This is the MapCheck2 (w/MapPhan) model we use here at North Star Lodge Cancer Center, for VMAT QA. This is a 351 slice CT, with a structure set containing 11 structures.

We are only overriding 3 structure densities. The Top_Plate = 600 HU, the Diode_Plane = -200 HU, and the Bottom_Plate = 0 HU.

*** This dataset should not be expected to work for you clinic without adjustment. ***

This is the testing procedure we used here at North Star Lodge Cancer Center to dial-in the HU values for the density overrides.
This procedure is intended for the MapCheck2 device with the MapPhan solid water build-up sleave.


Setup the MapPhan as normal, at the end of your couch. Set the scored-marks on the MapPhan so that the diode plane is at your linac's isocenter.

Obtain MapCheck2 meassurements for a 10x10 cm field in the AP direction, the PA direction, and shoot a 10x10 cm field as a full arc. Do this for each energy.

For each energy, make note of the relative readings between the AP, PA, and Arc (using the central diode value).


In Eclipse... setup the same fields as described above, and calc the QA plans. Compare the realative readings for AP, PA, and Arc in Eclipse to the relative readings as measured above. Also, ensure that the dose delivered to the central diode for the AP field in Eclipse matches your TPR(d=5,fs=10) value in your beam data... this ensures that your dose calibration will be correct.


Tweak the HUs as necessary to get the relative ratio of the fields in Eclipse to match the actual meassurements, while keeping the dose to the central diode of the AP field matching your beam data.