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--- planning:userguide:tutorials:patient_geometry [2017/08/03 16:05] – [Working with Points] dpatenaude
+++ planning:userguide:tutorials:patient_geometry [2021/07/29 18:28] (current) – external edit 127.0.0.1
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 ====== Patient Geometry ======
+===== Patient / External Structure =====
+The Patient or External structure is one of key importance in Astroid. This structure is used to define the extents of the dose calculation process. This includes the extents of the dose grid, as well as useful area of the CT images for the purposes of Relative Stopping Power conversion. Planners should be aware that all area outside of the External contour is considered to have an RSP value of 0.001 (air). As a result please ensure that any devices that need to be considered in the calculation such as: patient immobilization or positioning devices or the couch are contoured as part the external contour if they will be present during treatment and may impact the delivery beams. Please note in the example below how the planner included the head holder, mask, and S-frame as part of the External contour so that all of these devices will be included in the dose calculations. The couch was safely excluded in this example because no "through couch" beams were going to be used in this treatment. This "air" override is applied **BEFORE** any manual user overrides are applied.
+ {{ :planning:userguide:tutorials:externalcontout.png?800 |}}
 ====== Structures ======
 Within Astroid the planner has the ability to create additional structures that may be needed when building a treatment plan. The Astroid Planning App allows for new structure creation using modifications of existing structures only. These modifications include boolean combinations, expansions/contractions, rinds, and clipping (i.e. splitting by a plane).
 ===== General Structure Options =====