Dosimetric performance of the new high‐definition multileaf collimator for intracranial stereotactic radiosurgery

The objective was to evaluate the performance of a high‐definition multileaf collimator (MLC) of 2.5 mm leaf width ([Formula: see text]) and compare to standard 5 mm leaf width MLC ([Formula: see text]) for the treatment of intracranial lesions using dynamic conformal arcs (DCA) technique with a dedicated radiosurgery linear accelerator. Simulated cases of spherical targets were created to study solely the effect of target volume size on the performance of the two MLC systems independent of target shape complexity. In addition, 43 patients previously treated for intracranial lesions in our institution were retrospectively planned using DCA technique with [Formula: see text] and [Formula: see text] systems. The gross tumor volume ranged from 0.07 to [Formula: see text] with an average volume of [Formula: see text]. All treatment parameters were kept the same for both MLC‐based plans. The plan evaluation was performed using figures of merits (FOM) for a rapid and objective assessment on the quality of the two treatment plans for [Formula: see text] and [Formula: see text]. The prescription isodose surface was selected as the greatest isodose surface covering [Formula: see text] of the target volume and delivering 95% of the prescription dose to 99% of target volume. A Conformity Index (CI) and conformity distance index (CDI) were used to quantifying the dose conformity to a target volume. To assess normal tissue sparing, a normal tissue difference (NTD) was defined as the difference between the volume of normal tissue receiving a certain dose utilizing [Formula: see text] and the volume receiving the same dose using [Formula: see text]. The CI and normal tissue sparing for the simulated spherical targets were better with the [Formula: see text] as compared to [Formula: see text]. For the clinical patients, the CI and CDI results indicated that the [Formula: see text] provides better treatment conformity than [Formula: see text] even at large target volumes. The CI's range was 1.15 to 2.44 with a median of 1.59 for [Formula: see text] compared to 1.60–2.85 with a median of 1.71 for [Formula: see text]. Improved normal tissue sparing was also observed for [Formula: see text] over [Formula: see text] , with the NTD always positive, indicating improvement, and ranging from 0.1 to 8.3 for normal tissue receiving 50% ([Formula: see text]), 70% ([Formula: see text]) and 90% ([Formula: see text]) of the prescription dose. The [Formula: see text] has a dosimetric advantage over the [Formula: see text] in Linac‐based radiosurgery using DCA method for intracranial lesions, both in treatment conformity and normal tissue sparing when target shape complexity increases. PACS number: 87.56J‐, 87.56 jk