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Dosimetric Evaluation of the Galaxy Rotating Gamma System for SRS/SRT

H Liu1*, A Eldib1, L Chen1, B Wang2, S Li2, C Miyamoto2, C Ma1, (1) Fox Chase Cancer Center, Philadelphia, PA, (2) Temple University Hospital, Philadelphia, PA

Presentations

PO-GePV-T-415 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: The Galaxy® RTi system, a gamma stereotactic radiosurgery (SRS) system with real-time image guidance technology, has been developed for high-precision SRS or frameless, fractionated stereotactic radiotherapy (SRT). This work investigated the treatment plan quality of Galaxy by comparing both the machine setup parameters and plan dosimetry parameters with those of the Leksell Gamma Knife® Perfexion™ (GK), which is widely used in the clinic for SRS/SRT.

Methods: The GK system (Elekta AB, Sweden) uses 192 static cobalt-60 sources to deliver noncoplanar beams while the latest rotating Gamma system Galaxy (Akesis, Concord, CA) uses 30 cobalt-60 sources to deliver non-coplanar, non-overlapping arcs simultaneously. Ten brain cancer patients were unarchived from our clinical database, which were previously treated on GK in our institution. The lesion volume for these cases vary from 0.1 cm3 to 15.4 cm3. Galaxy plans were generated using the Prowess TPS (Prowess, Concord, CA) using the same dose constraints and optimization parameters. Plan quality metrics of Galaxy plans such as target coverage (%volume receiving the prescription dose), D99, conformity index (CI), cone size, shots number, beam on time, and DVH curve, were compared with those of GK plans.

Results: Superior treatment plans were generated for the Galaxy system that met our clinical acceptance criteria. For the 10 patients investigated, the mean CI and dose coverage for Galaxy was 1.77±0.22 and 99.24±0.33%, compared to 1.94±0.48 and 99.19±0.67% for GK, respectively. The beam-on time for Galaxy was 17.42±5.79 minutes compared to 21.34±7.35 minutes for GK (both assuming dose rates at the initial installation).

Conclusion: The Galaxy® RTi system can provide dose distributions with similar quality to that of GK with less beam-on time. The system also capable of real-time image guidance at treatment position to ensure accurate dose delivery for SRS/SRT.

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