This dosimetric study investigated the feasibility and effectiveness of a hybrid stereotactic radiosurgery technique combining dynamic conformal and volumetric modulated arcs for treating multiple small brain metastases in a single fraction, using two treatment planning systems: Elements and Monaco.

A clinical case involving multiple brain metastases was selected. Four treatment plans were generated: three using the Elements treatment planning system – (i) a volumetric modulated arc therapy plan (Cranial SRS); (ii) a dynamic conformal arc therapy plan (Multiple Brain Mets); and (iii) a hybrid dynamic conformal arc with volumetric modulated arc therapy plan – and a fourth using the Monaco treatment planning system with a volumetric modulated arc technique. Plans were assessed using quality indices, including target coverage, conformity, gradient and homogeneity indices, and doses to organs at risk. Quality assurance evaluation was performed with the stereotactic radiosurgery StereoPHAN™ phantom, MapCHECK® detector, and EBT-XD™ film. The gamma passing rates were analysed using 3 %/1 mm criteria. All plans were delivered using a 6 MV flattening filter-free photon beam on a Versa HD™ linear accelerator.

The hybrid planning technique demonstrated superior plan quality, with a significant reduction in the volumes of normal brain tissue receiving at least 10 Gy and 12 Gy, as well as lower doses to organs at risk, in accordance with established stereotactic radiosurgery guidelines. Quality assurance evaluation confirmed the dosimetric accuracy of the hybrid plan, showing excellent agreement between measured and calculated dose distributions, with a gamma passing rate exceeding 98 %.

For single-isocentre, multitarget stereotactic radiosurgery, the hybrid technique could represent a promising approach, offering improved sparing of surrounding normal tissues and consistent plan quality. However, these results need to be validated in larger clinical cases.