Report of AAPM Therapy Physics Committee Task Group 74: Inâ air output ratio, Sc, for megavoltage photon beams

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134830/1/mp7367.pd

Current measures of metabolic heterogeneity within cervical cancer do not predict disease outcome

<p>Abstract</p> <p>Background</p> <p>A previous study evaluated the intra-tumoral heterogeneity observed in the uptake of F-18 fluorodeoxyglucose (FDG) in pre-treatment positron emission tomography (PET) scans of cancers of the uterine cervix as an indicator of disease outcome. This was done via a novel statistic which ostensibly measured the spatial variations in intra-tumoral metabolic activity. In this work, we argue that statistic is intrinsically <it>non</it>-spatial, and that the apparent delineation between unsuccessfully- and successfully-treated patient groups via that statistic is spurious.</p> <p>Methods</p> <p>We first offer a straightforward mathematical demonstration of our argument. Next, we recapitulate an assiduous re-analysis of the originally published data which was derived from FDG-PET imagery. Finally, we present the results of a principal component analysis of FDG-PET images similar to those previously analyzed.</p> <p>Results</p> <p>We find that the previously published measure of intra-tumoral heterogeneity is intrinsically non-spatial, and actually is only a surrogate for tumor volume. We also find that an optimized linear combination of more canonical heterogeneity quantifiers does not predict disease outcome.</p> <p>Conclusions</p> <p>Current measures of intra-tumoral metabolic activity are not predictive of disease outcome as has been claimed previously. The implications of this finding are: clinical categorization of patients based upon these statistics is invalid; more sophisticated, and perhaps innately-geometric, quantifications of metabolic activity are required for predicting disease outcome.</p

Competition, prices and quality in the market for physician consultations

Prices for consultations with General Practitioners (GP's) in Australia are unregulated, and patients pay the difference between the price set by the GP and a fixed reimbursement from the national tax-funded Medicare insurance scheme. We construct a Vickrey-Salop model of GP price and quality competition and test its predictions using individual GP-level data on prices, the proportion of patients who are charged no out-of-pocket fee, average consultation length, and characteristics of the GP's, their practices and their local areas. We measure the competition to which the GP is exposed by the distance to other GP practices and allow for the endogeneity of GP location decisions with measures of area characteristics and area fixed-effects. Within areas, GP's with more distant competitors charge higher prices and a smaller proportion of their patients make no out-of-pocket payment. GP's with more distant competitors also have shorter consultations, though the effect is small and statistically insignificant

Firm Types, Price-setting Strategies, and Consumption-tax Incidence

Studying very detailed micro data collected around two different VAT reforms in Europe, we show that tax incidence is heavily dependent on the characteristics of the price-setting firms. The reforms generated bimodal price-change distributions; nearly all independent restaurants left prices unchanged whereas a substantial fraction of restaurants belonging to chains chose a complete pass-through. These differences cannot be explained by location, initial prices or other market-segment indicators. Instead, differences appear to arise because independent restaurants aim for (very) crude price ranges rather than fine-tuned optimized prices, whereas chains use more elaborate, coordinated pricing strategies

Development and characterization of a handheld radiation detector for radio-guided surgery

WOS:000543414900004The current state-of-the-art breast surgery uses radioactive brachytherapy sources to indicate the center of the tumor and possibly a few points on the periphery as seen on mammography. Since such guidance is very coarse, tumor free margins are not achievable in many cases and a re-excision procedure is often required. Better radiation guidance (radio-guidance) could come from labelling cancer cells directly with a radionuclide, such as the agent CLR1404. The agent CLR1404 is taken up by breast cancer cells but not normal cells and, labelled with radioactive I-123, could image the whole tumor, not just points. Tc-99m-labelled nanoparticles are used to locate sentinel lymph nodes. Simultaneous detection and differentiation of the photon energies 159 keV from I-123 and 141 keV from Tc-99m requires a radiation detector with high energy resolution and sufficient efficiency. This report involves the design, development and characterization of such a handheld radiation detector. Following the design and integration of the detector, the main characteristics of the detector, such as energy resolution, photopeak efficiency and response at different source-to-detector distances were investigated experimentally. Energy resolution of the detector was found to be less than 10 keV (FWHM) at energies below 159 keV, which allowed discerning the radiation from the two radionuclides. Energy spectra of the radioactive sources acquired experimentally were compared to those simulated in Monte Carlo N-Particle Transport Code (MCNP6X). The detector developed was found to be promising for radiation-guided surgery applications.The authors thank M.R. Farukhi, Ph. D and Zaid Farukhi from Rexon Components & TLD systems Inc. (Cleveland, OH) for assistance with the integration of the handheld radiation detector unit. Funding for this research was provided by the Turkish Ministry of Education under the YLSY grant program; The Department of Radiology at the University of Wisconsin-Madison under the R&D pilot funding program [Grant: 1804-003], The Department of Human Oncology at the University of Wisconsin-Madison under the Discretionary Research Funding Program, Principle Investigator [Grant: 233-KK30].