Halcyon APBI‐VMAT plans
PO‐MLC
HOT SPOTS
For benchmarking, all clinical APBI plans were re‐optimized in Eclipse TPS for Halcyon RDS via the same number of partial arcs, identical collimator rotations, and identical arc geometry (including the TrueBeam VMAT arc length). Additionally, the Halcyon couch structure was inserted, replacing the TrueBeam couch. To meet the Fast‐Forward trial's requirement, optimization objectives were similar, yet tighter to TrueBeam VMAT plans. Identical dose calculation algorithm, dose reporting mode, CGS and PO‐MLC optimizer were used for Halcyon APBI plans as mentioned above. For similar target coverage, Halcyon APBI plans were normalized identically to the corresponding clinical TrueBeam VMAT plans as described above, and the GTV global hot spots were limited to those of the respective TrueBeam APBI plans that were within 110% of the prescription dose.