Skin dose map bugs

[dpla...@gmail.com]

Dear OpenREM users,

Two bugs have been discovered in the openSkin code that is used to calculate skin dose maps from fluoroscopy procedures. The bugs affect versions of OpenREM up to and including version 0.10.0:

Bug 1

For each x-ray field openSkin applies a combined backscatter factor and f-factor to convert air kerma to absorbed dose in water. The factor should account for kVp, copper filtration thickness and x-ray field size at the surface of the phantom. However, a bug means that the field size is not correctly accounted for, and the combined factor for a 5 x 5 cm field is always applied, regardless of the actual size of the field at the surface of the phantom. This bug has been fixed and the fix will be included in the next release of OpenREM. The bug is being tracked on Bitbucket as issue 935 (https://bitbucket.org/openrem/openrem/issues/935).

Bug 2

When an exposure has a non-zero caudo-cranial angle the size and shape of the field at the skin surface is incorrectly calculated. This bug will cause issues with the skin dose map because it affects whether fields overlap one another or not. The bug has not yet been fixed but will be before the next release of OpenREM. The bug is being tracked on Bitbucket as issue 933 (https://bitbucket.org/openrem/openrem/issues/933).

We recommend that openSkin maps are not used until these bugs are fixed.

Kind regards,

David Platten and Jon Cole