Author: Hyunuk Jung, Fiona Li, Brian Marples, Michael Milano, Sean M. Tanny, Dandan Zheng, Yuwei Zhou 👨🔬
Affiliation: Department of Radiation Oncology, University of Rochester, University of Rochester Medical Center, University of Rochester 🌍
Purpose:
Recurrent GBM remains one of the most challenging cancers, with limited treatment options. We investigated potential planning parameters of SFRT, a novel radiotherapy technique that delivers dose heterogeneously (with high-dose sub-volumes) throughout the target. We aimed to optimize SFRT delivery, with the hope of improving outcomes for patients with recurrent GBM.
Methods:
To determine feasible SFRT planning parameters, we identified five patients with recurrent GBM who had received conventionally fractionated reirradiation. We replanned an single-fraction SFRT course for these patients. SFRT vertices were generated in the PTV using a published script, exploring a range of parameters for vertex radii and spacing, along with a manual vertex design to target ~10% of. A peak dose of 15Gy was prescribed to the vertices, while the valley dose was constrained below 5Gy. Optimal vertices size and spacing, manual adjustment strategy, and preliminary dosimetric analyses was evaluated
Results:
Preliminary findings demonstrated that effective SFRT plans can be achieved with vertex radii of 4-7.5 mm and center-to-center spacing of 30-40 mm. For automated vertex generation, the optimal parameters included a 4 mm radius and 21-25 mm spacing. Adjustments were made to increase vertex radii to 4-7.5 mm within the GTV until the total vertex volume reached ~10% of the GTV. The preliminary physical-dose composite plan replacing one fraction of the conventional plan with SFRT demonstrated no significant differences in OAR dose, while peak-to-valley ratios consistently exceeded 3 for SFRT.
Conclusion:
This study proposed feasible SFRT planning parameters and demonstrated the potential to combine SFRT and conventional radiotherapy to deliver tumoricidal doses partially to the GTV while sparing normal tissue and OARs. We present optimal vertex size and spacing parameters for future studies of SFRT in the context of recurrent GBM treatment.