Room: Track 6
Stereotactic radiosurgery (SRS) of large brain lesions (> 3 cm in size) remains challenging due to poor local control and increased risks of adverse radiation effects. In this study, we aim to develop an adaptive dose painting (ADP) approach to integrate spatial fractionation (such as volume-staged treatment) with temporal fractionation (such as hypofractionated treatment) to improve SRS of large brain lesions.
As initial benchmark study, an ADP algorithm was developed for a dedicated SRS system (Gamma Knife Icon) by placing and optimizing hundreds of isocenters inside a target. ADP varies the fractional dose distribution so that the dose to pre-divided sub-target volumes was sequentially boosted from one treatment fraction to another while the whole target volume receiving the same fractional dose. The algorithm was tested for 10 cases of large brain lesions (8.4±3.2 mL in volume). A generalized biological effective dose (gBED) was formulated to assess voxel-by-voxel dose variations across individual treatment fractions (3-5) for the whole treatment delivery. The resulting dose distribution metrics (gBED, conformity, dose gradient surrounding the target, etc.) were compared with the conventional treatment approach where no dose variation was applied for each treatment fraction.
For all the cases, ADP significantly increased the mean gBED to the target (p<0.04) while maintaining identical target volume coverage (range 97%-100%) and the dose conformity index (range 0.65 to 0.87) of the conventional treatment approach. Such an increase was more pronounced for the late-responding tissue than for the early-responding tissue (For example, 16.7% for a/ß =2 Gy versus 8.1% for a/ß= 10 Gy). The peripheral dose gradient index (GI) agreed within 2% among all fractional ADP treatments, and within 3.5% of the theoretical minimum for every case.
Simultaneous spatial and temporal hypofractionation is demonstrated for SRS of large brain lesions with a new ADP approach.