Quantification of internal dosimetry in PET patients II: Individualized Monte Carlo-based dosimetry for [18F]fluorocholine PET.

PURPOSE: To obtain individualized internal doses with a Monte Carlo (MC) method in patients undergoing diagnostic [18F]FCH-PET studies and to compare such doses with the MIRD method calculations. METHODS: A patient cohort of 17 males were imaged after intravenous administration of a mean [18F]FCH activity of 244.3 MBq. The resulting PET/CT images were processed in order to generate individualized input source and geometry files for dose computation with the MC tool GATE. The resulting dose estimates were studied and compared to the MIRD method with two different computational phantoms. Mass correction of the S-factors was applied when possible. Potential sources of uncertainty were closely examined: the effect of partial body images, urinary bladder emptying, and biokinetic modeling. RESULTS: Large differences in doses between our methodology and the MIRD method were found, generally in the range ±25%, and up to ±120% for some cases. The mass scaling showed improvements, especially for non-walled and high-uptake tissues. Simulations of the urinary bladder emptying showed negligible effects on doses to other organs, with the exception of the prostate. Dosimetry based on partial PET/CT images (excluding the legs) resulted in an overestimation of mean doses to bone, skin, and remaining tissues, and minor differences in other organs/tissues. Estimated uncertainties associated with the biokinetics of FCH introduce variations of cumulated activities in the range of ±10% in the high-uptake organs. CONCLUSIONS: The MC methodology allows for a higher degree of dosimetry individualization than the MIRD methodology, which in some cases leads to important differences in dose values. Dosimetry of FCH-PET based on a single partial PET study seems viable due to the particular biokinetics of FCH, even though some correction factors may need to be applied to estimate mean skin/bone doses.

Quantification of internal dosimetry in PET patients: individualized Monte Carlo vs generic phantom-based calculations.

PURPOSE: The purpose of this work is to calculate individualized dose distributions in patients undergoing 18 F-FDG PET/CT studies through a methodology based on full Monte Carlo (MC) simulations and PET/CT patient images, and to compare such values with those obtained by employing nonindividualized phantom-based methods. METHODS: We developed a MC-based methodology for individualized internal dose calculations, which relies on CT images (for organ segmentation and dose deposition), PET images (for organ segmentation and distributions of activities), and a biokinetic model (which works with information provided by PET and CT images) to obtain cumulated activities. The software vGATE version 8.1. was employed to carry out the Monte Carlo calculations. We also calculated deposited doses with nonindividualized phantom-based methods (Cristy-Eckerman, Stabin, and ICRP-133). RESULTS: Median MC-calculated dose/activity values are within 0.01-0.03 mGy/MBq for most organs, with higher doses delivered especially to the bladder wall, major vessels, and brain (medians of 0.058, 0.060, 0.066 mGy/MBq, respectively). Comparison with values obtained with nonindividualized phantom-based methods has shown important differences in many cases (ranging from -80% to + 260%). These differences are significant (p < 0.05) for several organs/tissues, namely, remaining tissues, adrenals, bladder wall, bones, upper large intestine, heart, pancreas, skin, and stomach wall. CONCLUSIONS: The methodology presented in this work is a viable and useful method to calculate internal dose distributions in patients undergoing medical procedures involving radiopharmaceuticals, individually, with higher accuracy than phantom-based methods, fulfilling the guidelines provided by the European Council directive 2013/59/Euratom.

[Real time myocardial contrast echocardiography to predict left ventricular wall motion recovery after reperfused acute myocardial infarction]. / Ecocardiografía de perfusión miocárdica en tiempo real para la predicción de la recuperación de la función ventricular después del infarto agudo de miocardio reperfundido.

