Según lo que he leído "manualized" en este contexto siginifica que el tratamiento en si, está estandarizado, es decir, sigue un patrón de pasos previamente definidos en un manual del tratamiento del problema en cuestión.
Acá te dejo una versión en inglés:
Manualized treatments are treatments that have exact steps, so that each person has relatively the same treatment.

Usually, they have inclusion criteria (adults with generalized anxiety disorder), and exclusion criteria (cannot be in another treatment for anxiety). When studies are completed on a manual, you know their results should be found on most people who meet the criteria for the study.

Having a manual ensures that the results will be similar, no matter the therapist. It also allows for one specific form of therapy to be tested.

For example, to empirically test "cognitive behavioural therapy" does no good, because there are so many varieties of cognitive behavioural therapy. How long were the sessions? What did they do? How many weeks did it last? A manual includes all that, so it can be replicated.

Some manuals simply say the bare details, while others are completely (or nearly completely) scripted.

Los ejemplos de abajo son el mismo, traducidos para que te des una idea. Espero haber sido de ayuda, ¡saludos!