Winston-Lutz module

Hello all,
I’m happy to say that I’ve made some good headway on a new Winston-Lutz module for pylinac. 2D comparison of BB-to-field center is fairly easy. I’m currently working on an algorithm to calculate isocenter size, not from the BB, but using the BB as a reference point. In this way, the BB doesn’t have to be centered–in fact it can be anywhere in the radiation field. These two references are my basis: Du et al, Winkler et al.

If you have any W-L images that you’d like to donate to the test suite you can upload them here. If you have a TB with MPC, sending those results in too would be appreciated.

Also, if you have dynalogs/trajectory logs for picket fence deliveries (along with the image), those would be appreciated as well.

Let me know if you have any suggestions or questions,


Dear James,

I sent to you images for W_L test with tow ball size …
thank you

Good afternoon James. How are you?

My name is Rafaela, i’m a Medical Physicist in São Paulo-Brazil.

I’ve got one doubt:

The coordinate system represented in Pylinac uses as reference the treatment room or the image to be analysed?

Thank you so much!

Hello Rafaela,
welcome. The coordinate space is absolute to the treatment room.

Dear James,

About the couch isocenter for me there is something not clear…

  • "Determine couch isocenter size - Instead of using the BB as the non-moving reference point, which is now moving with the couch, the Reference image (gantry = collimator = couch = 0) CAX location is the reference. The movement of the BB relative to the Reference image CAX will form a semicircle (assuming the BB cannot be placed exactly at isocenter). The optimization is run to minimize the distance of each point to the edge of a circle. The optimum radius will determine the isocenter size."

The optimum radius should help us to define the center of the circle, I mean the isocenter position but not the isocenter couch size… because the circle radius depending of the BB position, more the BB is far form the couch isocenter more the radius of the circle increase ==> iso size increase too…and it should not

For me the iso size for the couch could be the difference between the gantry isocenter position (find in the first step analysis ) and isocenter couch position (ie. the center of the circle). And the entire linac isocenter could be the mean position of the 3 isocenter positions col, gantry, and couch…
Are you agree ?