Benchmark Dose analysis

The Benchmark dose (BMD) approach is a scientifically more advanced method compared to the No Observed Adverse Effect Level (NOAEL) approach for deriving a Reference Point (Point of Departure) for risk assessment (EFSA, 2017). The BMD method pre-defines a specific effect size, referred to as the Benchmark response (BMR) and estimates the dose (BMD) associated with the specified effect. The BMD is estimated from the complete dose‑response dataset by fitting dose-response models. Statistical uncertainties in the data are taken into account in the confidence interval around the BMD, the lower limit of which (denoted as BMDL) is the Point of Departure (or Reference Point) for deriving exposure limits.

Key elements of PROAST

PROAST can be applied to:

• dose-response data from all sorts of in vivo studies (animal, human or eco-toxicological)
• concentration-response data from in vitro studies
• high throughput data (e.g. gene expression as a function of dose)
• dose-response data from mixture studies
• combined dose-response datasets for similar endpoints in a single analysis
• non-linear regression in any other field of science, including the option to compare the relationships among subgroups
• the complete data from a toxicological study, by performing a quick (automated) analysis of a whole series of endpoints in a single run.
• decreasing residual concentrations in milk (or other animal products/tissues) for which repeated measurements in individuals are available.

An important feature of PROAST is that it allows for comparing dose-responses among various subgroups, e.g. among sexes, among study durations, or among replicate studies. Based on statistical analysis, PROAST indicates if the various dose-response relationships differ among the subgroups, and if so, in what sense (e.g. in background response, in sensitivity to the chemical, or in dose-response shape).

PROAST platforms

PROAST is developed in the computer language R. To facilitate its use, a web application is available, which does not require any knowledge of R. The web application is easy to use and covers standard dose-response analyses. For more specific goals, the R version of PROAST may be needed. The R version has the additional advantage that it can be run on your own machine (even off line), while it is easier to store your results. Below, some additional information is given on the various options to run PROAST. In case you have problems or questions, you may contact proast@rivm.nl.

PROAST as a web application

There are two web applications of PROAST available, either of which may be particularly useful if you want to quickly apply PROAST, avoiding the installation of software on your computer. These web applications are easy to apply, but do not include all functionalities of the R package of PROAST (see below). However, the usual dose-response analyses of toxicity data can be done in these web tools. The URLs are:

• https://efsa.openanalytics.eu/ for the EFSA web application
• https://proastweb.rivm.nl/ for the RIVM web application

For the first URL you need to create an account, the second URL can be used without an account. A manual for the first application can be found on the website itself (see “about” in the upper right corner). For the second web application, see PROAST MANUAL WebApp.pdf. 

Either web application will probably satisfy infrequent users of PROAST. However, if you use PROAST on a more regular basis, the stand alone R version of PROAST may be more convenient, making it worthwhile to put some effort in getting acquainted with working in R. Furthermore, not all options in PROAST have been implemented in the current web applications.
 
The two web applications above differ in one aspect: the PROAST web application (proastweb.rivm.nl) includes a special functionality:  the calculation of withdrawal periods based on monitored concentrations in individual animals over time (e.g. in cow’s milk). See Manual web application MILKINGS.

PROAST as an R package

PROAST can be run on your own machine as a package within R, which is a general statistical software environment, freely downloadable (https://cran.r-project.org/). Note that RStudio does not support all the R functions used by PROAST, so you need to run PROAST directly in R.

To install the PROAST package (copyright RIVM) on your computer, download the R package proast71.1.zip (using save as; do not unzip!) to your computer. Save the package at a convenient location in your folder system. In the top menu in R, click on “packages” and next on “Install package(s) from local zip files” Consult the PROAST manual (PROAST MANUAL menu version.pdf) to see how to perform an analysis using PROAST in R.

PROAST Versions

Since PROAST is an R package, it is relatively easy to make a new version available after fixing any bugs in the software code. After any change in the code, the PROAST package receives another version number, whether it relates to a small change (e.g., fixed bug) or a relatively large change (e.g., change in methodological approach due to updated guidance). In this way, outcomes from analyses in the past that differ from those in the present may be checked to be due to a another PROAST version being used, and if so, whether this relates to a bug, or to a different default setting, or to a change in methods used. In general, however, the outcomes from different PROAST versions will be similar (although more significant differences may occur before and after version 62.0, due to changes in EFSA guidance in 2017).

It is recommended to save all PROAST versions that you ever used (i.e. the zip or tgz file), preferably in a special folder on your computer, so that you can always reproduce calculations that were done in the past. Also, you will need the zip (or tgz) file when you install a new R version. If you find that outcomes differ when using a newer PROAST version for the same analysis, and are unable find the cause, you may contact proast@rivm.nl.

Calculation of withdrawal period for residuals in milk

The RIVM web application of PROAST can also be used for the calculation of the withdrawal period of cow’s milk needed for residue levels to have reached a sufficiently low level to make it save for consumption. When the residue data relate to cow’s with different dry off periods, the withdrawal period is calculated in dependence of the dry off period. For more information, see the manual under the help button in the RIVM web application of PROAST.

Updates or questions

If you are interested to be informed about updates of PROAST or other relevant information, send an e-mail to proast@rivm.nl. You can also use this email address to ask questions, or report bugs or weaknesses in the software. We will try to answer questions on the use of PROAST to the extent possible. 

Exercises

The folder PROAST exercises contains various computer exercises for the BMD analysis, if you want to further train you skills in dose-response modelling. Answers to the exercises can be found in answers.doc.

Further reading

A concise discussion of the BMD approach can be found in EFSA (2017). See Slob and Setzer (2014; Crit Rev Toxicol 44, 270-297) as an example of the use of PROAST in a more advanced setting, including dose-response analysis with covariates.  The Bo Holmstedt Award Lecture by Wout Slob (recorded as an mp4 video) provides a more fundamental critique on current toxicological principles and concepts, including the NOAEL. This lecture may be helpful in understanding why it is needed to change from NOAEL to BMD. Seedownloads on top of this page. (If you have difficulties in understanding the video due to visual or hearing impairment, you may contact proast@rivm.nl).

Bo Holmstedt Award lecture by Wout Slob