Regulatory evaluation of prostate volume implants: pitfalls of a retrospective assessment.
ABSTRACT Evaluate for regulatory compliance the prostate implants from the Philadelphia Veterans Medical Center applying both an activity-based and volume-corrected D(90) (the maximum dose delivered to 90% of the prostate volume) metrics.
Dosimetry from 107 prostate implants performed at the Philadelphia Veterans Medical Center used immediate postprocedural CT image sets. D(90) values were adjusted for volume differences from planning volumes. Medical events (MEs) determined from the volume-corrected data were compared with an activity-based metric.
Examination of images using original and third-party reviewed prostate contours revealed 56 and 62 cases with D(90) values <80% of the prescription dose, respectively. Because postprocedural prostate volumes were on average 55.7% larger than the planned volume, clinical nomogram-based doses using the implanted activity and actual volumes found 34-47 implants failing to achieve doses greater than 80% of the prescription dose. Volume correction identified 20 MEs, 9 cases with D(90) values within 4% of the ME threshold and 11 significantly inferior cases with median D(90) values <52% of the prescribed dose. Eleven implants also had 20% or more seeds beyond the treatment site according to an activity metric recommended by the VHA Blue Ribbon Panel. Ten of these 11 cases were also identified by volume-corrected D(90) metric. The remaining 96 cases, however, had 95% (±6%) of seeds placed within the treatment site.
Of the cases reported to the United States Nuclear Regulatory Commission (NRC) on the basis of Day-1 D(90) values, many appear to have been acceptable implants relative to standard-of-practice clinical criteria. The activity-based dose metric, endorsed by the NRC Advisory Committee on the Medical Uses of Isotopes in 2005 and recommended by the VHA Blue Ribbon Panel for Prostate Brachytherapy yields a more robust determination of ME for this population of implants.
- SourceAvailable from: psu.edu
Conference Proceeding: Reducing cache misses by application-specific re-configurable indexing[show abstract] [hide abstract]
ABSTRACT: The predictability of memory access patterns in embedded systems can be successfully exploited to devise effective application-specific cache optimizations. In this work, we propose an improved indexing scheme for direct-mapped caches, which drastically reduces the number of conflict misses by using application-specific information; the scheme is based on the selection of a subset of the address bits. With respect to similar approaches, our solution has two main strengths. First, it models the misses analytically by building a miss equation, and exploits a symbolic algorithm to compute the exact optimum solution (i.e., the subset of address bits to be used as cache index that minimizes conflict misses). Second, we designed a re-configurable bit selector, which can be programmed at run-time to fit the optimal cache indexing to a given application. Results show an average reduction of conflict misses of 24%, measured over a set of standard benchmarks, and for different cache configurations.Computer Aided Design, 2004. ICCAD-2004. IEEE/ACM International Conference on; 12/2004