Low QA passing rate when using ArcCheck and blocked structures

Good afternoon,

we recently discovered some issues when using arccheck to verify plans in our Radixact with blocked structures (such as the arms in craniospinal irradiation, for example). All the low dose regions are overestimated by 3%.

We did some testings by blocking 90º and opossed sectors in the arccheck and other plans in phantoms before contacting Sun Nuclear support. However, they have not provided us with any information or solution. I have also asked them detailed info about how the RTPlan correction is done, since not applying the RTPlan correction improves slightly the results.

We wanted to ask if anyone had experienced this issues. Thank you for your time!