher spatial resolution and with radiochromic film.

Conclusions: The Octavius 4D phantom with associated Octavius detector 729 ionization chamber array is a dosimetrically and mechanically stable device for pretreatment verification of FF and FFF RapidArc treatments. Further improvements may be possible through use of a detector array with higher spatial resolution (detector size and/or detector spacing). (C) 2013 American Association of Physicists in Medicine.