Hello,

I guess I’m a trouble maker.

So I’m doing Winston Lutz on a Halcyon for SRT…

(working with what we have at the moment… please no comments from the peanut gallery)

The field edge defined center seemed to be off a bit from EPID - so my chief asked to get values of BB to EPID based center instead of BB to CAX as defined by field edge.

Thought there would be a quick flag to choose from but there wasn’t.

Is anyone else interested in this? My chief’s justification was he wanted to just test IGRT and placement of BB in MV fields in his Winston Lutz and not also add the complexity of the field edge from the MLCs.

Example 1.13 mm reduced to 0.69 mm.

My quick cheater’s way to calculate this

was to replace the definition of CAXtoBB with EPIDtoBB. This probably will screw with some calculations but I will also probably reduce all the other info outputs to only show max/median EPID to BB distance and the graphs (with EPID to BB shown):

def cax2bb_vector(self) → Vector:

“”“The vector in mm from the CAX to the BB. #JSH “””

dist = (self.bb - self.epid) / self.dpmm

return Vector(dist.x, dist.y, dist.z)def cax2bb_distance(self) → float:

“”“The scalar distance in mm from the CAX to the BB. #JSH “””

dist = self.epid.distance_to(self.bb)

return dist / self.dpmmversus Original:

def cax2bb_vector(self) → Vector:

“”“The vector in mm from the CAX to the BB.”“”

dist = (self.bb - self.field_cax) / self.dpmm

return Vector(dist.x, dist.y, dist.z)def cax2bb_distance(self) → float:

“”“The scalar distance in mm from the CAX to the BB.”“”

dist = self.field_cax.distance_to(self.bb)

return dist / self.dpmm