Research Spotlight

Garan, A.R., Kanwar, M., Thayer, K.L., Whitehead, E., Zweck, E., Hernandez-Montfort, J., Mahr, C., Haywood, J.L., Harwani, N.M., Wencker, D., Sinha, S.S., Vorovich, E., Abraham, J., O’Neill, W., Burkhoff, D. and Kapur, N.K. (2020). “Complete Hemodynamic Profiling With Pulmonary Artery Catheters in Cardiogenic Shock Is Associated With Lower In-Hospital Mortality.” JACC Heart Fail 8(11): 903-913.

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OBJECTIVES: The purpose of this study was to investigate the association between obtaining hemodynamic data from early pulmonary artery catheter (PAC) placement and outcomes in cardiogenic shock (CS). BACKGROUND: Although PACs are used to guide CS management decisions, evidence supporting their optimal use in CS is lacking. METHODS: The Cardiogenic Shock Working Group (CSWG) collected retrospective data in CS patients from 8 tertiary care institutions from 2016 to 2019. Patients were divided by Society for Cardiovascular Angiography and Interventions (SCAI) stages and outcomes analyzed by the PAC-use group (no PAC data, incomplete PAC data, complete PAC data) prior to initiating mechanical circulatory support (MCS). RESULTS: Of 1,414 patients with CS analyzed, 1,025 (72.5%) were male, and 494 (34.9%) presented with myocardial infarction; 758 (53.6%) were in SCAI Stage D shock, and 263 (18.6%) were in Stage C shock. Temporary MCS devices were used in 1,190 (84%) of those in advanced CS stages. PAC data were not obtained in 216 patients (18%) prior to MCS, whereas 598 patients (42%) had complete hemodynamic data. Mortality differed significantly between PAC-use groups within the overall cohort (p < 0.001), and each SCAI Stage subcohort (Stage C: p = 0.03; Stage D: p = 0.05; Stage E: p = 0.02). The complete PAC assessment group had the lowest in-hospital mortality than the other groups across all SCAI stages. Having no PAC assessment was associated with higher in-hospital mortality than complete PAC assessment in the overall cohort (adjusted odds ratio: 1.57; 95% confidence interval: 1.06 to 2.33). CONCLUSIONS: The CSWG is a large multicenter registry representing real-world patients with CS in the contemporary MCS era. Use of complete PAC-derived hemodynamic data prior to MCS initiation is associated with improved survival from CS.

Weir, V.J. and Zhang, J. (2020). “A polynomial approximation to an exponential growth function for calculating equilibrium dose in CT.” Phys Med Biol 65(20): 20nt01.

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We propose a polynomial approach to approximate equilibrium dose [Formula: see text] reported in AAPM TG111 method of wide beam CT dosimetry. A formula for [Formula: see text] was derived by expanding the exponential growth function in a Taylor series and comparing the resulting function to a polynomial. The formula incorporates coefficients of polynomial fits up to 3rd order. The polynomial coefficients were obtained as fits of the point dose data and used to calculate the length constant β and [Formula: see text] The length constant could also be made available to users by the vendors of various makes and models of CT scanners. We evaluated our polynomial approximation formula for [Formula: see text] by comparing with [Formula: see text] obtained from measured data in a 256 slice GE revolution CT scanner. To that end, point dose data was collected in 600 mm body and head phantoms with a Farmer chamber for beam widths from 40 to 160 mm. A table of [Formula: see text] and length constants β, and plots of fits for various filters (pediatric head, adult head, large body, medium body and small body bowtie filters) were presented. For the 256 slice GE revolution CT scanner, a length constant of [Formula: see text] can be used for pediatric head, adult head, body (large filter), body (medium filter), and body (small filter) at 120 kV when growth function fit is used. The estimated [Formula: see text] using the proposed polynomial based method is within 86.79% (83.14%-90.38%) of [Formula: see text] obtained from fitting the growth function for beam widths from 40 to 160 mm. The proposed polynomial based estimation to the equilibrium dose, [Formula: see text] can be readily implemented in practice for point dose measurements of wide beam CT scanners.

Schwarz, B.C., Godwin, W.J., Wayson, M.B., Dewji, S.A., Jokisch, D.W., Lee, C. and Bolch, W.E. (2020). “Specific absorbed fractions for a revised series of the UF/NCI pediatric reference phantoms: internal photon sources.” Phys Med Biol Nov 3. [Epub ahead of print].

