Merged in bugfix/RAM-3901_elekta_symmetry_docs (pull request #437)

warning of elekta symmetry calculation issue.

Approved-by: Randy Taylor

docs/source/field_analysis.rst

@@ -478,6 +478,16 @@ Symmetry is calculated over the specified field width (e.g. 80%) as set in by ``
 Symmetry can be positive or negative. A negative value means the right side is higher.
 A positive value means the left side is higher.
 
+.. danger::
+
+    The official formula is above but due to a bug in pylinac, the actual result returned
+    is missing the 100 multiplication factor. For backwards compatibility, this is being
+    left as-is for now, but may change in a future version. Workarounds include:
+
+    * Multiplying the result by 100.
+    * Use the newer :ref:`field-profile-analysis` module which has the correct formula for
+      the :ref:`point difference quotient <point-difference-quotient>`.
+
 .. _siemens_protocol:
 
 Siemens

docs/source/topics/profiles.rst

@@ -317,6 +317,8 @@ Example usage:
 .. [#] `Gao et al Eqn 1 <https://aapm.onlinelibrary.wiley.com/doi/epdf/10.1002/acm2.12315>`__
 .. [#] Doselab and SNC call this the "CAX point difference" however Doselab does not multiply by 100. Yet, at least in the case of Doselab, the example assumes the values are ~100. In Pylinac, we often assume values are ~1. In such a scenario, the resulting value is the same.
 
+.. _point-difference-quotient:
+
 Symmetry (Point Difference Quotient)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^