INTRODUCTION AND OBJECTIVES: Real time myocardial contrast echocardiography (RTMCE) is a recently developed method. We sought to determine: a) whether RTMCE predicts recovery of left ventricular function after acute myocardial infarction (AMI), and b) whether data obtained with this method are comparable to those obtained with 99mTc-sestamibi single photon emission computed tomography (SPECT) and magnetic resonance. PATIENTS AND METHOD: We studied 85 patients with AMI who underwent angioplasty. RTMCE was performed 7 (4) days after AMI. Two-dimensional echocardiography was performed at the time of the RTMCE study and at follow-up (10 [4] weeks). SPECT and magnetic resonance were performed after AMI in 18 and 32 patients, respectively. RESULTS: Follow-up two-dimensional echocardiography results were available for 82 patients, who were subdivided into 2 groups: recovery (n=49) and no recovery (n=33). Regional (AMI-related) wall motion score index improved from 1.75 (0.49) to 1.32 (0.36) (P< .001) in the recovery group, and worsened from 1.85 (0.39) to 1.95 (0.36) in the no recovery group (P< .001). RTMCE perfusion score was 0.8 (0.3) in the recovery group, and 0.6 (0.4) in the no recovery group (P< .001). Concordance between RTMCE and SPECT in a segmental analysis was 78% (P< .001; kappa=0.49), whereas concordance between RTMCE and hyperenhancement with delayed contrast magnetic resonance findings was 70% (P< .001; kappa =0.35). Independent predictors of recovery were peak creatine kinase (OR=1.4 per 1000 UI; 95% CI, 1.0-1.9; P< .05) and RTMCE score (OR=8.8; 95% CI, 1.9-39.3; P< .01). A RTMCE score > or = 0.60 had a positive predictive value of 73% and a negative predictive value of 69% (P< .001; area under the curve 0.70). CONCLUSION: RTMCE showed a modest predictive value for recovery of left ventricular function after reperfused AMI.

Ecocardiografía de perfusión miocárdica en tiempo real para la predicción de la recuperación de la función ventricular después del infarto agudo de miocardio reperfundido / Real time myocardial contrast echocardiography to predict left ventricular wall motion recovery after reperfused acute myocardial infarction

Introducción y objetivos. La ecocardiografía de perfusión en tiempo real (EPTR) es un método reciente. Los objetivos fueron estudiar: a) si la EPTR predice la recuperación después de infarto agudo de miocardio (IAM), y b) si los datos son comparables a los obtenidos con la tomografía computarizada por emisión de fotones simples (SPECT) marcada con 99m Tc-sestamibi y la resonancia magnética (RM). Pacientes y método. Hemos incluido a 85 pacientes con IAM sometidos a angioplastia coronaria transluminal percutánea (ACTP). La EPTR se realizó 7 ñ 4 días después del IAM. Se utilizó ecocardiografía a la vez que la perfusión y a las 10 ñ 4 semanas de ésta. La SPECT y la RM se realizaron después del IAM en 18 y 32 pacientes, respectivamente. Resultados. Al finalizar el seguimiento dispusimos de ecocardiografía de 82 pacientes, a los que dividimos en: grupo con recuperación (GR) (n = 49) y grupo sin recuperación (GNR) (n = 33). El índice de motilidad segmentaria (IMS) regional mejoró desde 1,75 ñ 0,49 a 1,32 ñ 0,36 (p < 0,001) en el GR, y empeoró desde 1,85 ñ 0,39 a 1,95 ñ 0,36 en el GNR (p < 0,001). El índice de EPTR era de 0,8 ñ 0,3 en el GR y de 0,6 ñ 0,4 en el GNR (p < 0,001). La concordancia entre la EPTR y la SPECT en un análisis segmentario era del 78 por ciento (p < 0,001; k= 0,49), y entre la EPTR y el hipercontraste tardío de la RM era del 70 por ciento (p < 0,001;k = 0,35). Los predictores independientes de recuperación fueron el valor de la creatincinasa (odds ratio [OR] = 1,4 por cada 1.000 U; intervalo de confianza [IC] del 95 por ciento, 1,0-1,9; p < 0,05) y el índice de EPTR (OR = 8,8; IC del 95 por ciento, 1,9-39,3; p < 0,01). Un índice 0,60 tuvo un valor predictivo positivo del 73 por ciento y negativo del 69 por ciento (p < 0,001; ABC = 0,70).Conclusión. La EPTR tiene valor moderado para predecir la recuperación funcional después del IAM reperfundido (AU)