ESTRO 2025 - Abstract Book

S2725

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Results:

Figure 1 compares plan quality for the PTV and OARs, expressed as a percentage change (percentage change = (6FFF plan - 6X plan) / 6X plan). The 6FFF plans achieved similar ipsilateral lung sparing and improved contralateral lung sparing compared to the flattened beam plans. Notable volume reductions include Lung_R (5Gy) and Breast_R (4Gy), with median changes of -10.2% and -4.4%, respectively. Dose reductions were observed for the Heart (2cc) and Breast_R (0.04cc), with median changes of -3.3% and -4.5 %, respectively. The FFF plans also showed an average increase in monitor units (MU) of 22.7%. Gamma pass rates for RadCalc calculations and ArcCHECK measurements, using a 3%/2 mm criteria, were comparable, as shown in Table 1.

Conclusion: FFF plans provided lower or comparable dose coverage compared to flattened beam plans, with greater contralateral lung sparing observed for unflattened beams. The increase in MU for unflattened beams, due to their profile shape at larger field widths, can be offset by the higher dose rate offered by FFF beams, thereby maintaining or reducing delivery time [2] which would be advantageous for deep-inspiration breath hold treatments [3]. RadCalc and ArcCHECK results independently confirm that 6FFF beams can be clinically used in VMAT delivery for unilateral breast treatment.

Keywords: radiotherapy, breast cancer, FFF beam

References: [1] Xiao Y, Kry SF, Popple R, et al. Flattening filter ‐ free accelerators: a report from the AAPM Therapy Emerging Technology Assessment Work Group. Journal of Applied Clinical Medical Physics . 2015;16(3):12-29.