We have to reconsider the multiplicity of Technique in a Treatment Phase and not require the same Technique for all Plans summarized in a Phase. Consequently, treatments using a different technique must not enforce that the treatment is recorded as a separate Phase. Two reasons for this came up in discussions within our company and when trying to model some real examples: Plan revisions during the delivery of a Phase may change the Technique, e.g. from IMRT to VMAT, but are still considered as continuation of the same phase. In particular, fraction counting should not be forced to start over at 1 just because the technique was changed in a plan revision. In the extreme case of adaptive treatment with a new plan each day, it should be possible to pick daily from plans with a potentially different technique, but record the treatment as one phase with continuous fraction numbering.
The second reason is symmetry with prescription. Often the technique may not be defined yet when prescribing the treatment. So if technique would be important to structure the treatment into phases, this information may be missing when structuring the prescription into Phases. What was prescribed as one Phase should also be recorded as one phase even if Technique varies between fractions or more than one technique is used to provide certain doses to a certain set of target volumes.

Suggested Change: In Teleradiotherapy Treatment Phase, increase the multiplicity of the technique extension to allow for multiple techniques. Revisit the description around phases to align with that. Check with Brachy experts whether the same is needed for Brachy.