ESTRO 2023 - Abstract Book

S1581

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ESTRO 2023

Fig 1: Impact of collimator material on the 2D pMBRT dose profile.

Results The smallest throughput reduces the valley dose and produces the lowest VPDR. The latter can be additionally lowered by decreasing CPD. This however is limited by the adverse effect of secondary radiation. The highest neutron yield is observed from the tungsten collimator but it outperformed most other commonly used materials of the same thickness considering the dose profile (fig. 2). The nuclear activation and secondary neutron production of the tungsten collimator can be reduced, however, using a pre-collimator of suitable materials and dimensions. For a similar treatment plan, which is suitable for e.g. brain tumours, a tungsten thickness between 25 mm to 30 mm is found sufficient for the implemented energy range. We find ctc = 2 mm with ~50 % throughput is an optimum configuration to preserve the uniformity of dose at the evaluated PTV which will be used for future biological characterization at DCPT.