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Assessment of radiation absorbed dose to internal organs of the body from the intake of radionuclides or, in the medical setting through the injection of radiopharmaceuticals, is generally performed based upon reference biokinetic models or patient imaging data, respectively. Biokinetic models estimate the time course of activity localized to source organs. The time-integration of these organ activity profiles are then scaled by the radionuclide S value, which defines the absorbed dose to a target tissue per nuclear transformation in various source tissues. S values are computed using established nuclear decay information (particle energies and yields), and a parameter termed the specific absorbed fraction (SAF). The SAF is the ratio of the absorbed fraction (AF) – fraction of particle energy emitted in the source tissue that is deposited in the target tissue – and the target organ mass. While values of the SAF may be computed using patient-specific or individual-specific anatomic models, they have been more widely available through the use of computational reference phantoms. In this study, we report on an extensive series of photon SAFs computed in a revised series of the UF/NCI pediatric reference phantoms which have been modified to conform to the specifications embodied in the ICRP reference adult phantoms of Publication 110 (e.g., organs modeled, organ ID numbers, blood contribution to elemental compositions). Following phantom anatomical revisions, photon radiation transport simulations were performed using MCNPX v2.7 in each of the 10 phantoms of the series – male and female newborn, 1-year-old, 5-year-old, 10-year-old, and 15-year-old – for 44 different source and target tissues. A total of 25 photon energies were considered from 10 keV to 10 MeV along a logarithm energy grid. Detailed analyses were conducted of the relative statistical errors in the Monte Carlo target tissue energy deposition tallies at low photon energies and over all energies for source-target combinations at large intra-organ separation distances. Based on these analyses, various data smoothing algorithms were employed, including multi-point weighted data smoothing, and log-log interpolation at low energies (1 and 5 keV) using limiting SAF values based upon target organ mass to bound the interpolation interval. The final dataset is provided in a series of 10 electronic annexes in MS Excel format. The results of this study were further used as the basis for assessing the radiative component of internal electron source SAFs as described in our companion paper for this same pediatric phantom series.

Schwarz, B.C., Godwin, W.J., Wayson, M.B., Dewji, S.A., Jokisch, D.W., Lee, C. and Bolch, W.E. (2020). “Specific absorbed fractions for a revised series of the UF/NCI pediatric reference phantoms: internal electron sources.” Phys Med Biol Nov 3. [Epub ahead of print].

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In both the ICRP and MIRD schemata of internal dosimetry, the S-value is defined as the absorbed dose to a target organ per nuclear decay of the radionuclide in a source organ. Its computation requires data on the energies and yields of all radiation emissions from radionuclide decay, the mass of the target organ, and the value of the absorbed fraction – the fraction of particle energy emitted in the source organ that is deposited in the target organ. The specific absorbed fraction (SAF) is given as the ratio of the absorbed fraction and the target mass. Historically, in the early development of both schemata, computational simplifications were made to the absorbed fraction in considering both organ self-dose (r_S=r_T) and organ cross-dose (r_S≠r_T). In particular, the value of the absorbed fraction was set to unity for all “non-penetrating” particle emissions (electrons and alpha particles) such that they contributed only to organ self-dose. As radiation transport codes for charged particles became more widely available, it became increasingly possible to abandon this distinction and to explicitly consider the transport of internally emitted electrons in a manner analogous to that for photons. In this present study, we report on an extensive series of electron SAFs computed in a revised series of the UF/NCI pediatric phantoms. A total of 28 electron energies – 0 to 10 MeV – along a logarithmic energy grid are provided in electronic annexes, where 0 keV is associated with limiting values of the SAF. Electron SAFs were computed independently for collisional energy losses (SAFCEL) and radiation energy losses (SAFREL) to the target organ. A methodology was employed in which values of SAFREL were compiled by first assembling organ-specific and electron energy-specific bremsstrahlung x-ray spectra, and then using these x-ray spectra to re-weight a previously established monoenergetic database of photon SAFs for all phantoms and source-target combinations. Age-dependent trends in the electron SAF were demonstrated for the majority of the source-target organ pairs, and were consistent to values given for the ICRP adult phantoms. In selected cases, however, anticipated age-dependent trends were not seen, and were attributed to anatomical differences in relative organ positioning at specific phantom ages. Both the electron SAFs of this study, and the photon SAFs from our companion study, are presently being used by ICRP Committee 2 in its upcoming pediatric extension to ICRP Publication 133.

Curcio, N., Bennett, M.M., Hebeler, K.R., Warren, A.M. and Edgerton, J.R. (2020). “Quality of Life Is Improved One Year Following Cardiac Surgery.” Ann Thorac Surg Oct 13;S0003-4975(20)31658-1. [Epub ahead of print].

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BACKGROUND: Quality of life (QoL) is increasingly important in the era of patient-centered outcomes and value-based reimbursement. However, most follow-up is limited to 30 days and long-term data on QoL improvement associated with symptom relief are lacking. Therefore, we sought to analyze QoL following cardiac surgery in a non-emergent, all-comers population. METHODS: A total of 402 patients undergoing routine cardiac surgery at two large urban hospitals in the Dallas, Texas area were enrolled. Follow-up was complete for 364 patients. Data was collected from 08/2013-01/2017. The Kansas City Cardiomyopathy Questionnaire (KCCQ) was administered at baseline, one month, and one year following surgery. Repeated measures analysis was used for each domain of the KCCQ for all procedures and stratified by procedure. If time was found to be a significant factor, pairwise analysis was performed with p-values adjusted using Tukey-Kramer method. RESULTS: There was a significant increase across all domains of KCCQ scores for all procedures and for most domains when stratifying by procedure. This increase in QoL is most marked after one month. All domain scores increased through one year except symptom stability which peaked at one month post-surgery and then regressed at one year, suggesting an overall improvement and stabilization of symptoms. The occurrence of complications did not alter this trajectory. CONCLUSIONS: QoL and other patient-centered outcomes are improved at one month and continue to improve throughout the year. Knowledge of these data is important for patient selection, fully informed consent and shared decision making.