Halcyon MLC preset


I am setting up some QA tests for Halcyon using pylinac, specifically the picket fence tests. Halcyon has 2 MLC banks- distal and proximal. Each bank consists of 1cm width leaves, with a 0.5cm offset between the two banks giving effectively 0.5cm leaf width at isocentre.

The pylinac MLC class has presets for each of these MLC banks, each consisting of 60 leaves with 0.5cm width, with an 0.25 cm offset between the centers of proximal and distal.

Am I missing something here? Does this not mean there is an effective leaf width of 0.25cm? Should the widths in each bank not be 1cm?



I’m finding a better alignment with the leaf centers for each MLC by using the following MLCArrangements


mlc_config = pylinac.picketfence.MLCArrangement(leaf_arrangement=[(28, 10)])


mlc_config = pylinac.picketfence.MLCArrangement(leaf_arrangement=[(29, 10)],offset = 0.5)

These seem to match the description of the Halcyon MLC given in this reference: https://aapm.onlinelibrary.wiley.com/doi/pdf/10.1002/acm2.12568

Using my custom MLCArrangement to analyse proximal MLC

Compared to using the HALCYON_PROXIMAL preset:


I’ll read the paper and adjust as needed. When I created the MLC config the halcyon was brand-spanking new and the details were unclear. Sounds like I may have jumped the gun.

Would you mind sending me images of distal and proximal PFs? Looks like you’re right, I just want to verify. Thanks! https://forms.gle/rgSmhgWw2A34AmH58

Hi James, Apologies I thought I had already replied. Please find attached.

Hi Dominic, I’m implementing this and your donated images are great but appear to have the labels swapped? The one labeled “distal” matches the image you’ve posted above. Other than that everything looks good and matches up and the fix should be in the next release.