Minor: in some places Isppa is incorrectly used

[KTZ228]

Most people familiar with the literature would notice this issue.
For newcomers, however, using Isppa where Ipa or a different variable should be used can be confusing.

An explanation can be found in: https://doi.org/10.1016/j.clinph.2021.12.010

[jkosciessa]

@KTZ228 Can you indicate specific instances where you would replace Isppa?

[KTZ228]

So long as the intensity readout does not refer to a single value. So whenever we're talking about a grid containing intensity values, for example, it should be Ipa. Isppa would be used to describe the maximum value in skull or skin for example.