Dear fluka users
I would like first to sincerely thank you for the continuous support. most of the technical difficult i faced during my fluka simulation were resolved by carefully following your YouTube tutorials and reviewing the solutions that provided to other researchers. I truly appreciate your efforts in supporting the research community.
I would like to summarize clearly what I have done and the observations I obtained.
I imported the RTPLAN into FLUKA using Flair and performed the simulation without modifying the beam geometry extracted from the DICOM file.
However, I consistently observed a dose shift when comparing the calculated FLUKA dose distribution with the RTDOSE from the TPS. This shift appeared in all patient cases.
To verify whether the issue was case-dependent, I tested a completely different case from another center. The same dose shift was observed.
After investigating further, I modified the isocenter Z-coordinate manually. Once I adjusted the Z position, the FLUKA dose distribution aligned with the RTDOSE distribution.
Regarding the MLCs:
I developed a code to extract and reconstruct the MLC leaf positions from the RTPLAN and successfully implemented them in FLUKA. The dose distribution with MLCs was correctly shaped around the target.
However, when applying translation to the MLC geometry, I noticed that the translation value required to match the TPS dose was not equal to the isocenter Z value from the RTPLAN, which theoretically should be the correct reference.
I tested different Z ranges for the MLC positioning:
First: zmin/zmax = 65–70 cm
Second: zmin/zmax = 27–36 cm
In both cases, the dose mismatch persisted unless I manually adjusted the translation value.
At this point, I suspect that the discrepancy may be due to:
A mismatch between the MLC Z-coordinate in my geometry and the actual physical distance of the MLC from the photon source in the Elekta head model.
A possible difference between how FLUKA interprets geometry reference planes and how the RTPLAN defines the isocenter.
Or a systematic offset between the source position, isocenter definition, and MLC plane implementation.
To help clarify the issue, I will attach the full set of MLC coordinates I extracted.
Please note that while the leaf coordinates vary laterally (X direction), their Z distance from the head is constant in my implementation.
From your experience, do you think the primary cause of this mismatch is the incorrect Z-position of the MLC relative to the source?
Or could it be related to how the RTPLAN is interpreted in FLUKA (e.g., beam reference plane vs. isocenter plane)?
900.flair (8.6 KB)
9000.inp (18.9 KB)
Best regards