RT Structure Set¶

The focus for this Radiotherapy Structure Set IOD is to address the requirements for transfer of patient structures and related data defined on CT scanners, virtual simulation workstations, treatment planning systems and similar devices. Earlier this IOD also permitted the inclusion of the Audio module (based on Curves) but that feature was retired.

The RT modules introduced for RT Structure Set (among other RT IODs) are the Structure Set Module, the ROI Contour module and the RT ROI Observations. The Structure Set and the ROI Contour model define some structures which may based on some images (e. g. CT or MR). How this works is described at the RT Dose object, which uses the same mechanism to select structures and assign them doses. Instead of those doses, the RT ROI Observation Module is included to define the identification and interpretation of the ROIs specified in Structure Set and ROI Contour modules.

The RT ROI Observation Module¶

This module defines how the ROIs defined with Structure Set and ROI Contour modules are to be interpreted. Each item ( =observation) of the RT ROI Observation Sequence provides information about one ROI. Within the item there are different fields to describe the observation, e. g. a unique (for all items of this sequence) Observation Number, an Observation Label, etc. and also two sequence, the RT ROI Identification Sequence and the Related RT ROI Observations Sequence. Both are used to describe the interpretation of the ROI, e. g. for the latter there are some defined term code values, e. g. (defined terms) different volumes according to IRCU50: PTV (Planning Target Volume), CTV (Clinical Target Volume) or GTV (Gross Tumor Volume); or brachy information: BRACHY_CHANNEL (brachytherapie channel), ...; or ORGAN (patient organ), ISOCENTER (treatment isocenter to be used for external beam therapy) and so on.

In the RT Related ROI Sequence there can be referenced further ROIs which are related to the current one, e. g. to provide the information, that the current ROI is CTV enclosed from a PTV which is referenced in the sequence.