Once the Course has been completed the next block will be the Patient Model. The Patient Model contains a single CT image set and all contour variants (targets and organs at risk) associated with these images.

• Patient Model: captures the state (anatomy) of a patient at a certain point in time. Each Patient Models contains a single Image Set (typically CT) and all contour (structure) variants associated with these images. Each unique Image Set imported into the patient should produce a new Patient Model. Each unique structure set imported into the Patient Models should produce new contour variants for each unique contour. Each contour may have only a single “active” variant and the plan will automatically update based on the selection of the active variant.
• Variant: A specific model of a target, OAR, or other structure. A physician may provide an initial target contour and a treatment plan might be generated using this information. The physician may later (using the same CT image set) provide a revised target contour. Rather than import this revision as a new structure or override the original, you may specify this new contour as a variant of the original and the plan will automatically update based on the selection of this new active variant (note each contour/structure may have one or many variants, but only a single variant can be designated as “active”).

There are multiple levels that various structures can live at. Each level will effect how the structure will relate to the plan.

Site level structures are predefined templated structures. The user is not allowed to edit any aspect of a Site Level structure. Site level structures may be used for prescriptions as long as they have been designated as a Target.

Course level structures are not predefined templated structures (Site Level Structures). Course level structures may have certain properties edited within the planning user interface (e.g.: their type). A structure may be assigned as a Course level structure by choosing the box “New Course Structure” option at the time of import for any structure that does not automatically match a Site Level Structure. Structures that have been changed to Course level will have be designated as such by the word “course” appearing in parentheses beside the structure name during import. This is useful when a structure was misnamed during the contouring process. Course level structures that have been designated as Target structures can also be used for prescriptions. Any structure with TV as part of its name will automatically be designated as a Course Level structure.

Custom structures show up at the Patient Model level. These are structures that were not part of the templated structures nor assigned as a Course Level structure. The user has the option to edit the properties of a custom structure from within the Patient Model task.

Plan level structures are structures created with the Astroid TPS. These structures are derived from existing structures (e.g.: expansions, combinations). See Patient Geometry on how these are created.

The structures type determines the options available to the user when specifying constraints and objectives for the treatment plan optimization (refer to Optimization Constraints and Optimization Objectives for definitions of Constraints and Objectives). Below explains the structure types and options available for each type during optimization:

For structure types that are not Target or Other the user only has the ability to set constraints and objectives that drive the dose downward.

• Constraints: only maximum and maximum mean dose settings can be added to the structure.
• Objectives: only minimizing objectives (minimize the maximum, minimize the mean, and minimize the overdose) can be added to the structure.

For structure types that are Targets and Other the user has the ability to set constraints and objectives that drive the dose upward and downward.

• Constraints: Both maximum and minimum dose and mean dose constraints can be added to the structure.
• Objectives: Both minimizing and maximizing dose objectives cab be added to the structure.

Within Astroid the planner has the ability to view the Patient Model details and edit certain structures in a limited capacity.

1. A Patient Model contains data relating to the image set such as the number of slices, who imported the image set, the import date and the UID.
2. A Patient Model also contains a list of the structures that were imported.
3. The user may choose to set the active variant for any structure present in the snapshot.
4. Structures not defined in the site config (i.e. custom structures) are denoted with a “c” beside it. These structures have the ability to be edited in a limited capacity. The planner may choose to change the structure variant, color, and structure type. The planner may also choose to enter any notes that may be helpful at this point.