Planning study comparing TrueBeam and TrueBeamSTx 10MV FFF VMAT beams for single fraction treatment of brain metastases

International Conference on Medical Physics

August 03-05, 2015 Birmingham, UK

Isabelle Gagne and Isabelle Vallieres

Posters-Accepted Abstracts: J Nucl Med Radiat Ther

Abstract :

With its high-resolution MLC and flattening-filter free mode, the emerging Varian TrueBeamSTx platform has recently been shown to improve the efficiency of stereotactic radiosurgery of brain metastases without significantly compromising target coverage, conformity and homogeneity. Given that our center is equipped with 5 TrueBeams with Millenium MLC and only 1 TrueBeamSTx with high-resolution MLC, we investigated the differences in plan quality between the high-resolution and Millenium MLC for single fraction treatment of brain metastases using 10MV FFF beams. Ten CT datasets were randomly selected from previously treated patients with brain metastases. For every patient, 2 VMAT 10MV FFF plans were generated, one using the TrueBeam with Millenium MLC and the other one using the TrueBeamSTx with high-resolution MLC. A third VMAT-plan was created using the standard 6MV beam on the TrueBeamSTx for baseline comparison. Plan quality was assessed by analysis of conformity, homogeneity & dose gradients (50%, 25% & 10%). As previously reported, no significant differences in plan quality was observed between the TrueBeamSTx 10MV FFF and standard 6MV VMAT plans. Statistically significant differences in homogeneity (1.15 vs. 1.17) and the 50% and 25% dose gradients (50%: 6.62cc vs. 7.92cc; 25%: 40.38cc vs. 46.74cc) were observed between the high-resolution and Millenium MLC 10MV FFF plans. However, all 10MV FFF plans (high-resolution & Millenium) met the clinical objectives without major deviations enabling the time-sensitive single fraction treatment of brain metastases to be potentially delivered on either TrueBeam linear accelerator.