Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon beams.

An addendum to the AAPM's TG-51 protocol for the determination of absorbed dose to water in megavoltage photon beams is presented. This addendum continues the procedure laid out in TG-51 but new kQ data for photon beams, based on Monte Carlo simulations, are presented and recommendations are given to improve the accuracy and consistency of the protocol's implementation. The components of the uncertainty budget in determining absorbed dose to water at the reference point are introduced and the magnitude of each component discussed. Finally, the consistency of experimental determination of ND,w coefficients is discussed. It is expected that the implementation of this addendum will be straightforward, assuming that the user is already familiar with TG-51. The changes introduced by this report are generally minor, although new recommendations could result in procedural changes for individual users. It is expected that the effort on the medical physicist's part to implement this addendum will not be significant and could be done as part of the annual linac calibration.

New National Air-Kerma Standard for Low-Energy Electronic Brachytherapy Sources.

The new primary standard for low-energy electronic brachytherapy sources for the United States is described. These miniature x-ray tubes are inserted in catheters for interstitial radiation therapy and operate at tube potentials of up to about 50 kV. The standard is based on the realization of the air kerma produced by the x-ray beam at a reference distance in air of 50 cm.

Measurements and standards for bulk-explosives detection.

Recent years have seen a dramatic expansion in the application of radiation and isotopes to security screening. This has been driven primarily by increased incidents involving improvised explosive devices as well as their ease of assembly and leveraged disruption of transportation and commerce. With global expenditures for security-screening systems in the hundreds of billions of dollars, there is a pressing need to develop, apply, and harmonize standards for x-ray and gamma-ray screening systems used to detect explosives and other contraband. The National Institute of Standards and Technology has been facilitating the development of standard measurement tools that can be used to gauge the technical performance (imaging quality) and radiation safety of systems used to screen luggage, persons, vehicles, cargo, and left-behind objects. After a review of this new suite of national standard test methods, test objects, and radiation-measurement protocols, we highlight some of the technical trends that are enhancing the revision of baseline standards. Finally we advocate a more intentional use of technical-performance standards by security stakeholders and outline the advantages this would accrue.

Efficiency calibrations of cylindrically bent transmission crystals in the 20 to 80 keV x-ray energy range.

Two quartz (10-11) crystals were cylindrically bent to a 25.4 cm radius of curvature and were mounted in identical Cauchois-type transmission spectrometers, and the crystal diffraction efficiencies were measured to 5% absolute accuracy using narrow bandwidth x-ray source fluences in the 20 to 80 keV energy range. The measured integrated reflectivity values were compared to calculations performed using a computational model that accounts for the diffraction geometry of the bent transmission crystal. These crystal calibrations enable the accurate measurement of absolute hard x-ray emission levels from laser-produced plasmas and other laboratory sources.

Evaluation of the new cesium-131 seed for use in low-energy x-ray brachytherapy.

Characterization measurements and calculations were performed on a new medical seed developed by IsoRay Inc. in Richland, Washington, that utilizes the short-lived isotope 131Cs. This model has recently received FDA 510(k) clearance. The objective of this work was to characterize the dosimetric properties of the new seed according to the AAPM Task Group 43 recommendations. Cesium-131 is a low-energy x-ray emitter, with the most prominent peaks in the 29 keV to 34 keV region. The intended application is brachytherapy for treating cancers in prostate, breast, head and neck, lung, and pancreas. The evaluations performed included air-kerma strength, radial dose function, anisotropy in phantom, half-life, energy spectra, and internal activity. The results indicate the CS-1 seeds have a dose-rate constant of 0.915 cGy hr(-1) U(-1) in water, dose penetration characteristics similar to 125I and 103Pd, anisotropy function values on the order of 0.71 at short distances and small angles, and an average anisotropy factor of 0.964. The overall dosimetric characteristics are similar to 125I and 103Pd seeds with the exception of half-life, which is 9.7 days, as compared to 17 days for 103Pd and 60 days for 125I. The shorter half-life may offer significant advantages in biological effectiveness.

Erratum: New National Air-Kerma-Strength Standards for (125)I and (103)Pd Brachytherapy Seeds.

[This corrects the article on p. 337 in vol. 108.].

Dosimetry characterization of a 32P source wire used for intravascular brachytherapy with automated stepping.

Depth-dose curve measurements and Monte Carlo simulations for a catheter-based 32P intravascular brachytherapy source wire are described. The measured dose rates were obtained using both radiochromic-dye film and an extrapolation chamber (EC). Calibrated radiochromic-dye films were irradiated at distances between 0.5 and 5 mm from the source axis in polystyrene phantoms, and scanned with high-resolution densitometers. Measurements with an automated EC with a 1 mm diameter collecting electrode were also performed at a distance of 2 mm from the source in polystyrene. The measured dose rates obtained from the film and EC were divided by the measured source activity to obtain measured values of dose rate per unit contained activity. Dosimetric calculations of the catheter-based 32P wire geometry were also obtained using several Monte Carlo codes (CYLTRAN, MCNP, PENELOPE, and EGS). The measured and calculated values of dose rate per unit contained activity are in good agreement (<10%) within the relevant treatment distances (1 to 4 mm). With carefully selected input parameters, the calculated depth-dose curves using these codes were within 5% at 4 mm depth. At greater depths the discrepancies between the codes increase. We discuss likely mechanisms for these differences.

Changes in the U.S. Primary Standards for the Air Kerma From Gamma-Ray Beams.

Monte Carlo photon-electron transport calculations have been done to derive new wall corrections for the six NBS-NIST standard graphite-wall, air-ionization cavity chambers that serve as the U.S. national primary standard for air kerma (and exposure) for gamma rays from (60)Co, (137)Cs, and (192)Ir sources. The data developed for and from these calculations have also been used to refine a number of other factors affecting the standards. The largest changes are due to the new wall corrections, and the total changes are +0.87 % to +1.11 % (depending on the chamber) for (60)Co beams, +0.64 % to +1.07 % (depending on the chamber) for (137)Cs beams, and -0.06 % for the single chamber used in the measurement of the standardized (192)Ir source. The primary standards for air kerma will be adjusted in the near future to reflect the changes in factors described in this work.

New National Air-Kerma-Strength Standards for (125)I and (103)Pd Brachytherapy Seeds.

The new U.S. measurement standard for the air-kerma strength from low-energy photon-emitting brachytherapy seed sources is formally described in detail. This instrument-based standard was implemented on 1 January 1999, with its salient features and the implications of differences with the previous standard given only through a series of informal communications. The Wide-Angle Free-Air Chamber (WAFAC) is specially designed to realize air kerma from a single-seed source emitting photons with energies up to about 40 keV, and is now used to measure the wide variety of seeds used in prostate-cancer therapy that has appeared in the last few years. For the two (125)I seed models that have been subject to both the old and new standards, the new standard reduces the air-kerma strength by 10.3 %. This change is mainly due to the removal of the influence on the measurement of the Ti K x rays produced in the source encapsulation, a component with no clinical significance.

Radiation research society 1952-2002. Physics as an element of radiation research.

Since its inception in 1954, Radiation Research has published an estimated total of about 8700 scientific articles up to August 2001, about 520, or roughly 6%, of which are primarily related to physics. This average of about 11 articles per year indicates steadily continuing contributions by physicists, though there are appreciable fluctuations from year to year. These works of physicists concern radiation sources, dosimetry, instrumentation for measurements of radiation effects, fundamentals of radiation physics, mechanisms of radiation actions, and applications. In this review, we have selected some notable accomplishments for discussion and present an outlook for the future.