Standard Radiation Dosimetry Models: What Interventional Radiologists Need to Know

Thoughtful and accurate dosimetry is critical to obtain the safest and most efficacious yttrium-90 (Y90) radioembolization of primary and secondary liver cancers. Three dosimetry models are currently used in clinical practice, namely, body surface area model, medical internal radiation dose model, and the partition model. The objective of this review is to briefly outline the history behind Y90 dosimetry and the difference between the aforementioned models. When applying these three models to a single case, the differences between them are further demonstrated. Each dosimetry model in clinical practice has its own benefits and limitations. Therefore, it is incumbent upon practicing interventional radiologists to be aware of these differences to optimize treatment outcomes for their patients.

In vitro Interactive Toxicity of Binary Mixtures of Selected Herbicides on Lysinibacillusfusiformis

Aims: To assess the toxicities of some herbicides as individuals and in binary mixtures to Lysinibacillus fusiformis isolated from Oryzasativa plant using dehydrogenase activity as an endpoint. Study Design: The binary mixture consists of combination of any two herbicides selected from the three herbicides (drysate, weedcut and aminoforce) for the study The binary mixture ratios (%) were designed as: 50%:50%; 80%:20% and 20%:80% for the respective mixtures in the concentration range of 0 -10, 000 mg/L. Place and Duration of Study: Silver Press Laboratory, Owerri Nigeria between July, 2016 and August, 2019. Methodology: A laboratory scale study was carried on three toxicants using dehydrogenase inhibition test. The inhibition of dehydrogenase activity of the isolate by toxicant was calculated relative to the control. All the dose-response relationships of the individual toxicants and that of themixtures were described by logistic dose model and Weibullcum model parameter. Results: The results revealed that the median inhibitory concentrations (IC50) observed were 1,067.33 ± 36.68 mg/L for drysate; 2,180.00 ± 147.31 mg/L for weedcut and 4,550.00 ± 62.45 mg/L for aminoforce. Duncan tests indicated that the IC50 of the toxicants were significantly different from each other. Among the individual toxicants, the ascending toxicities ranking were aminoforce > weedcut > drysate. The responses of the test organism to the stresses of the toxicants were dose-dependent and the toxicants also progressively repressed the dehydrogenase activity as the concentration increased. All binary mixtures were strongly synergistic against the organism. Conclusion: Thus, the toxicity of individual compound and synergistic effects of the mixtures of the toxicants indicates potential deleterious effects of both the individual chemicals and their mixtures to the rhizobacteria of Oryza sativa plant.

A relationship between the incremental values of area under the ROC curve and of area under the precision-recall curve

Background Incremental value (IncV) evaluates the performance change between an existing risk model and a new model. Different IncV metrics do not always agree with each other. For example, compared with a prescribed-dose model, an ovarian-dose model for predicting acute ovarian failure has a slightly lower area under the receiver operating characteristic curve (AUC) but increases the area under the precision-recall curve (AP) by 48%. This phenomenon of disagreement is not uncommon, and can create confusion when assessing whether the added information improves the model prediction accuracy. Methods In this article, we examine the analytical connections and differences between the AUC IncV (ΔAUC) and AP IncV (ΔAP). We also compare the true values of these two IncV metrics in a numerical study. Additionally, as both are semi-proper scoring rules, we compare them with a strictly proper scoring rule: the IncV of the scaled Brier score (ΔsBrS) in the numerical study. Results We demonstrate that ΔAUC and ΔAP are both weighted averages of the changes (from the existing model to the new one) in separating the risk score distributions between events and non-events. However, ΔAP assigns heavier weights to the changes in higher-risk regions, whereas ΔAUC weights the changes equally. Due to this difference, the two IncV metrics can disagree, and the numerical study shows that their disagreement becomes more pronounced as the event rate decreases. In the numerical study, we also find that ΔAP has a wide range, from negative to positive, but the range of ΔAUC is much smaller. In addition, ΔAP and ΔsBrS are highly consistent, but ΔAUC is negatively correlated with ΔsBrS and ΔAP when the event rate is low. Conclusions ΔAUC treats the wins and losses of a new risk model equally across different risk regions. When neither the existing or new model is the true model, this equality could attenuate a superior performance of the new model for a sub-region. In contrast, ΔAP accentuates the change in the prediction accuracy for higher-risk regions.

A new CEM₄₃ thermal dose model based on Vogel-Tammann-Fulcher behaviour in thermal damage processes

Thermal dose models are metrics that quantify thermal damage in tissues based on the temperature and the time of exposure. The validity and accuracy of one of the commonly used models (CEM₄₃) for high temperature thermal therapy applications (50-90 degree Celcius) is questionable. It was found to over-estimate the accumulation of thermal damage for high-temperature applications. A new CEM₄₃ dose model based on Arrhenius type Vogel-Tammann-Fulcher equation using published data is introduced in this work. The new dose values for the same damage threshold that was produced at different in-vivo skin experiments were in the same order of magnitude, while the current dose values were 2 orders of magnitude different. The new dose values for same damage threshold in 6 lessions in ex-vivo liver experiments were more consistent than the current dose values. Computer simulations of laser interstitial thermal therapy showed that the current model usually predicts bigger volume than the new model does. The deviation in damaged volume prediction can be significant. The contribution of this work is introducing methods that can lead to more robust thermal dosimetry which will result in improved therapy modelling, monitoring and control.

A new CEM₄₃ thermal dose model based on Vogel-Tammann-Fulcher behaviour in thermal damage processes

Thermal dose models are metrics that quantify thermal damage in tissues based on the temperature and the time of exposure. The validity and accuracy of one of the commonly used models (CEM₄₃) for high temperature thermal therapy applications (50-90 degree Celcius) is questionable. It was found to over-estimate the accumulation of thermal damage for high-temperature applications. A new CEM₄₃ dose model based on Arrhenius type Vogel-Tammann-Fulcher equation using published data is introduced in this work. The new dose values for the same damage threshold that was produced at different in-vivo skin experiments were in the same order of magnitude, while the current dose values were 2 orders of magnitude different. The new dose values for same damage threshold in 6 lessions in ex-vivo liver experiments were more consistent than the current dose values. Computer simulations of laser interstitial thermal therapy showed that the current model usually predicts bigger volume than the new model does. The deviation in damaged volume prediction can be significant. The contribution of this work is introducing methods that can lead to more robust thermal dosimetry which will result in improved therapy modelling, monitoring and control.

Uncertainty propagation from ensemble dispersion simulations through a terrestrial food chain and dose model

In the framework of the European project CONFIDENCE, Work Package 1 (WP1) focused on the uncertainties in the pre- and early phase of a radiological emergency. One subtask was to analyse the propagation of uncertainties from ensemble dispersion simulations through a terrestrial food chain and dose model. Uncertainties that may occur in the modelling of radioactivity in the food chain were added to previously defined meteorological and source term uncertainties. Endpoints of the ensemble calculations within the food chain model included activity concentrations in the food chain, i.e. feedstuffs and foodstuffs, as well as the internal dose through ingestion. This paper describes the uncertainty propagation through a terrestrial food chain and dose model and presents some illustrations of the results.