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Consider a stacked bar chart on its side. The researchers were fortunate in that the sequence is always the same (multi-agent always follows single agent), no therapies repeat, and there were no breaks between therapies for any patient. You will need a calculated field to determine days, and charting that instead of dates will align the various starts for easy comparison. Negative values for days are used to achieve the "before day zero" part of the chart.
To add milestones, drag the another measure based on days to the columns shelf (it can even be the same field). Right-click on the resulting pill in the columns shelf and choose "dual axis". Then right-click on the top axis in the chart and choose "synchronize axis". On the Marks shelf for this second measure, choose "Shape" (instead of bar), and select desired fields to be used color and shape.
If your data are more complicated than in the example (some events repeat, are not always in the same order, or each event does not immediately follow the next), then there is more control when working with a Gantt Bar (selected from the marks shelf, just as was done with Shapes). The measure that is placed on the columns shelf will indicate the day (number of days from day zero) on which an event starts, and the duration (in days) is determined by a measure placed on the size tile in the marks shelf. Don't stack the marks with this approach (from menu, Analysis, stack marks, off). Use the same approach as above for milestones (dual axis with shapes for marks).
Hopefully this gives you a place to start - good luck with your viz!