SPIO-enhanced MR imaging with proton-density-weighted or FLASH sequences was more accurate in the detection of small HCCs in cirrhotic livers.

A fully automatic radiophotoluminescent glass rod dosimeter (GRD) system has recently become commercially available. This article discusses the dosimetric properties of the GRD including uniformity and reproducibility of signal, dose linearity, and energy and directional dependence in high-energy photon beams. In addition, energy response is measured in electron beams. The uniformity and reproducibility of the signal from 50 GRDs using a 60Co beam are both +/- 1.1% (one standard deviation). Good dose linearity of the GRD is maintained for doses ranging from 0.5 to 30 Gy, the lower and upper limits of this study, respectively. The GRD response is found to show little energy dependence in photon energies of a 60Co beam, 4 MV (TPR20(10)=0.617) and 10 MV (TPR(20)10=0.744) x-ray beams. However, the GRD responses for 9 MeV (mean energy, Ez = 3.6 MeV) and 16 MeV (Ez = 10.4 MeV) electron beams are 4%-5% lower than that for a 60Co beam in the beam quality dependence. The measured angular dependence of GRD, ranging from 0 degrees (along the long axis of GRD) to 120 degrees is within 1.5% for a 4 MV x-ray beam. As applications, a linear accelerator-based radiosurgery system and Cyber-Knife output factors are measured by a GRD and compared with those from various detectors including a p-type silicon diode detector, a diamond detector, and an ion chamber. It is found that the GRD is a very useful detector for small field dosimetry, in particular, below 10 mm circular fields.

Observer performance tests were conducted to compare the effects of image-processing technique (unsharp mask filtering) on the diagnostic accuracy of computed radiography (CR) with storage phosphors in the detection of microcalcifications. Comparison of detectability of microcalcifications with CR and with screen-film mammography was also performed. Clusters of microcalcifications (125-250 microns in diameter) were randomly superimposed on human breast specimens. Observer performance tests were carried out with receiver operating characteristic (ROC) analysis. The area under the ROC curve and the cumulative true-positive-localization fraction were both used as indexes of performance. Observer performance experiments with nine observers indicated that the two types of screen-film images used provided higher detectability than the CR images. The detectability of microcalcifications on the CR images improved slightly with use of the unsharp masking technique. However, no statistically significant difference was found between processed and unprocessed CR images, and detectability still did not reach the level achieved with the screen-film images.

We have recently developed a prototypical radiophotoluminescent glass plate dosimeter (GPD) system as a device for small field dosimetry. The purpose of this study is to examine the usefulness of the GPD system for small field dosimetry. The profiles measured with the GPD were evaluated by comparing them to those from Kodak X-Omat V and GAFCROMIC XR type R film dosimeters for 2, 5, 9, and 15 mm circular collimators created by a linear accelerator-based radiosurgery system. The GPD output factors were compared with those of various detectors including an ion chamber, a p-type silicon diode detector, a glass rod dosimeter (GRD), and a diamond detector. The results measured with the GPD were also confirmed by comparing them to those from Monte Carlo simulations. The accuracy of a simulated beam is validated by the excellent agreement between Monte Carlo calculated and measured central axis depth-dose curves for 9- and 15 mm circular collimators using 4- and 10 MV photon beams. The GPD profiles show almost the same full width at half maximum as those of film dosimeters and Monte Carlo simulations at 4- and 10 MV photon beams, but a little narrower penumbrae than the film dosimeters and Monte Carlo simulations. The output factors measured with the GPD are in good agreement with those from a diode detector, a diamond detector, and the GRD with a small active volume and Monte Carlo simulations, except for a very small 2 mm circular collimator. It was found that the GPD is a very useful detector for small field dosimetry.

We have developed a simple method for dose calculation in dual asymmetric open and irregular fields with four independent jaws and multileaf collimators. Our calculation method extends the scatter correction method of Kwa et al. [Med. Phys. 21, 1599-1604 (1994)] based on the principle of Day's equivalent-field calculation. The scatter correction factor was determined by the ratio of the derived doses of a smaller asymmetric open field or irregular field to a larger symmetric field. The algorithm with the scatter correction method can be calculated from output factors, tissue maximum ratios, and off-axis ratios for conventional symmetric fields. The doses calculated by this method were compared with the measured doses for various asymmetric open and irregular fields. The agreement between the calculated and measured doses for 4 and 10 MV photon beams was within 0.5% at the geometric center of the asymmetric open fields. For the asymmetric irregular fields with the same geometrical center, agreement within 1% was found in most cases.