Spot-wise compensation of proton beam deflection and radiation field deformation in the transverse magnetic field of an in-beam MR scanner using a research version of a commercial treatment planning system
In brief
Proton spot correction restores dose plans with over 98.5% measurement agreement
In representative proton therapy cases, two spot-wise correction methods restored target coverage, dose uniformity, and organ sparing to levels seen in plans without a magnetic field. Dose measurements agreed with calculations at more than 98.5% of points under the study's 3%/3 mm test; patient-specific correction performed better, while clinical use remains to be tested.
- Journal
- Physics in medicine and biology (Q1)
- Published
- 22 October 2026
- Study design
- Unclassified
- Evidence level
- Level 5, Expert Opinion (CEBM 5)
- Authors
- Marisa Cobanaj, Erik Traneus, Felix Horst, Krishna Jeanne Godino Padre, Stefan Menkel, Petra Trnkova, et al.
- PMID
- 42913708
- DOI
- 10.1088/1361-6560/aeb84d
Why clinicians should know about it
- Picked for Medical Physics (top studies of the week, 25 October 2026): Experimental proton dose compensation validated in MR field
Abstract
Objective
Magnetic resonance-integrated proton therapy (MRiPT) offers the potential for high-precision, image-guided particle therapy but is challenged by magnetic field (MF)-induced proton beam deflection and radiation field deformation. Unless compensated for, these effects compromise dose conformity and prohibit clinical implementation. This work aims to develop and experimentally validate a spot-wise compensation method capable of restoring proton dose distributions in the presence of a measured 3D magnetic vector field map within a clinical treatment planning system (TPS).
Approach
A spot-wise compensation framework was implemented in a research version of RayStation, a TPS commercially available for clinical use. The method compensates both lateral beam deflection and MF-induced radiation field deformation by shifting individual pencil-beam spots based on displacement vectors derived from dose calculations in water phantoms using the measured MF of an in-beam MR scanner integrated with a horizontal proton beamline. Two complementary strategies were implemented: a patient-specific approach based on plan-specific displacement calculations, and a generic approach using precomputed displacement maps derived from a reference phantom. Compensation performance was evaluated in representative clinical cases. Dose distributions were experimentally validated using 2D ionisation chamber array measurements.
Main Results
Both compensation methods effectively restored target coverage, dose homogeneity, and organ-at-risk sparing to the level of no-MF reference plans. The patient-specific method generally achieved a higher performance, whereas the generic compensation method enabled rapid automated correction with sufficient accuracy for clinical workflows involving deep-seated tumours. Local γ-analysis demonstrated excellent agreement between measured and calculated doses, with pass rates exceeding 98.5% for 3%/3 mm criteria.
Significance
This work demonstrates that compensation of MF-induced proton beam deflection and field deformation can be achieved entirely within a research version of the RayStation TPS using measured, MR scanner-specific MF data. The proposed method provides a scalable, robust framework for future MRiPT clinical applications.
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Abstract as published, via PubMed.
For healthcare professionals. The summary is generated by AI from the published abstract, and the evidence level is assigned automatically from the study design on the Oxford CEBM hierarchy. Neither is medical advice. Read the full paper before changing practice.