The aim of this work package is to provide the experimental data for small photon fields in the presence of magnetic fields, in order to inform the investigation of small field characteristics in MRgXT and to contribute to the data set of correction factors in WP1.

This experimental data needs measurement of the ratio of dosimeter readings between a small field and a reference field as a function of field size for photon beams in presence of magnetic fields. In addition, lateral profiles in small fields will be measured.

The coordinated and well-designed set of measurements performed in this work package carried out at five available facilities will demonstrate the agreement of small field characteristics in the presence of magnetic fields and to which extent the experimental facilities can be used as test facility for small field dosimetry in MRgXT.

Finally, techniques for remote dosimetry will be investigated and developed for small field measurements in MRgXT. This is necessary to validate the consistency of dose measurements between facilities and can potentially be used for (remote) dosimetry audit techniques in future.